Dissertations / Theses on the topic 'TiAlN coating'

This project has as main goal to study the influence of the coating thickness, deposited by arc-PVD- technology, on the wear resistance of coated cemented carbide inserts in three different turning operations. An additional effort has also been made to develop a new test method for evaluating flank wear resistance. Three different coating types (Coating A, Coating B and Coating C) have been studied in three distinctive thicknesses (2, 4 and 6 μ m) for each type. For two of the coating types (Coating A and B) special studies has been done with the thickest coating, creating two additional coating versions of the thickest coating, by changing various deposition parameters, with the aim to enhance the cohesive properties of the coating and lower the residual stresses at the cutting edge. The results show increased crater wear resistance with increased coating thickness for all coating types, but the amount of increase changes with coating type (Coating A>B>C). Flaking wear resistance decreased with increased coating thickness for all coating types. Further the high temperature version of Coating A, showed a significant increase in the flaking wear resistance compared to the standard version of Coating A. The flank wear test showed an increased resistance with thicker coatings in all cases except for the 6 μ m version of Coating C. The flank wear resistance of the most flank wear resistant coatings (Coating B, C) was also successfully examined in a new developed test method. The method suppressed excessive crater wear on the rake face and presented a high abrasive wear rate on the flank and some flaking on the rake face. The amount of flaking is judged not to influence the testing of the flank wear resistance. For all the tested coatings in the new test an increase in the coating thickness resulted in better flank wear resistance.

Hard nanostructured TiAlN coatings have gained high importance in the field of protective tribological coatings. Nevertheless, their use regarding high temperature (>800°C) applications such as dry high speed machining still remains a challenge. Addition of elements such as Ta or Y has shown a beneficial impact on these properties. But for a better performance of these coatings, an in-depth understanding of their oxidation and wear mechanisms over a wider range of temperatures is needed which is currently unavailable in the literature. This work investigated the wear and oxidation properties of AlTiTaN hard coatings deposited by reactive magnetron sputtering at a substrate temperature of 250°C. Depending on process conditions, coatings with a preferential crystallographic orientation of cubic {111} or {200} with a columnar microstructure were observed. The oxidation and wear mechanisms for these coatings were investigated between 700°C and 950°C in air for various test durations. Further, the influence of Y doping in AlTiTaN coating was also studied.By combining Dynamic-Secondary Ion Mass Spectrometry ,X-ray diffraction (XRD) and Transmission Electron Microscopy measurements, it was demonstrated that a single amorphous oxide layer comprising of Ti, Al and Ta oxides formed at 700°C became a bilayer composed of a crystalline Al rich layer (protective Al2O3) and a Ti/Ta rich oxide layer at 900°C. The oxidation mechanism was governed primarily by inward diffusion of O at 700°C while from 800°C onwards outward diffusion of Al and inward diffusion of O controlled the reaction rate. A correlation between the oxidation kinetics and wear mechanism of AlTiTaN coatings, investigated at 700°, 800° and 900°C, was established.
Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished

In recent years, TiAl intermetallic alloys been widely used in aircraft and automotive industry. With the aim of improving the mechanical behavior and the oxidation resistance at high temperature of the TiAl alloys firstly designed, new intermetallic alloys of second and third generation have been successively developed. In this work, the oxidation resistance in air of four intermetallic alloys of second generation (Ti-48Al-2Cr-2Nb) and third generation ( Ti-48Al-2Nb-0.7Cr-0.3Si, Ti43.5Al-4Nb-1Mo and Ti-47Al-2Cr-8Nb) was investigated by TGA equipment under isothermal conditions in the range of 800-1000 °C. These alloys were cut from the core of bars, previously processed by Electron Beam Melting and successively heat-treated. The composition of the oxide layers was investigated by XRD, SEM-EDS and XPS. Each alloy showed different oxidation behavior at high temperatures. Layer exfoliation or spallation was observed for many samples, but at very different temperatures for the different alloys. When spallation did not happen in a significant extent the oxide layers grew according to a parabolic law. The kinetic rate constants and the activation energies were calculated. These kinetic parameters allowed to assess a rank of oxidation resistance, which can be correlated with the composition of the alloys. In order to improve the oxidation resistance of Ti-48Al-2Cr-2Nb, ceramic nitride coatings were deposited by a High Power Impulse Magnetron Sputtering (HiPIMS) method. Differently engineered TiAlN and TaAlN protective films were processed and their performances compared. Samples were submitted to thermal cycling under oxidizing atmosphere up to 850° C (40 cycles) and 950°C (100 and 200 cycles), at high heating and cooling rates. For this purpose, a burner rig able to simulate the operating conditions of the different stages of turbine engines was used. The microstructure and composition of samples before and after oxidation were investigated by several techniques: microscopy (optical and SEM-EDS), X-ray photoelectron spectrometry (XPS) and X-ray diffraction (XRD). All the TiAlN coatings differently processed provided a remarkable improvement of oxidation resistance. Good adhesion properties were observed even after repeated thermal shocks. HiPIMS pretreatments of the substrate surfaces, performed before the coating deposition, significantly affected the oxidation rate, the oxide layer composition and the coating/substrate adhesion. The oxide layers formed on the sample surface showed different thickness, depending on the presence of the protective coating and the processing path adopted for its deposition. The nitride coatings appreciably enhanced the oxidation resistance and sustained repeated thermal shocks without showing damage or spallation. Differently TaAlN coating did not improve the oxidation resistance of TiAl substrate.

The oxidation behaviour of TiAlN based hard coatings with the addition of Cr and/or Y was investigated using scanning electron microscopy, scanning/transmission electron microscopy, energy dispersive X-ray analysis, thermogravimetry and X-ray diffraction. The coatings were deposited using the combined cathodic arc/unbalanced magnetron deposition technique. The main practical application of these films is dry high speed cutting in difficult to cut materials such as AISI A2 steel. Especially in the case of TiAlCrYN coating with an oxynitride and Cr-enriched overcoat, extensive research on the oxidation behaviour was performed and described here. Heat treatments in air between 600-1000°C for different duration were carried out. The Ti[0.44]Al[0.54]Cr[0.02]N coating was used as the starting point for the investigations. The effect of heat on the composition of the interface region was investigated. This region is of utmost importance for the adhesion of the film. In the case of TiAICrN the interface stability was not guaranteed because of diffusion of the substrate elements Cr and Fe to the coating surface after annealing for 1h at 900°C. In comparison, the diffusion of substrate elements Cr and Fe in a ~2.3 mum thick coating of Ti[0.43]Al[0.52]Cr[0.03]Y[0.02]N and of Ti[0.34]Al[0.62]Cr[0.03]Y[0.01]N with overcoat, reached only a distance of ~600nm into the coating. This was achieved by the diffusion of Y to the grain boundaries. Y probably reacted at the same time with inward diffusing O. The diffusion of Y to the boundaries was observed after heat treatment for 1h at 900°C or 10h at 800°C.Ti[0.26]Al[0.26]N/Cr[0.48]N was the coating with the least oxide layer growth after oxidation for 1h at 900°C. An oxide layer thickness of only ~100nm was measured. For the TiAICrYN coating with overcoat an oxide layer of 230nm and for TiAICrYN of 430nm formed after 1h at 900°C. TiAlCrN in comparison formed an oxide layer of ~800nm after 1 h at 900°C.The oxide layers formed after 1h at 900°C consisted mainly of an Al[2]O[3] and TiO[2] bi-layer in the case of TiAlCrN and TiAlCrYN. The addition of a Cr-rich oxynitride overcoat led to the formation of a mixture out of Al[2]O[3], Cr[2]O[3] and TiO[2] in the oxide layer. In the case of TiAlN/CrN, a solid solution consisting of Cr[2]O[3] and Al[2]O[3] was observed. In general a stress relief after heat treatment was observed. At the same time the formation of voids along the column boundaries was identified. This was explained with the relaxation and diffusion of defects created during the deposition process. The effect of different substrate materials on the oxidation behaviour was also investigated. It was found that the formation of substrate oxides on the coating surface is very much dependent on the onset point of oxidation of the substrate material itself. The oxidation of substrate material occurred mainly through growth defects and pinholes. In cases where cracks formed during heat treatment of the coating, the formation of oxides out of substrate elements were observed in cracks connecting the substrate with the coating surface. Changing the bias voltage altered the formation of cracks. This research emphasises the importance of Y in the oxidation mechanism of TiAlN based hard coatings. Y blocks the diffusion path along the column boundaries and thus stowed down the diffusion and oxidation process. At the same time the addition of Cr can increase the oxidation resistance considerably, which was observed in the TiAlCrYN coating with and without overcoat.

TiAlN and TiAlN-based coatings that are used of relevance as protection of cutting tool inserts used in metal machining have been studied. All coatings were deposited by reactive cathodic arc evaporation using industrial scale deposition systems. The metal content of the coatings was varied by using different combinations of compound cathodes. The as-deposited coatings were temperature annealed at ambient pressure and in some cases also at high pressure. The resulting microstructure was first evaluated through a combination of x-ray diffraction and transmission electron microscopy. In addition, mechanical properties such as hardness by nanoindentation were also reported. TiAlN coatings with two different compositions were deposited on polycrystalline boron nitride substrates and then high pressure high temperature treated in a BELT press at constant 5.35 GPa and at 1050 and 1300 °C for different times. For high pressure high temperature treated TiAlN it has been shown that the decomposition is slower at higher pressure compared to ambeint pressure and that no chemical interaction takes place between TiAlN and polycrystalline cubic boron nitride during the experiments. It is concluded that this film has the potential to protect a polycrystalline cubic boron nitride substrate during metal machining due to a high chemical integrity. TiZrAlN coatings with different predicted driving forces for spinodal decomposition were furthermore annealed at different temperatures. For this material system it has been shown that for Zr-poor compositions the tendency for phase separation between ZrN and AlN is strong at elevated temperatures and that after spinodal decomposition stable TiZrN is formed.

TiAlN/VN multilayers, with a layer periodicity of ~3nm, have exhibited superior sliding wear resistance (1.26xlO-17m3N-lm-l) and lower friction coefficient (~=0.4, pin-on-disc test, Ah03 ball counterpart) when compared to other commonly used wear protective coatings, e.g. TiN, TiAlN and TiAlN/CrN. They require excellent oxidation and wear resistance for dry high speed machining operations. This project investigates the microstructure of the as-deposited coatings, their oxidation degradation mechanism and their wear and friction properties at room and elevated temperatures. The microstructure of the starting films was studied in terms of intermixing between the TiAlN and VN individual layers caused by the absence of shutters during the industrial PVD deposition. A FEGTEM coupled with EELS revealed chemical distribution of individual layers at nanometre resolution. Cs corrected STEM allowed the composition of individual atomic columns to be imaged. It was also used to probe across the interface of TiAlN/VN with angstrom beam (1 A) using EELS which showed a 1±0.1 nm thick intermixing between TiAlN and VN. Film growth and elemental distributions were therefore theoretically predicted in association with substrate rotation. The experimental compositional profiles and the prediction showed good agreement. The coatings deposited with -75 V and -85 V substrate bias voltage were multilayer TiAlNNN, 37at%:::;V:::;55at%, 0.81:::;(Ti+Al)/V:::;1.73, which were used for subsequent oxidation and wear studies. The oxidation behaviour of these coatings in air was investigated using thermal gravimetric analysis up to 1000°C and compared to TiN and TiAlN. Static oxidation of TiAlN/VN films was studied in the range 550-700°C, and characterised by high temperature in-situ X-ray diffraction and STEM/EDXlEELS of selected surface cross-sections. The oxidation resistance of TiAlN/VN was found to be controlled by the VN layers and consequently oxidation was initiated at a lower temperature than TiN and TiAlN coatings. The onset for rapid oxidation of the TiAlN/VN coating was found to be 2550°C. At temperatures >600°C, a duplex oxide structure was formed; the inner layer comprised a porous region of Ti-rich and V-rich nanocrystallites, while several phases were observed in the outer region, including V20 5, Ti02 and AlV04. V20 5 was the dominant oxide at the outer layer at 2638°C. An Au marker study suggested roughly equal diffusivity of cations outward and oxygen inward diffusion occurred during oxidation. Further to the oxidation study, dry sliding ball-on-disc wear tests of TiAlN/VN (V 55.2at%, Ti 28.5at% and Al 16.3at%) coatings on flat stainless steel substrates were undertaken against Ah03 at 25°C, 300°C and 635°C in air to investigate the relation between the presence of V 205 and low friction. The friction coefficient was 0.53 at 25°C which increased to 1.03 at 300°C and decreased to 0.46 at 635°C. Detailed investigation of the worn surfaces was undertaken using site-specific TEM via FIB, along with FTIR and Raman spectroscopy. Microstructure and tribo-induced chemical reactions at these temperatures were correlated with the coating's wear and friction behaviour. The friction behaviour at room temperature is attributed to the presence of a thin hydrated tribofilm and the presence of V 205 at high temperature.

A typical hard coating on metal cutting inserts used in for example turning, milling or drilling operations is TiAlN. At elevated temperatures, TiAlN exhibits a well characterized spinodal decomposition into coherent cubic TiN and AlN rich domains, which is followed by a transformation from cubic to hexagonal AlN. Using in-situ synchrotron x-ray radiation, the kinetics of the second transformation was investigated in this thesis and the strong temperature dependence on the transformation rate indicated a diffusion based nucleation and growth mechanism. The results gave additional information regarding activation energy of the transformation and the critical wavelength of the cubic domains at the onset of hexagonal AlN. After nucleation and growth, the hexagonal domains showed a striking resemblance with the preexisting cubic AlN microstructure. During metal cutting, the tool protecting coating is subjected to temperatures of ~900 ºC and pressure levels in the GPa range. The results in this thesis have shown a twofold effect of the pressure on the decomposition steps. Firstly, the spinodal decomposition was promoted by the applied pressure during metal cutting which was shown by comparisons with annealed samples at similar temperatures. Secondly, the detrimental transformation from cubic to hexagonal AlN was shown to be suppressed at elevated hydrostatic pressures. A theoretical pressure/temperature phase diagram, validated with experimental results, also showed suppression of hexagonal AlN by an increased temperature at elevated pressures. The spinodal decomposition during annealing and metal cutting was in this work also shown to be strongly affected by the elastic anisotropy of TiAlN, where the phase separation was aligned along the elastically softer <100> directions in the crystal. The presence of the anisotropic microstructure enhanced the mechanical properties compared to the isotropic case, mainly due to a shorter distance between the c-AlN and c-TiN domains in the anisotropic case. Further improvement of the metal cutting behavior was realized by depositing individual layers with an alternating bias. The individual bias layers exhibited microstructural differences with different residual stress states. The results of the metal cutting tests showed an enhanced wear resistance in terms of both crater and flank wear compared to coatings deposited with a fixed bias.

Gamma TiAl based alloys are considered as alternative materials to Ni based superalloys for applications in gas turbine engines. However, they exhibit low oxidation resistance above 700 °C. The need to develop oxidation resistant coatings for gamma-TiAl based alloys was the motivation for this project. Three TiAlCr-X coatings were studied: These were the Ti-50Al-10Cr (TiAlCr) and Ti-48Al-9Cr-4B (TiAlCrB) coatings and the Ti-48Al-9Cr-4B with Ag interlayers multilayer (TiAlCrB/Ag) coating. The coatings were deposited on Ti-48Al-2Nb-2Mn alloy and Si wafer substrates by RF sputtering using optimised deposition parameters. A pure Ag and two alloy (Ti-50Al-10Cr and Ti-48Al-9Cr-4B) targets were used for sputtering. The coatings were studied by SEM, EPMA, XRD, XPS, TEM, DSC, DTA and TG. The morphology and the microstructure of the as-deposited coatings on Si and Ti- 48Al-2Nb-2Mn substrates were the same. All the coatings exhibited dense columnar morphology with ~1 mum thick columns for the TiAlCr and TiAlCrB and coarser columns for the TiAlCrB/Ag. The TiAlCr and TiAlCrB coatings were amorphous with randomly dispersed alpha-Ti nanocrystals. In the TiAlCrB the nanocrystals were smaller (< 15nm) and their volume fraction slightly higher than in the TiAlCr. Thermodynamic calculations confirmed that alpha-Ti is the second favourable phase to form after the amorphous phase at the Tdeposition used. For 1 mum/h deposition rate the amorphous phase formation in the as-deposited microstructure was possible for Tdeposition up to 208 and 223 °C for TiAlCr and TiAlCrB respectively. This variation in Tdeposition is attributed to the higher melting point of the Ti-48Al-9Cr-4B alloy (1123 °C compared to 1080 °C for TiAlCr), which affects the mean surface diffusion length, hi the TiAlCrB/Ag coating the microstructure consisted of crystalline Ag and amorphous TiAlCrB layers. The thermal stability of the as-deposited coatings was assessed by thermal analysis of freestanding deposits and the phase evolution path from the as-deposited metastable to the equilibrium microstructure for TiAlCr and TiAlCrB was defined by XRD and TEM. The TiAlCr crystallized at 657, 690 and 714 °C when heated at 5, 20 and 50 K/min heating rates, respectively. The activation energy for crystallization was 293 KJ/mol, which is very close to the activation energy for volume diffusion of Ti in the gamma phase. The amorphous phase transformed first to the gamma-TiAl and alpha2-Ti3Al phases and then the equilibrium Ti(Cr,Al)2 Laves phase formed very slowly at the expense of the alpha2. The TiAlCrB crystallized at 685, 686 and 690 °C when heated at 50, 65 and 80 K/min heating rates, respectively, with activation energy for crystallization 613 KJ/mol, which indicates the enhanced stability of the TiAlCrB. The phase evolution path of the TiAlCrB was the same with TiAlCr, with the addition of fine borides from the early stages of crystallization. The microstructure of the TiAlCrB was finer than TiAlCr after crystallization. Formation of alpha-Ti nanocrystals ( > 50nm), was noticed when the amorphous TiAlCr was heated at 550 °C, but not in the TiAlCrB after heating at 600 °C, which confirmed the enhanced stability of the TiAlCrB. The oxidation of the coatings, the substrate and target alloys was assessed by TG at 800 °C for 200 hours. The weight change per unit area and the parabolic rate constants were determined for each material. Mixed alumina and titania scales were formed on the specimens. Clusters of coarse titania crystals tended to form on the surface of the scales. Their formation was favoured by the surface roughness of the specimens. The TiAlCrB exhibited the best oxidation resistance of the three coatings, followed by the TiAlCrB/Ag and the TiAlCr.

Quaternary cubic (TixCr1 − xAl~ 0.60)1 N1 coatings with 0 < x < 0.33 have been grown using reactive cathodic arc evaporation. When adding Ti the hardness was retained after annealing up to 1100 °C which is a dramatic improvement compared to CrAlN coatings. The coatings showed an age hardening process caused by spinodal decomposition into coherent TiCr- and Al-rich cubic TiCrAlN domains and the formation of hexagonal AlN precipitates and cubic TiCrN domains in the vicinity of the grain boundaries. The improved hardness was attributed to the stabilization of the cubic structure suppressing the formation and growth of hexagonal AlN. Furthermore, the presence of Ti atoms generated incoherent nanometer-sized crystallites within the hexagonal AlN precipitates disrupting the hexagonal lattice during the coarsening process. The addition of Ti promoted the formation of a TiO2 layer over Al2O3 resulting in a lower oxidation resistance. However, by tuning the composition it is possible to design coatings to have both good oxidation resistance and good high temperature mechanical stability.

Funding Agencies|SSF project Designed multicomponent coatings, MultiFilms||

This work aimed to study the effect of surface oxidation of TiAl intermetallic alloys, its fracture behavior and study the formation and stability of picked coatings that could prevent these phenomena. ?-TiAl alloy (Ti46Al7Nb) was examined by three different coatings (AlCr, AlCrN and AlCrNAg). Firstly, it was carried out short-term exposure to high temperature in an inert atmosphere for all coatings. Secondly, there were experiments of cyclic exposure to high temperature in normal atmosphere and isothermal high-temperature exposure in a normal atmosphere. During high-temperature experiments in normal atmosphere mass gain was measured and it was monitored a surface texture. Finally, the most promising coatings were chosen, and those were evaluated in bending strength.

Nanoscale TiAlCN/VCN multilayer coating was deposited in an industrial size 1000x4 Hauzer Techno Coating machine capable to operate with both unbalanced magnetron sputtering (UBMS) and high power impulse magnetron sputtering (HIPIMS) mode. The work was directed to study the impact of HIPIMS on the microstructure of the nanoscale TiAlCN/VCN coating, in relation to its properties at both room and elevated temperatures. TiAlCN/VCN coatings were deposited by three different ways in combination of reactive UBM and HIPIMS technique. These are (i) reactive pure UBMS, (ii) reactive combined UBMS and HIPIMS, (iii) reactive pure HIPIMS. The microstructure and mechanical properties of the nanoscale TiAlCN/VCN coatings deposited in all the above combination of deposition have been studied. In all three cases, coatings were deposited in three major steps: (a) HIPIMS etching by Ar[+] + V[+] ions (b) a 300 nm thick TiAIN base layer deposition in Ar + N[2] atmosphere followed by 2.5 pm thick TiAlCN/VCN coating deposition in mixed Ar+N[2]+CH[4] reactive atmosphere. PVD chamber furnished with two pairs of opposing magnetrons with TiAl and V targets were utilised deposit this coating. During the second case of combined deposition, two opposing magnetrons were enabled to operate in HIPIMS mode and other two magnetrons were operated in UBMS mode, where as in third case only two opposing targets with HIPIMS power supply were utilised to deposit the TiAlCN/VCN coating respectively. In all the three cases, deposition parameters such as bias voltage (U[b] = -75V), deposition temperature (T[s]= 450 °C) and total pressure of reactive gas mixture (Ar+N[2]+CH[4]; P = 4 X 10[-3] mbar) were maintained at similar conditions. The V+ HIPIMS etching used in all three processes has shown excellent adhesion (Lc > 50) of the coating to the substrate. The plasma compositional analysis of V+ HIPIMS etching has shown high metal-to-gas ion ratio with ionization states of V up to 5+. The ionic composition of the HIPIMS plasma as a function of discharge current was analysed by plasma sampling using energy-resolved mass spectrometery. During the coating of TiAlCN/VCN, the plasma analysis has confirmed the higher production rate of metal ions and free carbon in case of HIPIMS-UBM in contrast to pure UBM. This has resulted to a denser closed columnar microstructure of the coating during the HDPIMS-UBM technique than UBM. The formation of graded like microstructure achieved during reactive pure HIPIMS case, further plants the importance of HIPIMS in producing advanced nanostructured coatings for high technology applications.

Magnetron sputter deposition with single target materials was used to produce amorphous and crystalline Ti-A1-(Cr) alloy coatings on a Ti-50Al substrate. The following coatings were studied: Ti-50Al-10Cr, Ti-53Al-15Cr, Ti-50Al-20Cr and Ti-48Al. The microstructures of the coatings were studied in the as deposited condition and after devitrification and heat treatment. A random distribution of nano-precipitates was formed in amorphous as-deposited coatings. Columnar features were present when the as-received deposit had crystallised during sputter deposition. If crystallization occurred during deposition, a columnar microstructure formed with the columnar fibres being parallel to the deposition direction. For the Ti-50Al-10Cr and Ti-53Al-15Cr deposits, the crystalline domains consisted of lamellar gamma // alpha, i.e. the crystalline deposits had a gamma // alpha texture. The alpha → alpha transformation occurred during deposition. Phase competition in the alloys was studied by combining thermodynamic modelling and transformation kinetics. At 1173K, the Ti-50Al-10Cr alloy transformed to a two-phase microstructure, consisting of the gamma and C14 Ti(Al, Cr)2 phases. The Ti-53Al-15Cr alloy transformed to a three-phase microstructure, consisting of the gamma, tau and the C14 Laves phase. The gamma and tau phases were mixed finely, with gamma // tau. The Ti-50Al-20Cr alloy transformed to a two-phase microstructure, consisting of the gamma and the Cl4 Laves phase. No orientation relationship between the gamma and the C14 Laves phase was observed. Phase evolution studies at lower temperatures in the range 773K to 973K indicated that for the amorphous Ti-48Al alloy, the phase transformation path is: the amorphous phase → alpha → gamma + alpha/alpha2. A fine lamellar structure was formed, with gamma being the dominant phase. For the Ti-50Al-20Cr alloy, the phase transformation path was: the amorphous phase → gamma → gamma + Ti(Al, Cr)2. The experimental observations and the modelling results have clearly suggested a tendency of amorphous phase stabilisation via Cr addition. Thermodynamic modelling also indicated that the driving force for amorphous alloy formation is not much less than that for the precipitation of disordered solution phases. Kinetically, the amorphous phase formation during sputter deposition is related to the suppression of surface diffusion at low substrate temperatures. The temperature processing window for ordered phase formation in the Ti-Al(-Cr) alloys during magnetron sputter deposition was evaluated by the effective diffusion distance. Time dependent nucleation calculations showed that in the Ti-48Al amorphous alloy, it would be kinetically easier to precipitate the alpha phase than the gamma phase. In the case of the Ti-50Al-20Cr alloy, the gamma phase forms in preference of alpha, which is consistent with experimental observations. Diffusion phenomena at the coating/substrate interface and the oxidisation of the coatings were also studied. The experimental Cr diffusion profiles and the simulations for the Ti-Al-Cr coatings and the Ti-50Al substrate indicated that diffusion at 1173K is reasonably slow. The Ti-50Al-10Cr, Ti-53Al-15Cr and the Ti-50Al-20Cr coatings could form protective oxide scales at 1173K. When a columnar structure was present in the crystalline deposit, cracking of the coating was observed when the coating was subject to thermal cycling from elevated temperatures. It is concluded that if cracking of the coatings was to be avoided, amorphous deposits should be preferred.

Etwa 27000 Flugzeuge durchqueren täglich den Luftraum über Europa. Dieser weiter steigende Flugverkehr erfordert neue Richtlinien für die Luftfahrzeuge. Im Besonderen stehen CO2- und NOX-Emission, Kerosinverbrauch und Lärmbelastung unter Optimierungsbedarf. Diese Anforderungen wurden bis 2050 vom Advisory Council for Aerospace Research in Europe (kurz: ACARE) festgelegt und werden wissenschaftlich unterstützt [3, 4]. Um diese Ziele zu erreichen, gibt es verschiedene Forschungsprogramme, Clean Sky ist ein EU-Technologieprogramm davon. In diesem Projekt werden sechs Demonstrator-Programme entwickelt, von denen MTU Aero Engines eines gestaltet. Im Rahmen dieses Projektes wurde eine Weiterentwicklung des Getriebefan (Geared Turbofan-GTF) erreicht, bei dem Fan und Niederdruckturbine durch ein Getriebe voneinander entkoppelt sind. Durch die optimierte Drehzahl beider Komponenten (vergrößerter Fan - langsamer, Niederdruckturbine (LPT) - schneller) wird die Turbinenleistung gesteigert und gleichzeitig die Geräuschemission minimiert. Entwickelt wurde der GTF von Pratt & Whitney in Kooperation mit MTU Aero Engines. Herkömmliche Varianten sehen vor, dass die Niederdruckturbine u.a. den Fan antreibt und zwar nur so schnell, dass der äußere Radius des Fans die zulässige Geschwindigkeit nicht überschreitet. Die herkömmlich verwendeten Nickelbasislegierungen in der Niederdruckturbine haben mit 8 g/cm3 eine zu hohe Dichte um einige Anforderungen im ACARE wirtschaftlich erfüllen zu können. Bereits 1967 hat die US Airforce das große Potential zur Gewichtsreduzierung durch Titanaluminid-Legierungen (TiAl-Legierungen) mit einer Dichte von rund 4 g/cm3 im Hochtemperaturbereich der Flugzeugtriebwerke erkannt. Zwischen 1980 und 1990 entwickelte das General Electric-Forschungscenter die gamma-TiAl-Legierung Ti-48Al-2Cr-2Nb, welche als erste kommerzielle Titanaluminidlegierung in der Niederdruckturbine von Flugzeugtriebwerken eingesetzt wurde. Eine weitere Legierung dieser Werkstoffgruppe kam erst ca. 15 Jahre später zum Einsatz, die TNM-Legierung. Wie man an diesem Beispiel sehen kann, dauert die Integration neuer Werkstoffe in der Luftfahrt aufgrund der notwendigen Vorversuche und Sicherheitsaspekte teilweise 20 Jahre. Seit September 2014 kommt im Triebwerk PW1100G GTF von Pratt & Whitney die geschmiedete Version der TNM-Legierung zum Einsatz. MTU Aero Engines AG München baut hierfür die Niederdruckturbine. Durch die hervorragenden Hochtemperatureigenschaften der gamma-TiAl-Legierungen wie z.B. thermische Stabilität der Mikrostruktur, Resistenz gegen Titanfeuer und hohe spezifische Fes-tigkeit, konnten sich die Titanaluminide in Konkurrenz zu den Nickelbasislegierungen sehr gut platzieren. Deswegen werden die beiden gamma-TiAl-Legierungen (Ti-48Al-2Cr-2Nb, TNMTM) bereits in den letzten Stufen der Niederdruckturbine eingesetzt. Ein Nachteil der gamma-Titanaluminide ist die begrenzte Oxidationsbeständigkeit über 750 °C, wodurch das Einsatzfeld als Hochtemperaturwerkstoff stark begrenzt wird. Um das Anwen-dungspotential der gamma-Titanaluminide weiter zu steigern und auch bei Temperaturen über 750 °C einzusetzen, ist eine Steigerung der Oxidationsbeständigkeit notwendig. Die Oxidationsbeständigkeit kann durch das Aufbringen von Oxidationsschutzschichten wie z.B. Al2O3 erreicht werden. Welche neben der Korrosionsbeständigkeit auch die thermisch-mechanischen Anforderungen des Substrat-Schicht-Verbundes sicherstellen müssen. Zur Erhöhung der Temperaturbelastbarkeit von gamma-TiAl-Schaufeln können zur thermischen Isolation keramische Wärmedämmschichten (WDS) aufgebracht werden. Aufgrund der WDS können höhere Prozesstemperaturen realisiert und die Lebensdauer des Grundwerkstoffs verlängert werden. Die Lebensdauer der Wärmedämmschichten und das Betriebsverhalten werden unter anderem durch eine gute Haftung auf dem Untergrund, eine niedrige Wärmeleitfähigkeit und einen thermisch stabilen Phasenaufbau bestimmt. Die Kombination aus Oxidationsschutz und Wärmedämmung wird bereits für Nickelbasislegierungen in der Brennkammer und Hochdruckturbine der Flugzeugtriebwerke eingesetzt. Um gamma-Titanaluminide in weitere Stufen der Niederdruckturbine oder Hochdruckturbine einzubringen, müssen diese Temperaturen von mindestens 900 °C aushalten und erfordern ebenso Beschichtungen zum Oxidations- und Wärmeschutz. Diese Schutzschichten finden für gamma-Titanaluminide bisher jedoch noch keine Anwendung.

Cette étude met en évidence le rôle des lacunes d’azote et des défauts structuraux dans l’ingénierie de revêtements durs à stabilité de phase améliorée et dont les propriétés mécaniques sont compatibles avec des applications à haute température. Le nitrure de titane et d’aluminium (Ti,Al)N sous forme de revêtements est un matériau de choix pour la protection des outils de coupe pour métaux en raison de sa résistance supérieure à l’oxydation et à l’usure à haute température. La décomposition spinodale à haute température de la phase métastable cubique (Ti,Al)N en domaines cohérents de taille nanométrique de c-TiN et de c-AlN donne une dureté importante aux températures élevées. Un apport thermique encore plus élevé conduit à la transformation de c-AlN en w-AlN, ce qui nuit aux propriétés mécaniques du revêtement. Un moyen de retarder cette transformation est d'introduire des lacunes d'azote. Dans cette thèse, je montre que la combinaison d’une réduction de la teneur globale en azote du revêtement c-(Ti,Al)Ny(y <1) avec une faible tension de polarisation du substrat lors du dépôt par arc cathodique induit un retard encore plus prononcé de la transformation de la phase c-AlN en w-AlN. Dans de telles conditions, le durcissement par vieillissement est conservé jusqu'à 1100 ° C, ce qui correspond à la température la plus élevée signalée pour les films de (Ti,Al)N. Au cours des opérations de coupe, le mécanisme d'usure des films c-(Ti0.52Al0.48)Ny déposés par arc cathodique avec des teneurs en N de y = 0.92, 0.87 et 0.75 est influencé par l'interaction des lacunes d'azote, de la microstructure et des réactions chimiques avec le matériau de la pièce. Le revêtement y = 0.75 contient le plus grand nombre de macroparticules et présente, après usinage, une microstructure non homogène qui en abaisse la résistance à l'usure sur les flancs et les cratères. Le durcissement par vieillissement de l'échantillon y = 0.92 entraîne une résistance supérieure à l'usure sur le flanc, tandis que la structure dense de l'échantillon y = 0.87 empêche l'usure chimique qui se traduit par une excellente résistance à l'usure sur les cratères. Des films hétéroépitaxiés c-(Ti1-x, Alx)Ny (y = 0.92, 0.79 et 0.67) ont été déposés sur des substrats de MgO(001) et (111) en utilisant une technique de pulvérisation magnétron pour examiner en détail les défauts structuraux pendant la décomposition spinodale. À 900 °C, les films se décomposent pour former des domaines cohérents riches en c-AlN et c-TiN de forme allongée le long de la direction <001>. Les cartographies de déformation montrent que la plupart des contraintes se trouvent près de l'interface des domaines ségrégés et à l'intérieur des domaines c-TiN. Les dislocations s'agrègent favorablement dans c-TiN plutôt que dans c-AlN car ce dernier a une directionnalité plus forte des liaisons chimiques covalentes. À température élevée, la taille de domaine des films de c- (Ti, Al)Ny orientés (001) et (111) augmente avec la teneur en azote. Cela indique qu'il y a un retard dans le grossissement dû à la présence de plus de lacunes d’azote dans le film. [...]
This study highlights the role of nitrogen vacancies and defect structures in engineering hard coatings with enhanced phase stability and mechanical properties for high temperature applications. Titanium aluminum nitride (Ti,Al)N based materials in the form of thin coatings has remained as an outstanding choice for protection of metal cutting tools due to its superior oxidation resistance and high-temperature wear resistance. High-temperature spinodal decomposition of metastable (Ti,Al)N into coherent c-TiN and c-AlN nm-sized domains results in high hardness at elevated temperatures. Even higher thermal input leads to transformation of c-AlN to w-AlN, which is detrimental to the mechanical properties of the coating. One mean to delay this transformation is to introduce nitrogen vacancies. In this thesis, I show that by combining a reduction of the overall N-content of the c-(Ti,Al)Ny (y < 1) coating with a low substrate bias voltage during cathodic arc deposition an even more pronounced delay of the c-AlN to w-AlN phase transformation is achieved. Under such condition, age hardening is retained until 1100 °C, which is the highest temperature reported for (Ti,Al)N films. During cutting operations, the wear mechanism of the cathodic-arc-deposited c-(Ti0.52Al0.48)Ny with N-contents of y = 0.92, 0.87, and 0.75 films are influenced by the interplay of nitrogen vacancies, microstructure, and chemical reactions with the workpiece material. The y = 0.75 coating contains the highest number of macroparticles and has an inhomogeneous microstructure after machining, which lower its flank and crater wear resistance. Age hardening of the y = 0.92 sample causes its superior flank wear resistance while the dense structure of the y = 0.87 sample prevents chemical wear that results in excellent crater wear resistance. Heteroepitaxial c-(Ti1-x,Alx)Ny (y = 0.92, 0.79, and0.67) films were grown on MgO(001) and (111) substrates using magnetron putter deposition to examine the details of their defect structures during spinodal decomposition. At 900 °C, the films decompose to form coherent c-AlN- and c-TiN- rich domains with elongated shape along the elastically soft <001> direction. Deformation maps show that most strains occur near the interface of the segregated domains and inside the c-TiN domains. Dislocations favorably aggregate in c-TiN rather than c-AlN because the later has stronger directionality of covalent chemical bonds. At elevated temperature, the domain size of (001) and (111)- oriented c-(Ti,Al)Ny films increases with the nitrogen content. This indicates that there is a delay in coarsening due to the presence of more N vacancies in the film. The structural and functional properties (Ti1-x,Alx)Ny are also influenced by its Al content (x). TiN and (Ti1-x,Alx)Ny (y = 1, x = 0.63 and x = 0.77) thin films were grown on MgO(111) substrates using magnetron sputtering technique. Both TiN and Ti0.27Al0.63N films are single crystals with cubic structure. (Ti0.23,Al0.77)N film has epitaxial cubic structure only in the first few atomic layers then it transitions to an epitaxial wurtzite layer, with an orientation relationship of c-(Ti0.23,Al0.77)N(111)[1-10]ǀǀw-(Ti0.23,Al0.77)N(0001)[11-20]. The w-(Ti0.23,Al0.77)N shows phase separation of coherent nm-sized domains with varying chemical composition during growth. After annealing at high temperature, the domains in w-(Ti0.23,Al0.77)N have coarsened. The domains in w-(Ti0.23,Al0.77)N are smaller compared to the domains in c-(Ti0.27,Al0.63)N film that has undergone spinodal decomposition. The results that emerged from this thesis are of great importance in the cutting tool industry and also in the microelectronics industry, because the layers examined have properties that are well suited for diffusion barriers

Au cours de ce travail, des revêtements intermétalliques TiAlx (x=1,2,3) ont été élaborés sur des substrats à base titane : le titane pur et l'alliage commercial, TA6V. L'objectif était de réaliser des revêtements d'aluminiure en surface et d'étudier le comportement des matériaux revêtus vis-à-vis de l'oxydation à haute température sous air, sous air enrichi en vapeur d'eau et en présence de soufre. Les matériaux revêtus ont été testés à trois températures : 700°C, 800°C et 900°C. Les revêtements ont été réalisés à 1000°C par la méthode de cémentation en caisse. Les revêtements réalisés par ce procédé sont toujours adhérents au substrat. Pendant la réaction d'oxydation, l'existence d'un processus de rétrodiffusion de l'aluminium modifie la nature des phases et l'organisation du revêtement. Les phases TiAl et TiAl2 ne sont pas suffisamment riches en aluminium pour promouvoir la formation d'une couche d'alumine protectrice quelle que soit la température d'oxydation. Lorsque ce sont ces phases qui sont à la surface du revêtement, on assiste toujours à la formation d'une couche superficielle de rutile TiO2. Quand elle constitue la sous-couche externe du revêtement, la phase TiAl3 est assez riche en aluminium pour former une couche d'alumine -Al2O3 couvrante, compacte et protectrice.

Proučavane su koroziona postojanost i tendencija lepljenja različitihmaterijala u kontaktu sa tečnom Al–Si–Cu legurom. Ispitivanjem suobuhvaćeni čelik za rad na toplo, plazma nitrirani čelik i dupleksslojevi sa CrN, TiAlN, TiAlSiN i CrAlN prevlakama, različitog nivoapovršinske hrapavosti. Za ispitivanja pomenutih fenomenaprimenjena je metoda izvlačenja, koja je unapređena kako bi se povećalenjena tačnost i verodostojnost simulacije procesa livenja. Korozioniefekti su pojačani tako što su uzorci osim kratkog kontakta sa odlivkomzadržavani i u dužim periodima u kontaktu sa tečnom legurom (5 i 20min). Uprkos opštim stavovima, za ispitivane materijale jeustanovljeno da su sile izvlačenja uzoraka iz Al–Si–Cu odlivakanezavisne od njihovog hemijskog sastava. Uticaj hrapavosti je izraženkod uzoraka sa prevlakama kod kojih pri smanjenju hrapavosti dolazi dopovećanja sile izvlačenja. Sve ispitane prevlake su sklone mehaničkomlepljenju Al–Si–Cu legure za svoje površine, ali sa aspekta korozije utečnom metalu značajno prevazilaze performanse čelika i plazmanitriranog sloja. Duži kontakt livene legure sa površinama prevlakauzrokovao je niže vrednosti sila izvlačenja, što je posledicaoksidacije površina prevlaka. Ustanovljeno je da su ispitivaneprevlake inertne ka tečnoj leguri aluminijuma. Međutim, dolazi dooksidacije i korozije materijala podloge kroz greške rasta koje suprisutne u prevlakama. Stečena znanja o identifikovanimmehanizmima habanja i propadanja zaštitnih slojeva prevlakaposlužiće daljem razvoju dupleks slojeva namenjenih za zaštitu alataza livenje pod pritiskom.
Corrosion resistance and soldering tendency of different materials in moltenAl–Si–Cu alloy were studied. Hot-working tool steel, plasma nitrided steel andduplex layers with CrN, TiAlN, TiAlSiN and CrAlN top coatings, which wereproduced to various degree of surface roughness, were covered by the study.An ejection test was employed for investigation of the concerned phenomena.The ejection test was improved in order to increase its accuracy and thereliability of process simulation. Samples were examined in both short andextended periods of contact (5 and 20 min) with liquid casting. Castingsolidification was extended in order to intensify the corrosion effects. Contraryto common findings, it was found that the ejection force of the investigatedmaterials does not depend on their chemical composition. For the coatedsamples, a pronounced dependence of the ejection force on the surfaceroughness was found. The ejection force increases with decrease in surfaceroughness. All investigated coatings are prone to mechanical soldering by Al–Si–Cu alloy. Still, their corrosion resistance substantially exceeds the corrosionresistance of steel and plasma nitrided layer. Longer exposure of coatedsamples to cast alloy induced lower ejection forces, which is a consequenceof coatings oxidation. It was found that the investigated coatings are inert toliquid aluminium. However, the underlying material undergoes oxidation andcorrosion through coating growth defects. The findings concerning the wearmechanisms of protective layers support further development of duplex layersintended for die casting tools protection.

碩士
國立彰化師範大學
電機工程學系
102
Abstract The growth of machine tool manufacturing industry in recent years brings the improvement of precise machine processing technology and the increasing demand of cutting tools. Since the cutting tools are consumption material, it becomes an urgent problem to be solve to extend the lifetime and wear out problem of cutting tool. In this study, the characteristic of TiAlN tool coating is applied on the cutting tool with the metal feature of wearlessness and heat resistant in TiAlN, which optimizes the cutting tool life time and saves the production cost on machinery manufacturing. Through the data of experiment and scanning electron microscope (SEM) to observe the condition of coating components and compare the variance for further understanding of cutting tool life time. The experiment on indentation hardness is mainly operated on coating to analyze the wearlessness hardness of different coating materials. The difference to two cutting tools is therefore identified according to the material experiments and statics data compression by SPC control chart. The result shows that cutting tools with TiAIN coating reduces the wearness of cutting tools. Also, the hardness is increased and the tolerance is reduced to less than 56% during processing, this considerably increases the lifetime of cutting tools. Moreover, 47 % of the manufacturing cost is saved with the practical value for industry. Keywords: TiAlN Coating、Tungsten Carbide Cutting Tool、SPC、Average Variance。

碩士
明道大學
材料暨系統工程研究所
95
In this work, nano-multilayer TiSiN/TiAlN films have been deposited on WC-Co substrates by using TiSi (80:20 at.%) and TiAl (50:50 at.%) alloy target on a dual cathodic arc plasma evaporation system. The influences of bias voltages, holder speed rotation and reaction gas pressure varied on the microstructure, adhesion strength and tribological properties of the films were investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD) techniques were employed to analysis the microstructure, grain size, residual stress and bi-layer thickness. Corrosion test were used by Potentiostat to analysis the corrosion potential. Vicker’s hadrness and tribometer tester were used to measure the mechanical and tribological properties of nano-multilayer TiSiN/TiAlN thin films. The results showed that the hardness of the films ranged from 24-27 GPa, which the value is lower than both of TiAlN (29 GPa) and TiSiN (35 GPa). The coefficient of steady-state friction of the films against Cr steel ball ranged from 0.45 to 0.6, and TiSiN and TiAlN is 0.6 and 0.7, respectively. It has been found that the microstructure, adhesion strength and wear properties of the films were dependent on bias voltage, interlayer design bi-layer thickness and grain size in film structure, resulting from both improved adhesion strength and wear properties of nano-multilayer TiSiN/TiAlN coatings.

碩士
大同大學
材料工程學系(所)
93
Austempered ductile iron (ADI) possesses high tensile strength, wear resistance, fatigue resistance and low cost, and it is widely applied on mechanical parts. In general, austempering temperature of ADI is in the range of Ms~450℃, thus, the traditional heat treatment at high temperature for case hardening is not available to treat ADI. This research used the method of cathodic arc plasma deposition (CAPD) to coat TiN/TiAlN on ADI substrate and explored the effect of the surface coatings on corrosion behaviors of ADI. Moreover, XRD, HRc and SEM were further utilized to analysis the various properties of the coating films. The results showed that the hardness of the coated ADI is higher than that of uncoated ADI. However, the surface of coated ADI specimens is rougher than that of uncoated ADI. The adhesion between film and ADI substrate is better than that between film and graphite substrate. After polarization curves test, it was found that the corrosion current of coated specimen is smaller than that of uncoated specimen. Moreover, in 10 Vol.％HCl and 10Vol.%H2SO4 solution , the coated specimens process the lower corrosion rate than uncoated specimen. Thus, it implied that ADI coated with TiN/TiAlN films can evidently raise the corrosion resistance in sea water,hydrochloric acid and sulphuric acid.

With the amalgamation of hard coating in cutting tools industries for three decades now, a stage with proven performance has been reached. Today, nearly 40% of all cutting tools used in machining applications are sheltered with coatings. Coatings have proven to dramatically improve wear resistance, increase tool life and enable use at higher speed. Over the years TiN, TiAlN and TiC have emerged as potential materials to coat machining tools. Chemical vapor deposition was the first technology to be used to deposit these coatings followed by physical vapor deposition. Currently, extensive use is being made of cathodic arc evaporation and sputtering for coatings components. The principal limiting factor in the performance of these cutting tools lies in their failure due to the brittleness of these coatings. These hard coatings, usually coated on soft steel substrates, are subjected to contact damage during service. This contact damage is driven by mismatch strain between the elastically deforming film on a plastically deforming substrate. Understanding of the contact damage is the key parameter for improvement in the coating design. Contact damage involves initiation of cracks and subsequent propagation within coating. Multiple cracking modes are seen in nitride coatings on soft substrate and mutual interaction of cracks may lead to spallation of the coating, exposing the substrate to extreme service conditions. Hence visualization of subsurface crack trajectories facilitates the classification of benign and catastrophic modes of failure, which consequently allows us to tailor the coating architecture to eliminate catastrophic failure. Multilayers have shown to perform better then monolayer coatings. In multilayer coatings, application specific particular properties can be engineered by alternately stack-ing suitable layers. The multilayer utilizes benefits of interfaces by crack deflection, crack blunting and desirable transition in residual stress across the interface. Hence, designing interfaces is the key parameter in the multilayer coating. However, very few studies exist that describe experimental visualization of deformation modes in multilayer coatings with different types of interfaces, e.g. nitride/nitride and nitride/metal. Thus the prime objective of the present study is to comprehend the influence of different interface structures as well as its architecture on the various contact damage modes in these coatings. TiAlN/TiN has shown better tribological properties compared to its constituent monolayers. There is an order of magnitude augmentation in loads for cracking without any hardness enhancement relative to monolayers of constituents, with the additional feature that both constituents exhibit similar hardness and modulus. The resistance to cracking is seen to increase with increase in number of interfaces. Hence this uniqueness in toughening without drastic reduction in mechanical properties provides the motivation for understanding the fundamental mechanisms of toughening provided by the interfaces in these hard/hard coatings. Another combination for the present study is with interfaces between hard-soft phases ZrN/Zr, a composite that seeks to compromise hardness in order to achieve greater toughness. The selected combination has potential of providing a model system without any substoichiometric nitrides influencing the interfacial structure. There is a great need to optimize the metal fraction/thickness for exploiting the benefits of toughening without much compromise on hardness and stiffness, since the principal applications of these coatings lies in preventing erosive and corrosive wear. As all the deformation modes in theses coatings are stress driven, the influence of different variables on stress field would dictate the emerging damage. To understand the role of stress fields on contact damage, finite element method and an analytical model was used to predict the stress field within the coating. The TiAlN/TiN coatings were deposited by cathodic arc evaporation, while sputtering was employed to procure the ZrN/Zr multilayer coatings with much finer layer spacing. Microstructural characterization of the as received coatings was done by XRD, scanning electron microscopy, focused ion beam cross section machining and transmission electron microscopy. Mechanical properties like hardness and modulus were evaluated by nanoindentation with restricted penetration depths to allow measurements that were not influenced by the substrate. Contact damage was induced by micro indentation at high loads. Indentations were examined from plan view as well as cross section for getting details of crack nucleation as well as propagation trajectories. Focused ion beam was used to examine cross sections of indents as well as to prepare electron transparent thin foils for transmission electron microscopy examination of subsurface damage induced by indentation. To emphasize specific issues in detail, the present work is divided into four sections: 1 Microstructure and mechanical characterization of the as deposited coatings of ZrN/Zr multilayer (while that of TiAlN/TiN has been reported elsewhere) 2 Details of contact damage in ZrN/Zr coating 3 Resolution of micro mechanistic issues in TiAlN/TiN coating utilizing detailed microscopy 4 The effect of change in architecture through heat-treatment of ZrN/Zr multilayer coatings on the mechanical behavior and contact damage Detailed microstructural, compositional and mechanical characterization was done on ZrN/Zr as received multilayer coatings. Thickness of metal layer was seen to influence the texture in the nitride, thick metal acquiring basal texture in turn inducing (111) texture in the nitride to reduce interfacial energy. Microstructure revealed that the nitride grows with interrupted columnar grains, renucleating at each metal/nitride interface. Presence of both phases was confirmed at even very low bilayer spacing, with slight changes in multilayers architecture, from planar interfaces to curved interfaces. The chosen system proved to be an ideal system for multilayer study without formation of secondary nitrides. Residual stress and hardness reduced with increase in metal layer thickness, whereas modulus was seen to follow the rule of mixture value. Detailed contact damage study of ZrN/Zr is reported in section two with influence of volume fraction and metal layer thickness. All the experimental results were corroborated with finite element methods. A comparative study of contact damage of multilayer with monolayer was carried out with cross section as well as plan view of indents. Metal plasticity was able to distribute damage laterally as well as vertically, hence reducing the stress concentration. There lies an optimum thickness of the metal providing maximum toughening by increasing the threshold load required for edge cracking. The sliding of columns is resisted by the metal. However, thick metal layers promote microcracking in individual nitride layers. Cracking is restricted to within individual nitride layers, eliminating through thickness cracking. The intermediate metal thickness was able to provide a mechanism of laterally distributing sliding and hence a higher tolerance level of the indentation strain that can be accommodated without cracking. Thin metal multilayers were seen to show delamination, strongly influenced by the multilayer architecture. We use the finite element method to understand the influence of stress fields in driving these various modes of damage for varying volume fraction and metal layer thicknesses. It is demonstrated how metal plasticity results in stress enhancement in the nitride layer compared to a monolayer and reduces the shear stress, which is the driving force for columnar sliding. The micro cracking to columnar shearing transition with metal thickness was explained with the help of average shear and normal stress across the multilayer which could explain the transition from cracking and sliding to interfacial delamination in thin metal layer multilayers with enhancement in interfacial shear stress. TiAlN/TiN multilayer allowed to exploit a form of compositional contrast to measure the strain with respect to depth. Layers acting as strain markers quantify the amount of sliding in terms of the offset in layers with respect to depth within the coating. We illustrate with transmission electron micrographs, the flaw generation that occurs as a result of sliding of misaligned column boundaries. These boundary kinks,upon further loading, may lead to cracks running at an angle to the indentation axis in an otherwise dense, defect free, as deposited coating. A previous study illustrates the increase in resistance of multilayers to multiple modes of cracking that are seen in the monolayer nitride coatings on steel substrates. We provide evidence of the enhanced plasticity, seen as macroscopic bending, which in reality is column sliding in a series of distributed small steps. We discuss the role of misfit dislocations in spreading the material laterally to accommodate the constraints during indentation and lattice bending. Interfacial sliding is seen to reduce the stress concentration by distributing the vertical column sliding and accommodating the flaws generated by the sliding of misaligned column boundaries. Some preferred boundaries with special orientation relations do slide, while near the substrate, the sliding is facilitated by the relaxation in intrinsic residual stresses. An analytical model which was formulated earlier is used to support our experimental findings. Investigations of the plausible reasons for the naturally occurring multilayer mollusc sea shells to reach stiffnesses equal to the upper bound of the rule of mixture value have concluded that its brick and mortar organization is responsible for its exceptional mechanical properties. Inspired by the same model, heat treatment was used to change the architecture of the soft-hard metal/nitride combination from that of the planar interface of the as deposited multilayer to a brick and mortar arrangement. Such an interconnected ZrN microstructure was successfully achieved and the stiffness and hardness were both seen to increase relative to the as received coatings. The possible reasons for this enhancement are discussed in term of this newly emerged architecture ,change in residual stress as well as changes in stoichiometry after heat treatment. The contact damage, though, was found to be more catastrophic relative to the as deposited coating with increased propensities for edge and lateral cracking. This was attributed to the interconnected nitrides formed in the brick and mortar architecture as well as residual stress changes due to the dissolution of Zr in ZrN to form off-stoichiometric nitrides. The cracks feel the presence of the metal and deviate from the otherwise smooth trajectory and take a path along the interface of the metal packet and the interconnected nitride. Summarizing, the present study clearly illustrates the fact that interfaces play an important role in damage control under contact loading. Fracture and deformation are either controlled by metal plasticity, distributing the column sliding in metal/nitride multilayers or by interfacial sliding mediated by interfacial misfit dislocations in case of the nitride/nitride multilayer coatings. The effective role of interfaces is to distribute damage laterally as well as horizontally to relieve stresses and hence enhance the damage tolerance under indentation. Optimum metal layer thickness has been proposed for maximum toughening in the metal/nitride multilayer coating and the role of interfaces in providing modes of plasticity is presented for the nitride/nitride multilayer coatings by use of extensive transmission electron microscopic investigations. A new interconnected architecture coatings provides a unique way of combining stiffness and toughness along with scope for further developing such configurations with improved mechanical properties.

Dissertação de Mestrado Conjunto Europeu em Tribologia de Superficies e Interfaces apresentada à Faculdade de Ciências e Tecnologia
A investigação e desenvolvimento de ligas de titânio tem vindo a ser alvo de estudo durante as últimas décadas devido às suas superiors propriedades físicas, químicas e mecânicas quando comparado com outros ligas. No entanto, o fabrico de components em ligas de titânio é mais caro e requer mais tempo de processamento em comparação com outros metais devido à sua grande dificuldade de maquinar. Uma das principais soluções atualmente usadas para melhorar a maquinação das ligas de titânio é a aplicação de revestimentos na superficie das ferramentas de corte, que por um lado permitem aumentar a vida de ferramenta de corte e por outro melhorar a qualidade da superfície maquinada. Nesta tese, revestimentos industriais depositados em monocamada (TiAlN, TiAlCN) e em multicamada (TiAlN/TiAlCN) foram caracterizados relativamente a diferentes propriedades para determiner quais dos revestimentoa apresentam o melhor compromisso entre propriedades. Os revestimentos depositados foram caracterizados quanto à sua composição química, estrutura, morfologia, resistência à oxidação, estabilidade térmica, propriedades mecânicas e comportamento tribológico à temperatura ambiente. Como esperado os revestimentos apresentam diferentes composições químicas de Ti, Al, N e C devido à diferente composição dos alvos usados e potência aplicadas aos alvos durante a deposição. Todos os revestimentos apresentam uma estrutura fcc. A morfologia dos revestimentos em secção transversal exibem um crescimento columnar, onde o revestimento TiAlN apresenta uma morfologia mas densa do ques os outros revestimentos. O ponto de início de oxidação dos revestimentos é dependente da composição química dos revestimentos: ~900°C, ~850°C e ~800°C para os revestimentos TiAlN, TiAlCN e TiAlN/TiAlCN, respectivamente. Os testes isotérmicos realizados às amostras a 900°C durante 2 h aos revestimentos, promoveram a total oxidação dis revestimentos TiAlCN e TiAlN/TiAlCN, enquanto que o revestimento TiAlN foi apenas parcialmente oxidado. A notável resistência à oxidação do revestimento TiAlN deve-se à formação de uma camada continua e protetora de Al2O3 no topo da camada de óxido. A formação dessa fase foi identificada por difração de raios-x analyses SEM. O revestimento TiAlN/TiAlCN apresentou os maiores valores de dureza – 38 GPa e modulo de elastecidade – 363 GPa, entre os diferentes revestimentos. Após o recozimento, o revestimento TiAlN exibiu um grande aumento de dureza devido ao aumento da sua cristalinidade. Nos testes tribológicos, o coeficiente de atrito, a profundidade de desgaste e a taxa especifica de desgaste corroboram os resultados de dureza e tenacidade. As pistas de desgaste exibem um mecanismo de abrasão, caracterizadas pela presença de ranhuras e detritos. O revestiemnto TiAlN/TiAlCN apresentou o melhor desempenho tribológico devido à combinação de alta dureza e alta tenacidade à fratura em comparação coms outros revestimentos.
The research and development on titanium alloys have been nourishing for quite some time due to their superior physical, chemical and mechanical properties. However, manufacturing titanium is more expensive and requires longer time compared with other metals due to its poor machinability. One of the leading solutions to address the difficulty in machining titanium is to deposit coating on the cutting tools in order lengthen the service lifetime and ensure good quality of machined surface. In this study, industrial made monolithic TiAlN, monolithic TiAlCN and multilayered TiAlN/TiAlCN coatings were thoroughly characterized to determine which coating displayed the best combination of properties. The deposited coatings were fully characterized for their chemical composition, structure and morphology, oxidation resistance, thermal stability, mechanical properties and tribological performance at room temperature. The coatings reported different chemical composition of Ti, Al, N and C due to the different targets, chemical composition and power applied to the target during deposition. All films displayed a fcc NaCl type structure. The SEM micrographs of the cross-section and surface morphology of the as-deposited coatings exhibited a columnar growth with TiAlN showing the densest structure. The onset point of oxidation was measured to be ~900°C, ~850°C and ~800°C for TiAlN, TiAlCN and TiAlN/TiAlCN, respectively. After the isothermal test at 900°C for 2 h, TiAlCN and TiAlN/TiAlCN were fully oxidized while a huge portion of the TiAlN coating still exists. The remarkable oxidation resistance of the latter coating was driven by the formation of a continuous and protective oxide scale Al2O3 on top of the oxide layer. The presence of this oxide scale was confirmed by XRD, SEM micrograph and elemental map distribution. The as-deposited TiAlN/TiAlCN reported the highest H and E values at 38 GPa and 363 GPa, respectively. Upon annealing, TiAlN exhibited a huge increase in hardness due to increase in crystallinity. In the tribological tests, the coefficient of friction, wear depth and wear rate corroborate the hardness and toughness results of the coatings. The wear track exhibit abrasion mechanism which is characterized by grooves and scratches and the presence of wear debris in fish-like form. The multilayered TiAlN/TiAlCN showed the best tribological performance due to the combination of high hardness and high fracture toughness compared to the monolithic TiAlN and TiAlCN coatings.
Outro - Project MCTool21 - POCI-01-0247-FEDER-045940

碩士
國立高雄第一科技大學
機械與自動化工程所
91
In this research, we use the Taguchi method to design experiment procedure. We use separate target when we processed the sputtering. The target material are pure Ti and pure Al, the base material is high-speed steel. The (Ti,Al)CN coating layer is formed by magnetron sputtering. The purpose of this research is to find out the relation between different process parameters and coating film properties such as: surface pattern, microstructure, and mechanical properties etc. Through the study we especially focus on wear capability and try to find out the best process parameters to improve substrate mechanical properties in order to extend the using life. As the results of experiments, we find out such as th follows: 1、 By XRD’s analysis, the (Ti,Al)CN coating film has show the stronger ( 1 1 1 ) peak, lower friction coefficient, good wear-resistance and AlN phase was also shown when substrate bias increased gradually. 2、 The most coating layers have been worn out through wear test results, except the test R8 which was proceed by Ti0.75Al0.25 film compose, 35SCCM C2H2 flow rate, 4SCCM N2 flow rate and –75V substrate bias. And we also get the lowest friction coefficient which 0.203 and the maximum of layer thickness reached to 1.56μm in the test piece R8. 3、 According to the L9 (34) Taguchi experiment results, we have also found the optimum sputtering parameters were : Ti0.75Al0.25 film compose; 40SCCM C2H2 flow rate; 10SCCM N2 flow rate and –75V substrate bias. 4、 The friction coefficient（μ）of coating film is 0.185 when used optimum sputtering parameters by Taguchi confirm experiment. Comparing to high-speed steel substrate （μ=0.5）, it has excellent wear-resistance capability and reduces friction force to improve material using life. 5、 The coating layer’s pressmark is HF3 and it has good adhesive strength (61.53N) by used optimum sputtering parameters. Besides, we also find extremely strong ( 1 1 1 ) X-Ray diffraction peak in the coating layer. To summarize all research results, adopting PVD (Ti,Al)CN coating film could improve high-speed steel wear-resistance capability and mechanical properties to extend material using life.

碩士
明道大學
材料暨系統工程研究所
96
This study used cathode arc evaporation plasma deposition TiAlON thin film. It fixed N2 flow and tune up O2 flow to observe the colours of TiAlON. On any equipment that is used, L*a*b* control can display colours in number format to accurately compare the difference. To pigment properly, nearly hundred layers of coating are usually needed during the process to achieve the desired colours. Therefore, it is significant for the L*a*b control to attain precise colour each time during coating in order to achieve the efficiency. With its high stability, corrosion resistance, wear ability and hardness, vacuum coating is attracting great interest in the decorative-coating industry. The object of this research is to observe the chromaticity as TiAlON thin film is developed and deposited on the brass in Cathode Arc Evaporation System. The oxygen partial pressure applied during the deposition is measured to assist investigating its effect on the phase and chromaticity of TiAlON thin film. Through SEM, EDS, colours meter and optical microstructure, crystal experiment results are processed to analyze thin film morphology composition, microstructure and the colours chromaticity. Results of this study showed that the brightness of thin film will change by tune up O2 flow. If increasing more O2 flow, TiAlON thin film will get more dark, and the contact angle decreasing . After corrosion test, TiAlON thin film has better corrosion resistance than TiAlN.

碩士
大同大學
材料工程學系(所)
94
The work investigated to improve the defect of the bigger particle by Cathodic Arc Deposition (CAD) system with filtered. Because the TiN、TiAlN and TiCN coatings are popularly investigated before. Thereby, in this case, use a Ti target and TiAl target moreover N2 and C2H2 gases are through into with the process parameters to deposited (Ti,TiAl)N and (Ti,TiAl)CN two mixed films. They expect to obtain excellent properties besides to compare with filtered effect. Via knew with the experiment, the filter improves the defect of bigger particle, there are best improvement in roughness (Ra)、adhesion and porosity, moreover the structure cannot change. Also because the porosity decrease to improved with the corrosion resistance. But the particle decrease resulted in the decrease of depositing rate.

碩士
國立中興大學
材料工程學研究所
85
In this research,TiAlN films were deposited on high speed steel( SKH9) by cathodic arc evaporation.The effect of TiAl interlayer on the tribological properties of TiAlN films were investigated. The characteristics of the ternary TiAlNfilms have the properties of high hardness ,abrasion resistance and excellent chemical stability which all contribute to the success of TiN.A graded TiAlN structure is defined as a continuous variation of the various components,fromthe film/substrate interface to the top surface of the film during the growth.The bias voltage applied to the substrate is the primary parameter responsiblefor aluminum depletion and titanium enrichment in the film composition.XRD analysis showed that TiAlN films have strong (111) preferred orientation.Optimized critical load of TiAlN/ SKH9 were obtained at a substrate bias 300v, and with a interlayer thickness of 0.1*10^-6mTiAl.TiAlN graded coating exhibited the highest critical load of 57N while multilayer film measured 51N and singlelayer film measured 47N.The thermal stability of TiAlN film was investigated by TGD. The oxidation resistance of TiAlN exhibited much higher onset temperature of 890C/925C compared to of TiN,TiCN and CrN. This higher oxidation resistance of TiAlN protective layer was conjected to the fact stable Al2O3 atits surface when the coating reaches 600 C - 925 C in air .

When loss of material due to sliding of two solids is promoted/prevented, in the presence of chemically reacting liquid or gas, tribochemical wear is said to occur. Tribochemical wear, in which corrosive media promotes material loss, is a serious concern in a variety of applications like machining, bio-implants, gas turbine engines etc. The most pervasive corrosive media encountered in applications are water and air. Air also contains water vapour along with oxygen, both of which adsorb and react with most materials, thus influencing their wear behaviour. The need for higher operating temperatures and compression ratios in gas turbine engines require development of high temperature wear resistant coatings to protect their soft metallic components. Ti based nitride coatings with Ti, Al, Si, Cr, Ta, Nb, V are known for wear resistance because of their high hardness which is second only to diamond and c-BN. High O affinity of these elements, induce the coatings to form passive oxide scale up to reasonably high temperatures and offer superior corrosion and oxidation resistance. However, sliding can remove the passivating layer, exposing the native surface to the environment which can lead to enhanced tribochemical wear. Oxidation resistance under static conditions does not guarantee low tribochemical wear; however, the tribochemical reactions causing the corrosion are of interest. Another concern is that sliding in unison with high temperatures can activate processes like enhanced diffusion, phase transformations in nitride coatings as well as in the substrate. Hence one of our objectives is to perform wear tests at high temperatures to understand the dominant mechanisms that affect wear in nitride coatings. Wear tests in the range of room temperature up to the oxidation limit of these coatings are designed.In this study TiN and high aluminium containing TiAlN coatings are chosen to study understand the wear behaviour as function of temperature up to 800°C [1]–[3]. In order to study wear of coatings, it is necessary to identify the best possible materials and methods. Though under the targeted application the coatings have to perform under fretting tests, pin on disk configuration is used which simplifies the analysis and gives deeper insight into the wear mechanism. Coated ball is used as the pin which is stationary unlike many earlier studies where the coating is applied on the rotating disk. The purpose of keeping the pin stationary is to minimize the counter-face wear and, instead, accelerate wear in these hard coatings. This method also enables easy and accurate measurement of wear depth and volume by using an optical microscope, while the conventional coated disk method requires profilometry and statistically sound measurements. To enable coating performance, substrate should not undergo much loss of strength before 800°C and hence aerospace grade IN718 alloy is chosen as the substrate which softens slowly beyond 650°C. Alumina is used as counter-face, since it has high hardness, excellent mechanical, chemical and thermal stability. In the current study, TiAlN coating is tested for wear in the range of room temperature to 800°C. Figure 1 represents the data obtained from the wear experiments. It is found that the wear is higher with large scatter at room temperature while it remains constant from 200- 750°C. Two important observations are made, firstly that the TiAlN is susceptible to some kind of a corrosive wear at room temperature which depended on the timing of the tests and secondly that the coating shows a surprisingly constant wear behaviour over the temperature range of 200-750°C. The scatter at room temperature is found to be linked with seasonal fluctuation of humidity which is verified by performing tests under controlled humidity conditions. Water vapour and oxygen are potential reacting gases present in air. Oxidation and oxidative wear is known to occur in many materials as temperatures increase which seem to be linked to thermal activation of oxidation. However lower wear at 200°C and above compared to room temperatures suggests something else to be happening .It is evident then that between room temperature and 200°C lies a transition of some kind in the tribochemical reaction which is responsible for the observed wear behaviour of TiAlN. A detailed study to understand this transition is then undertaken for the composition of TiN coatings so that benchmarking and comparison with TiAlN is possible. Also if the wear behaviour of TiN is found similar to TiAlN then it would indicate a general phenomenon which can be extended to Ti based nitrides. Figure 1 Wear rate as a variation of temperature for TiAlN coatings In contrast to low temperature wear behaviour of TiAlN, a constant wear in the range of 200-750°C is surprising because the primary suspect which is oxidation is thermally activated. The oxide scale though expected to be thin at low temperatures, has to increase in thickness with temperature due to increased diffusion and reaction rates. The oxide scale also undergoes a change in morphology and composition which indicate a lower oxidation resistance as temperature increases. A preliminary characterization of the wear scar on the ball shows that the oxide inside the worn region is thinner than the oxide outside at 750°C. The amount of O within the wear scar is similar to levels observed on as deposited surface while the surface outside the wear scar shows oxidation and discolouration. The results suggest that oxidation inside worn region at high temperatures might be slower than the expected parabolic oxidation occurring outside the wear region. It is speculated that a double layer oxide is formed with TiO2 towards the surface and Al2O3 towards the nitride which is responsible for the lower wear at high temperature. This is supported by the fact that larger amount of Ti is found in the wear debris as temperature inceases. Superficial surface cracks appear at higher loads at temperatures as low as 600°C but they affect wear only above 800°C due to substrate softening. This shows that the coatings are still limited by the substrate softening temperature and could be used at higher temperatures. Tribo-reaction in metals, nitrides and carbides can be brought about in the presence of O2 or water vapour. Tribochemical wear of SiN, SiC, TiN, TiAlN, alumina and most other ceramics at room temperature are found to depend on humidity[4]–[6]. But only tribo-oxidation due to O2 is found to operate at high temperatures[7], [8]. Notwithstanding, it is known that SiC and SiN are more resistant to attack from O2 above 800°C than from steam. Hence the role played by water vapour is found to be convoluted. Moreover, relative humidity is the frequently mentioned quantity with regard tribochemical wear at room temperatures. It should be noted that relative humidity is not a measure of chemical activity of water vapour. Rather the water vapour pressure which represents the chemical activity of water, is not given much importance in the earlier studies. In this study, the importance of humidity, water vapour pressure and temperature in influencing wear, is studied by performing controlled wear tests on TiN. To explore the effect of temperature and water vapour pressure, TiN is tested varying temperature range of 28 °C to 90°C and water vapour pressure in the range of 3-35 mm-of-Hg. Wear tests are conducted keeping temperature constant with varying water vapour pressure and vice versa. The results show that, wear increased with humidity/vapour pressure at a fixed temperature but wear dropped drastically with increase in temperature at constant vapour pressure up to a critical temperature beyond which wear remained constant. This is one of the major unexpected findings since temperature is expected to increase wear volume. Also the critical temperature is found to shift to higher temperatures as water vapour pressures increased. It was suspected that capillary condensation was playing a role in the wear which was later verified. The whole wear behaviour is shown to be correlated with the amount of capillary condensed water. The large radius of curvature of the asperities on the polished coating surface and the smooth surface formed on the counter-face due to debris compaction form conditions favourable for capillary condensation. Any two hydrophilic surfaces which come in contact can form capillary condensation to occur at the cusps formed around the contact. However a threshold pore size of about 1nm existed below which condensation did not influence wear. Another observation is that the water vapour did not affect wear significantly in the absence of condensation for TiN coatings. As temperatures increased condensation became unfavourable, but the high vapour pressure present showed no signs of wear enhancement. This is surprising and unexpected compared to earlier reports.[9], [10] On contrary tests in liquid water showed expected behaviour for tribochemical reaction i.e wear increased with temperature. The wear in liquid water is highest when compared studies in air at any given temperature. The X-ray electron emission spectroscopy (XPS) analysis is performed to understand the surface reactions. It appears that O2 forms a barrier oxide which protects the nitride from reacting with water vapour. However when condensation occurs or in water, the oxygen and water collude into forming softer hydroxide layer which is easily removed. Though chemically water and water vapour are same, they affect wear in TiN very differently. Summarising the synopsis, exploration into high temperature wear of TiAlN reveals that it can handle oxidative wear upto 750°C showing constant wear over the temperature range of 200-750°C. Reduction in residual stresses and substrate softening may be responsible for higher wear at higher loads since the cracking is observed at 5N is absent at 3N. The substrate is expected to soften above 650°C but this does not necessarily affect wear until the load is increased or the temperature is sufficiently high. However TiAlN and TiN coatings showed susceptibility to tribo-corrosion in water and high humidity at room temperature. At high humidity, condensation of water leads to increase in wear. The dependence of wear on humidity is found to be because of capillary condensation. The negligible dependence of wear on humidity in the absence of condensation is ascribed to formation of oxide layer due to reaction with O2 and coating. The oxide barrier formed due to atmospheric O2 protects the coating from reacting with the water vapour. The oxide barrier on TiN forms faster indicating O2 reaction to be faster than the reaction with water vapour. In the presence of capillary condensation or water, O2 is depleted from contacting surfaces thus hindering the formation of the barrier oxide, increasing wear. As temperature increases the condensation becomes unfavourable and barrier oxide dominates the wear mechanism upto high temperatures which is dominated by oxidative wear.

碩士
明道大學
材料科學與工程學系碩士班
100
This thesis is to study the process and properties of the TiAlBN multilayer by using the unbalanced magnetron sputtering system. The content of this study is focused on the microstructure, mechanical properties and its potential application. Two different sputtering systems, home-made and Leybold 600SP were compared with TiAlBN coatings. The process were divided into three sessions, including the synthesis of TiAlB multilayer coatings, which were conducted with the variation of AlB2 magnetron power of 300W, 400W, 500W. The second session is the process with introduction of N2 gas, which leads to TiAlBN multilayer coatings. The third session is carried out by following the second session with extra introduction of C2H2 gas on top formed as TiAlBCN coatings. The Al33B67 and Ti circular targets were face to face installed in the chamber. Microstructures of the studied coatings were examined by XRD for the crystal preferred orientation, SEM for surface morphology and the fractured sections, ESCA for element binding configuration, and AFM. The mechanical properties was investigated by using Rockwell indentation to determine the adhesion, nanoindenter testing for the hardness, the wear test of grinding tungsten steel balls and glass balls. The results show that with increasing magnetron power density contributes to the increase of film thickness. TiAlB and TiAlBN exhibits the low Ra value. Introduction of N2 and C2H2 gases, respectively, leads to the decrease of film hardness, but improve the tribological behaviors.

碩士
國立高雄第一科技大學
機械與自動化工程所
91
Most 3C industry in operation has to meet high precision, high speed and fine dimension demand, the traditional existed cutting tool has it’s limitation . Especially when we processing the P.C. board, the cooling oil is prohibited in order to prevent of creating pollution problem. Therefore cutting tool is easily worn out in this high speed cutting and no cooling oil environment due to temperature increased, which will cost the production cost increase rapidly. In order to meet this requirement, this paper will develop a coated film-TiAlCN which produced by combining two different coated film of TiCN which have high hardness and low friction coefficient, and TiAlN which have high oxidation resistance ability. In this research, we used unbalanced magnetron physical sputtering equipment to sputter TiAlCN coating film on high speed tool steel. We will study the characteristics of TiAlCN coating film to put in use on high temperature process environment. As the result of this experiment, we can found out the oxidation resistance temperature of TiAlCN coating film exhibited onset of 800℃. When the temperature approach 900℃, TiAlCN coating film will not have any protection properties for base material. After that, the base material will oxidation faster, and develop Fe2O3 structure. Beside that, by XRD and EDS analysis, we can found out that because of the carbon element became oxidation easily inside the TiAlCN coating film in the high temperature environment, the hardness and wear resistance will became lower. Until the temperature approach 500℃, it will grown a very thin oxidation film（Al2O3）in the TiAlCN coating film surface. The Al2O3 film has high hardness and high dense structure which coated further avoid oxidation in the inner structure of TiAlCN, and increase the hardness and wear resistance of the TiAlCN in the high temperature environment. Therefore, metastable phase（111）and （200）texture of TiAlCN will transition to （TiN/TiCN/TiAlN/TiAlCN）metastable phase. Finally, we also will discussion the other characteristics such as hardness、adhesive strength、wear resistance and color of the surface of TiAlCN coated film in this paper.

碩士
明道管理學院
材料暨系統工程研究所
93
Abstract In this work, the combinations of metal-doped DLC and TiAlN/TiN double-layered films were designed to deposit on the tool steels using cathodic arc evaporation in a single process. The economic advantage in depositing the combined coating in one production scale PVD coating system is of practical importance. The TiAl-doped DLC as lubricant coatings were synthesized with TiAl-target arc sources to emit ion plasma to activate acetylene reactive gases. Experiments were carried out to deposit TiAl-DLC on TiAlN/TiN/M2 tool steel for different substrate bias ranging from -50 to -200 V, hydrocarbon gases (C2H2) pressure 10 to 25 mtorr and temperature fixed at 180 ℃. Scanning electron microscopy (SEM), Auger electron spectroscopy (AES), micro-Raman spectroscopy. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) techniques were employed to analysis the microstructure properties of TiAl-doped DLC coatings. Vicker's and tribometer tester were used to measure the mechanical properties of TiAl-doped DLC coatings. The results indicated that the bias voltage and hydrocarbon gases (C2H2) pressure plays a major role in the microstructure change in the deposition of TiAl-doped DLC films. The profile ID/IG and sp3/sp2 ratio corresponds to the change of microhardness profile as the bias voltage or the hydrocarbon gases (C2H2) pressure varied. And, TiAl metals are in the form of small nanocrystallites of pure metal or metal carbides dispersed throughout the carbon network. The tribo-analysis indicated that the coatings exhibited steady-state friction in the range of 0.15 - 0.25 to the end of 2 km travel distance. Interesting optimum wear rate corresponded to the steady-state low coefficient of friction of DLC films due to formation of graphitized layer. The lubricity and wear resistance of TiAl-doped DLC coatings is then demonstrated to potentially be applied to the cutting tools with no lubricants. To summary, the optimum condition and properties of TiAl-doped DLC coatings was appeared at the bias of-120 V and the hydrocarbon gases (C2H2) pressure of 15 mtorr.

Etwa 27000 Flugzeuge durchqueren täglich den Luftraum über Europa. Dieser weiter steigende Flugverkehr erfordert neue Richtlinien für die Luftfahrzeuge. Im Besonderen stehen CO2- und NOX-Emission, Kerosinverbrauch und Lärmbelastung unter Optimierungsbedarf. Diese Anforderungen wurden bis 2050 vom Advisory Council for Aerospace Research in Europe (kurz: ACARE) festgelegt und werden wissenschaftlich unterstützt [3, 4]. Um diese Ziele zu erreichen, gibt es verschiedene Forschungsprogramme, Clean Sky ist ein EU-Technologieprogramm davon. In diesem Projekt werden sechs Demonstrator-Programme entwickelt, von denen MTU Aero Engines eines gestaltet. Im Rahmen dieses Projektes wurde eine Weiterentwicklung des Getriebefan (Geared Turbofan-GTF) erreicht, bei dem Fan und Niederdruckturbine durch ein Getriebe voneinander entkoppelt sind. Durch die optimierte Drehzahl beider Komponenten (vergrößerter Fan - langsamer, Niederdruckturbine (LPT) - schneller) wird die Turbinenleistung gesteigert und gleichzeitig die Geräuschemission minimiert. Entwickelt wurde der GTF von Pratt & Whitney in Kooperation mit MTU Aero Engines. Herkömmliche Varianten sehen vor, dass die Niederdruckturbine u.a. den Fan antreibt und zwar nur so schnell, dass der äußere Radius des Fans die zulässige Geschwindigkeit nicht überschreitet. Die herkömmlich verwendeten Nickelbasislegierungen in der Niederdruckturbine haben mit 8 g/cm3 eine zu hohe Dichte um einige Anforderungen im ACARE wirtschaftlich erfüllen zu können. Bereits 1967 hat die US Airforce das große Potential zur Gewichtsreduzierung durch Titanaluminid-Legierungen (TiAl-Legierungen) mit einer Dichte von rund 4 g/cm3 im Hochtemperaturbereich der Flugzeugtriebwerke erkannt. Zwischen 1980 und 1990 entwickelte das General Electric-Forschungscenter die gamma-TiAl-Legierung Ti-48Al-2Cr-2Nb, welche als erste kommerzielle Titanaluminidlegierung in der Niederdruckturbine von Flugzeugtriebwerken eingesetzt wurde. Eine weitere Legierung dieser Werkstoffgruppe kam erst ca. 15 Jahre später zum Einsatz, die TNM-Legierung. Wie man an diesem Beispiel sehen kann, dauert die Integration neuer Werkstoffe in der Luftfahrt aufgrund der notwendigen Vorversuche und Sicherheitsaspekte teilweise 20 Jahre. Seit September 2014 kommt im Triebwerk PW1100G GTF von Pratt & Whitney die geschmiedete Version der TNM-Legierung zum Einsatz. MTU Aero Engines AG München baut hierfür die Niederdruckturbine. Durch die hervorragenden Hochtemperatureigenschaften der gamma-TiAl-Legierungen wie z.B. thermische Stabilität der Mikrostruktur, Resistenz gegen Titanfeuer und hohe spezifische Fes-tigkeit, konnten sich die Titanaluminide in Konkurrenz zu den Nickelbasislegierungen sehr gut platzieren. Deswegen werden die beiden gamma-TiAl-Legierungen (Ti-48Al-2Cr-2Nb, TNMTM) bereits in den letzten Stufen der Niederdruckturbine eingesetzt. Ein Nachteil der gamma-Titanaluminide ist die begrenzte Oxidationsbeständigkeit über 750 °C, wodurch das Einsatzfeld als Hochtemperaturwerkstoff stark begrenzt wird. Um das Anwen-dungspotential der gamma-Titanaluminide weiter zu steigern und auch bei Temperaturen über 750 °C einzusetzen, ist eine Steigerung der Oxidationsbeständigkeit notwendig. Die Oxidationsbeständigkeit kann durch das Aufbringen von Oxidationsschutzschichten wie z.B. Al2O3 erreicht werden. Welche neben der Korrosionsbeständigkeit auch die thermisch-mechanischen Anforderungen des Substrat-Schicht-Verbundes sicherstellen müssen. Zur Erhöhung der Temperaturbelastbarkeit von gamma-TiAl-Schaufeln können zur thermischen Isolation keramische Wärmedämmschichten (WDS) aufgebracht werden. Aufgrund der WDS können höhere Prozesstemperaturen realisiert und die Lebensdauer des Grundwerkstoffs verlängert werden. Die Lebensdauer der Wärmedämmschichten und das Betriebsverhalten werden unter anderem durch eine gute Haftung auf dem Untergrund, eine niedrige Wärmeleitfähigkeit und einen thermisch stabilen Phasenaufbau bestimmt. Die Kombination aus Oxidationsschutz und Wärmedämmung wird bereits für Nickelbasislegierungen in der Brennkammer und Hochdruckturbine der Flugzeugtriebwerke eingesetzt. Um gamma-Titanaluminide in weitere Stufen der Niederdruckturbine oder Hochdruckturbine einzubringen, müssen diese Temperaturen von mindestens 900 °C aushalten und erfordern ebenso Beschichtungen zum Oxidations- und Wärmeschutz. Diese Schutzschichten finden für gamma-Titanaluminide bisher jedoch noch keine Anwendung.