Dissertations / Theses on the topic 'High speed steel properties'

Hot strip mills (HSM) are used to roll cast slabs down from their initial size to plate or sheet, which is then used to manufacture a wide variety of goods for many industrial markets. The working rolls that contact and deform the strip are arguably the primary element of the hot strip mills. The work rolls must have sufficient strength to apply the mechanical force to the strip, while still resisting the wear and thermal stresses inherent to the process. The history of the development of these work rolls spans more than a hundred years. The more recent advancement in work roll technology was the development of High Speed Steel (HSS) work rolls during the 1990's. The HSS rolls utilise a variety of carbide forming elements to improve the wear resistance. The South African Roll Company (SARCO) is an established roll producer and the only one in South Africa with a well-established international client base. SARCO is currently developing a range of high quality HSS rolls and has developed an initial HSS grade, which has shown competitive performance and durability in service compared to established HSS alloys from other roll manufacturers. Although the initial trials show great promise, significant potential for development and associated improvements are available. It has been documented that an additional annealing treatment prior to the regular heat treatment will refine the microstructure of HSS rolls, which should improve mechanical properties and performance. However, although pre-annealing has been documented, the degree of mechanical property improvement associated with the pre-annealing has not been studied and the annealing step does not appear to be commonly applied by roll producers. The first aim of this research project was to investigate the properties of the HSS material currently produced by SARCO to elucidate the source of the combination of high wear resistance and durability. The roll material identified for characterisation consisted of four sets of samples. These were subjected to intensive characterisation, which included chemical analysis, ferrite scope measurements, metallography, hardness testing, Scanning Electron Microscopy (SEM) analysis, X-Ray Diffraction (XRD) analysis and Simultaneous Thermal Analysis (STA). The good combination of performance and durability appears to be the product of the Ni additions, W:Mo ratio, high carbon content, high austenitising temperatures and balanced carbide-former additions. The second objective was to investigate the effect of annealing prior to the typical solution, "soft" quench and tempering heat treatment, on the structure and mechanical properties of the HSS material used for the outer shell of mill rolls. As-cast material was used for the analysis, which was subjected to similar intensive characterisation. High Chromium (HC) used in roll material appears to be more sensitive to both temperature and time variations in heat treatment than HSS. No grain refinement of the HSS material was achieved by the pre-annealing. Higher peak hardness and more gradual reduction in hardness beyond the peak was not found under simulated conditions, indicating that a desired increase in hardness will not be achieved in practice. It was evident that the industrial heat treatment condition cannot be sufficiently simulated by shorter time laboratory tests. The effects of pre-annealing should be researched on lower alloy bainitic HSS material if feasible and the improved wear resistance and toughness benefits of pre-annealing could be quantified by performing industrial trials and fracture toughness testing respectively.
Dissertation (MEng)--University of Pretoria, 2017.
Materials Science and Metallurgical Engineering
MEng
Unrestricted

One of the most important additives in High Speed Steels (HSS) is cobalt, mainly for its effect on the hot properties. Based on statistic data about the increased price of cobalt and its negative effect on human health, an ethical and financial barrier in the steel industry have occurred. In order to solve the problem, it is of great importance to examine the future cobalt price and accessibility, as well as examine the possibility of finding alternative substitutes to cobalt. The purpose of this project was therefore to examine alternatives to cobalt as an alloying element in HSS. A qualitative literature study was performed by analyzing the economy of cobalt, studying the main reasons for cobalts tendency to improve the hot properties of the steel and finding alternative elements to replace, or at least reduce, cobalt in HSS without degrading the hot properties. Cobalt is used both in the chemical and metallurgical business. But the demand of cobalt is largely driven by chemical purposes with the focus on its rechargeable battery applications. The analysis shows that there is nothing pointing at a significant decrease of the price of cobalt. Lithium ion batteries stands for about 50% of current cobalt supply, which is why the price has surged the recent years. The market for electric vehicles and rechargeable batteries has skyrocketed. To decrease the price of cobalt, a substitute for cobalt in rechargeable batteries would need to be found, which is not very likely for the time being. The effect of cobalt in HSS is mainly on the red hardness and tempering resistance. Cobalt increases the bonding strength in the steel matrix and changes the microstructure of the finer secondary carbides. Also the growth rate and coalescence rate of the carbides decreases. This causes the red hardness and the tempering resistance to increase. To replace cobalt, several alternative alloying elements have been researched. Among the most promising are niobium, nitrogen and aluminium, where niobium were found to be of most interest, due to the broad support of relevant articles in the field of powder metallurgical processing. The positive effect of niobium could be regarded as three-fold. The first contribution is the refinement of grain size and homogeneity of the primary carbides, which increases the overall hardness. The second effect is that the addition of niobium shifts the phase equilibria in such a way that the precipitation of primary carbides mainly will be in the form of hard and stable NbC. The majority of the other alloying elements will hence be precipitated as secondary carbides during tempering. The final effect is an increase in secondary hardness, as a consequence of the large amounts of vanadium and smaller amounts of niobium that is being precipitated during tempering to the secondary carbides. This enables a high matrix hardening potential in the optimal state of tempering.

With the desire to improve passenger safety and fuel efficiency, Ultra High Strength Steels (UHSS) have been developed for use in the automotive industry. UHSS are high strength steels with high ductility and strength. DP 980 is one of these UHSS being applied in automobile manufacturing. DP 980 is difficult to join with Resistance Spot Welding (RSW) because of the high carbon content and alloying in this material. The weld becomes brittle when it solidifies during the welding process. With the desire and motivation of widely using UHSS, new welding processes are needed to be developed in order to effectively join DP 980. Friction Stir Spot Welding (FSSW) is a developing welding process aimed to replace RSW in the automotive industry because of its ability to join materials at a lower temperature. Currently the welding loads of the tools are higher than 2000 pounds, ranging from 3,000 to 5,000 pounds, which exceeds the limit of the welding robots in the automotive factories. It is proposed that the welding loads can be reduced by increasing the spindle speed of the FSSW tool. Other focuses in the research include increasing the life of the tool and developing acceptable welding parameters for High Speed FSSW. The experimental work done for this thesis provided support that weld strength can be obtained at levels above the acceptable standard for DP 980 material (greater than 2400 pound lap shear fracture load for 1.2 mm material) while keeping the vertical load on the welding machine spindle below 2000 lbs.

Aircraft are often designed with numbers determined by testing in a lab, rather than by repeatedly building prototypes. These lab tests conform to testing specifications so that the numbers can be compared between manufacturers, suppliers, and lab technicians. One such specification is ASTM specification E238 – 84(08), and it is used to determine important properties of a bearing pin joint like hinges, bolt holes, and rivet joints. The properties determined from this fastener-through-plate method are bearing strength, bearing yield strength, and bearing stiffness. Adhering to the methods outlined in ASTM E238, a study was performed, looking at the effects that plate material, fastener used, fastener lubrication, and plate hole preparation method (whether drilled and reamed or just drilled) have on the three bearing joint properties. The plate materials used were Al 7050 – T7451, Ti – 6Al – 4V (mill annealed), and PH13 – 8Mo – H1000. The fasteners were Ti – 6Al – 4V screws, coated A286 screws, and high speed steel (HSS) pins used as a control. Lubrication was tested using a corrosion inhibitor, PR – 1776M B – 2 from PRC – DeSoto, on the fastener or leaving the fastener uncoated. The HSS pins were always tested in the uncoated condition. 54 runs were performed, as outlined by a D-optimal design of experiment. It was discovered from the statistical analysis of the results via ANOVA that both the plate material used and the pin material, whether a screw or a pin, had a significant effect on the bearing strength, bearing yield strength, and bearing stiffness. The interaction between the two factors was also significant on all responses but the bearing stiffness. PH13 – 8Mo – H1000 plates seemed to perform best on average, followed by Ti – 6Al – 4V plates, then Al 7050 – T7451 plates. PH13 – 8Mo – H1000 and Ti – 6Al – 4V plates had similar bearing strength and bearing yield strength averages with the HSS control pins being used, which had the highest mean values for a given plate and fastener. The Ti – 6Al – 4V and A286 screws behaved and performed statistically similar in most cases, except when hole preparation method was take into account. The Ti – 6Al – 4V screws performed better when the hole was drilled and reamed, while the coated A286 screws performed better when the hole was drilled only. All screws had lower resulting bearing properties than the HSS control pins. It was also found that ASTM specification E238 – 84(08) is a precise test method, since the method could be performed repeatably and reliably with no missing data points. Therefore, this ASTM testing method is reasonable for determining bearing properties, which can then be used to design aircraft.

There is an interest in industry in cost reduction. Tool wear constitutes an important element in the cost of many metal working processes, not only because of the cost of the tool, but also because of the cost of machine downtime. Saltbath nitriding of high speed steel tools adds only about 1% to the cost of a finished tool, but has been found to confer benefits considerably in excess of this over a range of cutting conditions . A series of cutting tests is described, during which cutting forces and tool temperatures were recorded simultaneously using microcomputer based instrumentation developed at the Polytechnic as part of this study. The shear mechanism for tools with a nose radius is investigated, and methods for evaluating the primary shear plane area are proposed and discussed. The variation in primary shear plane area with chip flow angle is evaluated. The method for predicting chip flow angle from tool geometry is presented, and results from this analysis compared with experimental data . A method for predicting primary shear angle from tool geometry, force measurements and workpiece material properties is developed. A number of methods for measuring tool temperature are described . Temperature distributions obtained from finite element heat transfer analysis are presented, and a mechanism for the catastrophic failure of the toolnose is proposed. A range of cutting conditions is described, over which the performance of high speed steel cutting tools is enhaced by saltbath nitriding.

A detailed study has been made of commercially produced, powder metallurgy, BT42 grade high speed steel (H.S.S.) indexable cutting tool inserts coated with a thin layer of titanium nitride (TiN) by chemical vapour deposition (C.V.D.). The characteristics of the coating before and after the obligatory substrate heat treatment were first ascertained using various techniques including X-ray diffraction, Auger electron spectroscopy, fractography, scanning and transmission electron microscopy, microhardness testing, profilometry, optical microscopy and scratch-adhesion testing. It was found that the characteristics of the TiN coating were not significantly affected by the substrate heat treatment and that they were comparable to those presented in the literature for similar C.V.D. coatings on cemented carbide inserts. The cutting properties of the fully characterised TiN coated H.S.S. inserts were then compared to those of uncoated inserts in a series of turning tests on 817M40 workpiece material, carried out under conditions of built-up edge (b.u.e.) formation at cutting speeds in the -1 range 30-60 m min. Comparison of the inserts with regard to tool life, tool wear, tool forces, apparent coefficient of friction, b.u.e. formation and workpiece surface finish, revealed that the TiN coated inserts had significantly improved cutting properties relative to the uncoated inserts. Additional tests showed that increasing coating thickness led to further improvements in cutting performance. The role of the TiN coating was studied from metallographic sections through worn inserts, and the reasons for its significant effect on the cutting properties of tbe H.S.S. inserts are discussed. Similar inserts coated with TiN by physical vapour deposition (P.V.D.) were also characterised and their cutting performance determined. The results obtained are compared to those for the C.V.D. TiN coated inserts. Differences in the cutting performance are related to the different characteristics of the two coatings arising from the processes used for their deposition.

High speed machining was developed over sixty years ago and at present is still limited to just a few materials, these being aluminium and its alloys, hardened steels for the mould and die industry and titanium for aerospace applications. Recently there has been additional work in high speed machining on some of the more exotic aerospace alloys such as inconel and nimonic alloys. This thesis addresses the problems encountered when machining high chromium/nickel steel alloys that are part of the stainless steel family. Three grades of stainless steel were selected for this purpose, these being a martensitic grade (416) and two austenitic grades (303 & 316). These materials were high speed milled at cuttinspeeds of up to 3,000 m min-1, via the use of two machining methodologies; high torque-low speed and low torque-high speed milling. High torque-low speed milling was accomplished through the use of specially designed large diameter dual-plane balanced face mills, that when rotated at 6,000 rev mon-1 generated a cuting speed of 3,000 m min-1. These cutters were capable of machining three grades of stainless steel at approximately ten times that of the cutting speeds normally selected for materials that are cut conventionally. However, at the elevated cutting speeds machining of the two austenitic grades of stainless steel exhibited high tool wear rates which contributed to both poor surface finish and high cutting forces.The lo torque-high speed machining of these stainless steel grades was undertaken via specifically designed variable axial rake angle cutters in conjunction with a gear-driven speed increaser. This head gave a maxiumum cutting speed of 750 m min-1 when the cutters were rotated at 20,000 rev min-1. Experiments indicated that the three grades of stainless steel could be machined at high rotational speeds, with good surface finish produced with negative axial rake angled tools. This machining strategy caused tool 'ironing' of the machined surface. cutting forces were lower at all cutting speeds when a positive axial rake angled tool was employed, although at elevated cutting speeds tool wear was excessive regardless of any axia rake angle geometry.

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 90-92).
We explore a non-contact method to measure changes in fluid properties by analyzing refractive motion in high speed video. We present a method of extracting fluid properties by performing video motion analysis using an automated wavelength matching filter followed by fitting of the measurements to theoretical capillary-gravity wave dispersion equations. This method requires an understanding of how field of view, refraction, and parallax affect measurements. We tested the method by analyzing trends in the surface tension to density ratio for cooling water, and for water versus glycerol.
by Victoria Allyce Gunning.
M. Eng.

Arc welding is the most widely used set of joining technologies in industry today. The automotive tier supplier network and light manufacturing are significant users of arc welding, particularly gas metal arc welding (GMAW) and pulsed GMAW (GMAW-P). For sheet metal welding the majority of welds are single pass fillet welds on T-butt, lap, or edge joints. A fundamental problem and limitation to the use of higher travel speeds in GMAW is the phenomenon of weld bead humping, a weld profile defect with a wavelike profile to the weld bead that has peaks and troughs in the longitudinal direction.

The oxidation behaviour of high speed steel (1.55 % C, 7.70 % Cr, 4.90 %V, and 2.00% Mo) was studied isothermally at 550 and 615'C for three different environmental conditions, two of which consisted in a mixture of dry air and water vapour flowing at a rate of 0.45 or 1.45 cm'/min respectively, compared to dry air conditions. At 615'C and for the maximum water vapour content, the oxidation behaviour was initially logarithmic followed by linear stage. In contrast, for a water vapour flow rate of 0.45 CM3/Min, the oxidation was parabolic, which resulted in a greater mass gain of the samples after I hour oxidation, even though there was a lower water content. This was believed to be related to the partial pressure of oxygen and therefore to the amount of oxygen available for oxidation. When exposed to dry air, logarithmic kinetics were observed, with much lower mass gain compared with the other two environmental conditions. Reducing the test temperature to 550'C only reduced the mass gain, with the same oxidation kinetics for each condition, suggesting the same oxidation mechanisms at both temperatures. For the humid conditions, an iron-chromium spinel (Fe, Cr)304was formed along with magnetite Fe304 and hematite Fe203- In dry conditions the spinel and hematite were also present. In addition, a VO vanadium oxide layer was located at the top of the oxide layer, indicating oxidation of the MC vanadium rich carbides, promoted by the high partial pressure of oxygen of the environment. The steel was also exposed to cyclic temperature fluctuations, of two different frequencies, in an attempt to more closely simulate the conditions found during operation of rolls in industry. For the high frequency tests, it was difficult to establish a mathematical relationship for the oxide growth, with the kinetics being rather stochastic. The cyclic oxidation produced a very thin granular layer which appeared to be the spinel (Fe, Cr)304. Local surface regions exhibited high plastic deformation associated with cracks that facilitated the oxygen dissolution within the steel. In the low frequency cyclic tests, the oxidation kinetics were parabolic at both test temperatures. Quenching in water, resulted in the preferential spallation of the hematite by a mechanism known as "buckling", generated from compressive thermal stresses. Material was removed at a rate of -0.13mg/cycle and -0.07mg/cycle at 615 and 550'C respectively, leaving the surface only protected by a layer of iron-chromium spinel. The relationship between the wear of the high speed steel and oxidation was investigated at 600,500 and 4001C in a rolling-sliding disc on disc configuration using a 2.5 kg load for a sliding distance of III km for two different environmental conditions (water, both gaseous and liquid, and laboratory dry air). The specific wear rate of the high speed steel discs was greater for the dry tests compared to the wet ones. However, the specific wear rate of the dry tests was strongly temperature dependent, while for the wet tests, the wear rate was insensitive to temperature. The dry tests exhibited a combination of metallic and oxidational wear, while the wet tests were almost entirely oxidational, with a different oxide phase constitution to the dry tests. Surprisingly, the wet tests exhibited higher friction compared to the wet tests. The reasons for this and the difference in wear rates are discussed and compared to the static oxidation tests.

A detailed study has been made of the atmospheric pressure chemical vapour deposition (CVD) of aluminium oxide (Al2O3) coatings on powder metallurgy (PM) BT42 grade high speed steel (HSS) indexable cutting tool inserts. To facilitate this, a laboratory-scale CVD reactor was initially designed and purpose-built. The literature on the effect of process parameters on Al203 coatings chemically vapour deposited on cemented carbide substrates was comprehensively surveyed. With reference to deposition conditions quoted in this literature, a series of trial Al203 coating runs were then performed using uncoated and TiN, TiC and Ti(C1N) precoated PM HSS inserts. Concurrently, modifications to the laboratory-scale CVD reactor were made. Eventually, deposition conditions were established under which a preliminary a Al203 coating could be deposited on the PM HSS inserts and, in the case of the Ti(C1N) precoated inserts only, substantially retained during the obligatory post-coating HSS substrate heat treatment. The effect of the absence/presence and type of precoating on the CVD of AI203 coatings on the PM HSS inserts are discussed. Subsequent coating runs were carried out only on Ti(C1N) precoated inserts. The characteristics of the preliminary AlP, coating on the Ti(C1N) precoated PM HSS inserts were determined, both before and after the obligatory HSS substrate heat treatment, using an established characterisation procedure. This involved the following techniques: X-ray diffraction, Auger electron spectroscopy, optical microscopy, fractography, scanning electron microscopy, microhardness testing, profilometry and scratch-adhesion testing. Although many of the characteristics of the preliminary AI20, coating were found to be inferior to those presented in the literature, they were also established to be essentially unaffected by the post-coating HSS substrate heat treatment. To im prove upon the preliminary Al203 coating, the effect of two of the most important CVD process parameters quoted in the literature; C02JH 2 mole ratio and Alel3 concentration, on the characteristics of Al20, coatings chemically vapour deposited on the Ti(C1N) precoated PM HSS inserts was investigated. Both parameters were found to have a significant effect on Al203 coating characteristics. The reasons for this are discussed in detail.

With the desire to lighten the frame while keeping or increasing the strength, Advanced High-Strength Steels (AHSS) have been developed for use in the automotive industry. AHSS meet many vehicle functional requirements because of their excellent strength and acceptable ductility. But joining AHSS is a challenge, because weldability is lower than that of mild steels. Friction stir spot welding (FSSW) is a solid state joining process that can provide a solution to the weldability issues in AHSS, but FSSW has not been studied in great detail for this application. In this work, Si3N4 tools were used for FSSW experiments on DP 980 steel with 1.2mm thickness. Joint strength was measured by lap shear tension testing, while thermocouples were used for the temperature measurements. A finite element model was developed in order to predict material flow and temperatures associated with FSSW. Since a 3D model of the process is very time consuming, a novel 2D model was developed for this study. An updated Lagrangian scheme was employed to predict the flow of sheet material, subjected to the boundary conditions of the fixed backing plate and descending rotating tool. Heat generation by friction was computed by including the rotational velocity component from the tool in the thermal boundary conditions. Material flow was calculated from a velocity field while an isotropic, viscoplastic Norton-Hoff law was used to compute the material flow stress as a function of temperature, strain and strain rate. Shear stress at the tool/sheet interface was computed using the viscoplastic friction law. The model predicted welding temperatures to within 4% of the experiments. The welding loads were significantly over predicted. Comparison with a 3D model of FSSW showed that frictional heating and the proportion of total heat generated by friction were similar. The position of the joint interface was reasonably well predicted compared to experiment.

Thesis (M.S.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 14, 2008) Includes bibliographical references.

Thesis: S.M. in Engineering Systems, Massachusetts Institute of Technology, School of Engineering, Institute for Data, Systems, and Society, 2016.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 221-224).
High-Speed Rail (HSR) has been expanding throughout the world, providing various nations with alternative solutions for the infrastructure design of intercity passenger travel. HSR is a capital-intensive infrastructure, in which multiple subsystems are closely integrated. Also, HSR operation lasts for a long period, and its performance indicators are continuously altered by incremental updates. With this background, design and monitoring of lifecycle properties, or "ilities", is an important factor to achieve long-term successful operation. This thesis aims to analyze and evaluate dynamic behaviors of "ilities" and their interactions in HSR operation. After the literature review and the study of industrial trends about HSR "ilities", safety, availability and profitability are chosen as key "ilities" which should be monitored in HSR operation. The Tokaido Shinkansen in Japan, and Amtrak's service in the US Northeast Corridor (NEC) are chosen as cases to study "ilities" trends. In the Tokaido Shinkansen, three "ilities" form a positive feedback loop to make HSR operation successful. The NEC shows high profitability, but it does not perform as well in terms of safety and availability due to several systemic factors. System Dynamics (SD) is applied to visualize interactions of "ilities" and other variables of interest. Qualitative causal loop diagrams (CLD) reveal several feedback loops affecting "ilities". In particular, the integration of train operation and infrastructure / rolling stock management results in the emergence of major feedback loops which cannot easily be captured by other methodologies. Qualitative SD models are converted into quantitative SD models, and numerical simulations are run to further understand the structure of causal loop diagrams. Estimated parameters in the Tokaido and the NEC suggest the different relationships among "ilities" and other variables. Further, sensitivity analyses are conducted to evaluate how different policies affect "ilities" in future HSR operations.
by Tatsuya Doi.
S.M. in Engineering Systems

A detailed study has been made of titanium carbide (TiC) coatings chemically vapour deposited on powder metallurgy (PM) BT42 grade high speed steel (HSS) indexable cutting tool inserts, in collaboration with Edgar Allen Tools, Sheffield. Initially, the characteristics of a TiC coating deposited under the standard conditions employed by Edgar Allen Tools were determined, both before and after the obligatory HSS substrate heat treatment. This was done using various techniques including x-ray diffraction, scanning electron microscopy, micro-hardness testing, profilometry, optical microscopy and scratch-adhesion testing. Although the characteristics of the TiC coating were found not to be significantly affected by the HSS substrate heat treatment, some of them were different to those presented in the literature for TiC coatings chemically vapour deposited on cemented carbide substrates. A comprehensive survey of the literature revealed that the process parameters employed during the chemical vapour deposition (CVD) of TiC coatings, particularly the CHy/TiCly mole ratio and deposition temperature, have a significant effect on coating characteristics. Consequently, it was decided to investigate the effect of these parameters on the characteristics of the TIC coatings chemically vapour deposited on the PM HSS inserts and, further, their effect on the tool lives exhibited by the coated inserts. The latter were determined from a series of turning tests on 817M40 workpiece material, carried out under conditions of builtup- edge (bue) formation, at cutting speeds in the range 37.5 - 60 m min 1. Both process parameters were found to have a marked effect on the characteristics of the TiC coatings and on the tool lives exhibited by the coated inserts. The reasons for this are discussbd. The TiC coated inserts which displayed the most favourable combination of coating characteristics and tool life were used in two further series of turning tests carried out to investigate tool wear, bue size, tool forces, apparent coefficient of friction and workpiece surface finish. Uncoated inserts were also tested. The application of the TiC coating was found to have led to a marked improvement in the cutting properties of the PM HSS inserts. Its role during cutting was studied from metallographic sections through worn inserts and the reasons for its effect on cutting properties are discussed.

Thesis (M.S.)--Worcester Polytechnic Institute.
Keywords: product geometry; hot rolling; high speed rolling; rolling simulation; bar and rod rolling; free surface; finite element analysis. Includes bibliographical references (p. 69-75).

For many materials and components like in high speed trains and airplanes fatigue failures occur in the range of over 107 load cycles which is called the high cycle fatigue range. A modern version of the springs was invented which are applied in a certain application. Ultrasonic fatigue testing (20 kHz machine) was conducted for evaluating the steel of the springs. This research explores the fundamental understanding of high cycle fatigue testing of strip steel and assesses a stainless martensitic chromium steel at the high cycle fatigue range. Finite element modeling was conducted to gain knowledge about the effect of various parameters. Significant attention was devoted to the fatigue failure initiations by SEM/EDS. The work demonstrated that the method of investigation for high cycle fatigue test is reliable. Fatigue failure at this range was initiated by internal defects which all included non-metallic inclusion. A critical distance was defined Within the strip fatigue specimen where all the fatigue failure initiated. The 3D stress field in the specimen was determined by FEM modeling and the local applied stress at the whole of the flat part of specimen and critical distance was estimated. FEM was also employed to give additional information about the effect of parameters. It was established that damping had the largest influence. The local applied stress of the fatigue test was calculated by means of FEM and SEM analysis. It was used to adjust the S-N curve which resulted in 15% lower values than the nominal applied stress.

The objective of this dissertation is to analyse the performance of a linear induction motor suitable to drive a circular saw blade. A selection of analytical methods available from the field of electrical machine theory was used to investigate the particular type of motor. The theoretical analysis is supported by an extensive experimental investigation. Although LIMs have been designed, analyzed and applied in other applications, significant differences exist between those LIMs and the one used for the new application. These include: the annular shaped motor, the smaller air gap, and the rotor which is thin and made of steel. Because of these differences, the methods used by previous investigators were not sufficient to design the LIM required. The theoretical analysis used a selection of methods described in the literature to quantify the effect of the rotor material, the end effect and the edge effect. New methods are described to analyse the effect of the annular shape, the normal forces on the rotor and the coil connection. In addition, a new consideration in the optimisation of these type of motors is described. An extensive experimental program was undertaken. Six different linear motors were constructed with output powers ranging from one to fifty kWatts. In addition, inverters, dynamometers, flux measurement apparatus, speed measurement, thrust measurement and friction measurement apparatus were designed and constructed. The effects on performance of slot harmonics, winding connections, the end effect and the edge effect were measured. Several contributions to the field of electrical machine theory are presented. The first is a new annular disc motor resistivity correction factor. Second, is the analysis of the effects of poles in parallel versus in series in linear induction motors. Third, is the experimental comparison between odd and even pole designs. The fourth is a second optimum goodness consideration for LIMs, which had not previously been considered. The fifth is the analysis of the rotor/stator attractive force for magnetic rotor double sided motors and a description of the flux (crenelated flux) which causes the force. Finally, a criterion for when the re-entry effect may occur is presented.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

The high speed deformation behavior of a commercially available dual phase (DP) steel was studied by means of split Hopkinson bar apparatus in shear punch (25m/s) and tension (1000s-1) modes with an emphasis on the influence of microstructure. The cold rolled sheet material was subjected to a variety of heat treatment conditions to produce several different microstructures, namely ferrite plus pearlite, ferrite plus bainite and/or acicular ferrite, ferrite plus bainite and martensite, and ferrite plus different fractions of martensite. Static properties (0.01mm/s for shear punch and 0.001s -1 for tension) of all the microstructures were also measured by an MTS hydraulic machine and compared to the dynamic properties. The effects of low temperature tempering and bake hardening were investigated for some ferrite plus martensite microstructures. In addition, two other materials, composition designed as high strength low alloy (HSLA) steel and transformation induced plasticity (TRIP) steel, were heat treated and tested to study the effect of alloy chemistry on the microstructure and property relationship.
A strong effect of microstructure on both static and dynamic properties and on the relationship between static and dynamic properties was observed. According to the variation of dynamic factor with static strength, three groups of microstructures with three distinct behaviors were identified, i.e. classic dual phase (ferrite plus less than 50% martensite), martensite-matrix dual phase (ferrite plus more than 50% martensite), and non-dual phase (ferrite plus non-martensite). Under the same static strength level, the dual phase microstructure was found to absorb more dynamic energy than other microstructures. It was also observed that the general dependence of microstructure on static and dynamic property relationship was not strongly influenced by chemical composition, except the ferrite plus martensite microstructures generated by the TRIP chemistry, which exhibited much better dynamic factor values. This may suggest that solid solution strengthening should be more utilized in the design of crashworthy dual phase steels.

With the increasing environmental impact from the automotive industry, electric vehicles become more and more popular. This combined with the great breakthroughs in fast electronics the switched reluctance motor (SRM) has again gained popularity in recent years. Due to its cheap and rugged construction it is a good alternative to the permanent magnet motors and to the induction motor. The ́two main problems holding the SRM back are torque ripple and the acoustic noise generated from it. A lot of research is currently being performed in order to find a solution to these issues. This thesis has investigated different materials for the rotor in a high speed SRM. Different materials have been evaluated based on both mechanical and magnetic properties. This is done through simulations of the forces acting on the rotor combined with simulations of the magnetic field. The forces are simulate in the DASSULT SYSTEMS ABAQUS program and the magnetic field is simulate using AVL FIRE. Three different kinds of alloys are investigated, two different cobalt alloys are simulated as well as a silicon alloy with pure iron as a reference. The results show that the material needs to have a yield strength of at least 349 MPa to withstand the forces affecting the rotor. And that by using the high purity cobalt-iron alloy the generated torque could be increased with up to 20.9%, but with a cost increase of 3151.9% compared to the silicon alloy.

The high temperature, high pressure electrochemical behavior of A516 Gr. 70 carbon steel in aqueous alkaline sulfide solutions was studied by means of polarization tests and cyclic volt-ammetry. The effects of variation of temperature (90-150°C), sulfide concentration (0-3 m), scan rate (1-50 mV/s) and scan range, and the effects of stirring and polarization at the switching potentials between scans were investigated. Passivation was consistent with formation of a protective Fe₂O₃ film. An understanding of the electrochemical behavior of iron in the alkaline sulfide solutions was facilitated by the construction of E-pH diagrams for S-H₂0 and Fe-S-H₂O systems at 25, 100 and 150°C. Sulfide, S²-, currently considered to be stable only at extremely high pH, was excluded from the E-pH diagrams. Reference electrodes, compatible with sulfide solution, were designed for use with an autoclave. The response of the Ag/Ag₂S electrode (SSSE) to variation of temperature, sulfide and hydroxide concentration, and chloride addition was studied. Liquid junction potential and thermal liquid junction potential corrections were applied. The SSSE was not reliably predictable thermodynamically, but was stable and was proven effective in the polarization study. The electrochemical potentials of inert metal reference electrodes, Hg and Pt, were found to be consistent with the mixed potential between polysulfide Sײ⁻, and thiosulfate, S₂O₃²⁻. The Tafel slopes from anodic polarization curves of Pt in alkaline sulfide solutions were consistent with oxidation of HS⁻ to S₂0₃²⁻ at the mixed potential. At more noble potentials, oxidation to polysulfide occurred. Reaction path mechanisms were proposed. Understanding of sulfide oxidation aided in interpretation of the electrochemical behavior of steel in the alkaline sulfide solutions.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

This research aims to analyse the dynamic behaviour of Soil-Steel Composite Bridges when subjected by high-speed trains. the analyses of the dynamic response for these structures are needed since there is little research performed in the present field of knowledge. Since there is also in need to perform separate dynamic analysis for these structures to verify their dynamic response, the dynamic behaviour must be analysed. The research are performed in 2D FE-models in the commercial FE-program Brigade/PLUS since there is of interest to analyse if simplified 2D-models can predict the dynamic behaviour for these structures and verify against design criterions in regulatory documents. The research is performed by calibrating a reference model against collected field measurements from a constructed Soil-Steel Composite Bridge, SSCB, located in Märsta, Sweden, Märsta Bridge. The calibration process was made to ensure satisfactory results before continuing the research by analysing a future planned SSCB in a case study that is known to in the future be subjected by high-speed trains. The future planned bridge is the Björnbo Bridge located in Skutskär, Sweden. A static structural design is first made with existing methods to verify Björnbo Bridge for static load cases. Attempts is made to verify the Björnbo Bridge against dynamic criterions available in Eurocode documents and Swedish Transport Administration regulatory documents, which includes verifying accelerations limits for 10 different high-speed trains. Smaller analysis of fatigue for the Märsta Bridge and the Björnbo Bridge was also made to verify dynamic stresses from giving fatigue damages. Since the research is limited for SSCB for dynamic cases, parametric studies are performed for certain parameters identified from an international literature review of earlier studies in both static and dynamic analysis. The studied parameters are: Soil cover depth, Young's modulus for engineered backfill and different profiles impact. These parametric studies are made to be able to understand influence and sensitivities from the analysed parameters with the long-term goal to develop analysis methods and verifications for SSCB for dynamic load situations. The calibrated reference model showed that there are difficulties in calibrating acceleration levels that agrees with the field measurements from Märsta Bridge. The expected result from the analysis of the Björnbo bridge was to fulfil static structural design criterions and that the acceleration limits were below serviceability criterions for dynamic analysis according to Eurocode documents. Moreover, that the stresses did not give fatigue damages. From parametric studies, it has shown that the governing parameter is the Young's modulus for engineered backfill, which affects estimated accelerations in a fashion that was not expected in the beginning. The presumption to perform dynamic analysis with 2D FE-models has shown that all aspects that is needed to verify cannot be performed, such as bending in two directions or twisting mode shapes. Thus, there is in need to find ways to perform dynamic analysis for SSCB with efficient 3D-models.
Denna avhandling syftar till att undersöka det dynamiska beteendet hos rörbroar när dem belastas med höghastighetståg. Analyser av den dynamiska responsen för dessa konstruktioner är behövlig då det finns lite forskning som utförts inom kunskapsområdet. Då man även behöver genomföra separata dynamiska analyser för dessa konstruktioner för att verifiera  deras dynamiska beteende, så är det ett behov av att dess dynamiska beteende analyseras. Undersökningen är genomförd med FE-modeller i 2D i det kommersiella FE-programmet Brigade/PLUS då det är av intresse att analysera om förenklade 2D-modeller kan forutse det dynamiska beteendet för dessa konstruktioner och verifiera konstruktionen mot kriterier ställda i styrande dokument. Undersökningen genomförs genom att kalibrera en referens modell mot insamlade fältmätningar från en konstruerad rörbro i Märsta, Sverige, Märsta rörbro. Kalibreringsprocessen genomförs för att försäkra att godtagbara resultat erhålls innan undersökningen fortsätter med att analysera en planerad rörbro i en fallstudie som kommer belastas av höghastighetståg. Den planerade rörbron är Björnbo rörbro som skall konstrueras i Skutskär, Sverige. En statisk konstruktionsberäkning med befintliga metoder är först utförd för att erhålla dimensioner och verifiera Björnbo rörbro för ett statiskt lastfall. Därefter utförs försök att verifiera Björnbo rörbro mot dynamiska villkor tillgängliga i Eurokod och Trafikverkets styrande dokument, detta inkluderar att verifiera accelerationsnivåer för 10 olika höghastighetståg. Mindre analyser genomförs även för utmattning för Märsta rörbro och Björnbo rörbro för att verifiera den dynamiska spänningshistoriken inte orsakar utmattningsskador. Då forskningen är begränsad gällande dynamiska studier för rörbroar, så utförs även parametriska studier för parametrar identifierade från en internationell litteraturinventering av tidigare studerade fall för rörbroar gällande både statiska och dynamiska analyser. Dom studerade parametrarna är: Överfyllnadshöjd, Jordmodul för kringfyllning och olika profilers inverkan. Dessa parametriska studier är utförda för att förstå influensen och känsligheten i dessa parametrar med det långsiktiga målet att utveckla analysmetoder för att verifiera rörbroar även för dynamiska situationer. Den kalibrerade modellen visade att det var svårigheter att kalibrera in accelerationsnivåer som överensstämde med fältmätningar från Märsta rörbro. Det förväntade resultatet från Björnbo rörbro var att uppfylla statiska konstruktionsvillkor och att uppfylla accelerationskrav för bruksgränstillståndet för konstruktionen. Samt att kunna verifiera att utmattningen inte skulle utgöra ett problem. Från dom parametriska studierna så har det visat att den styrande parametern är jordmodulen för kringfyllningen, den påverkar accelerationsnivåer som inte var förväntat vid undersökningens påbörjan. Antagandet att utföra de dynamiska analyserna med 2D FE-modeller har visat att alla aspekter som ska verifierasinte kan utföras, så som böjande moment i två riktningar eller vridande mod former. Således, så finns ett behov av att finna vägar att utföra dynamiska analyser för rörbroar i effektiva 3D-modeller

The effects of variations in alloying content on the microstructure and mechanical properties of high strength steel weld metals have been studied. Based on neural network modelling, weld metals were produced using shielded metal arc welding with nickel at 7 or 9 wt. %, manganese at 2 or 0.5 wt. % while carbon was varied between 0.03 and 0.11 wt. %. From mechanical testing, it was confirmed that a large gain in impact toughness could be achieved by reducing the manganese content. Carbon additions were found to increase strength with only a minor loss to impact toughness as predicted by the modelling. The highest yield strength (912 MPa) in combination with good impact toughness (over 60 J at -100 °C) was achieved with an alloying content of 7 wt. % nickel, 0.5 wt. % manganese and 0.11 wt. % carbon. Based on thermodynamic calculations and observed segregation behaviour it was concluded that the weld metals solidify as austenite. The microstructure was characterised using optical, transmission electron and high resolution scanning electron microscopy. At interdendritic regions mainly martensite was found. In dendrite core regions of the low carbon weld metals a mixture of upper bainite, lower bainite and a novel constituent - coalesced bainite - formed. Coalesced bainite was characterised by large bainitic ferrite grains with cementite precipitates and is believed to form when the bainite and martensite start temperatures are close to each other. Carbon additions were found to promote a more martensitic microstructure throughout the dendrites. Mechanical properties could be rationalised in terms of microstructural constituents and a constitutional diagram was constructed summarising microstructure as a function of manganese and nickel contents.

Unter den verschiedenen additiven Fertigungsverfahren stellt das selektive Laserschmelzen (SLM) eine optimale Technologie für die Herstellung von metallischen Bauteilen mit komplexen Geometrien und hervorragenden Eigenschaften dar. SLM-Bauteile werden Schicht für Schicht mit hochenergetischen Laserstrahlen hergestellt, was das SLM flexibler als konventionelle Produktionstechnologien wie das Gießen macht. Die beim SLM auftretenden schnellen Aufheiz-/Kühlraten können zu deutlich unterschiedlichen Gefügen im Vergleich zu herkömmlichen Herstellungsverfahren führen. Die beim SLM entstehenden Hochtemperaturgradienten können sich weiterhin positiv auf die Gefügeentstehung (Phasenbildung, Morphologie, …) und damit auf die mechanischen Eigenschaften der SLM-Bauteile auswirken. Darüber hinaus können die mit SLM gefertigten Teile mit der Notwendigkeit einer minimalen Nachbearbeitung in den Einsatz genommen werden. Bisher wurden mehrere Studien zu den Parametern: Optimierung oder Verarbeitung von Verbundwerkstoffen mit fehlerfreien Teilen durchgeführt Die Scanstrategie hat dabei einen besonders großen Einfluss bei der Materialbearbeitung durch die additive Fertigung. Die Optimierung der Scanstrategie ist daher von zentraler Bedeutung für die Synthese von Materialien mit verbesserten physikalischen und mechanischen Eigenschaften. Diese Arbeit untersucht die Wirkung von vier verschiedenen Scanning-Strategien auf das Gefüge und das mechanische Verhalten von 316L Edelstahl, synthetisiert durch selektives Laserschmelzen (SLM). Die Ergebnisse deuten darauf hin, dass die Scanstrategie einen vernachlässigbaren Einfluss auf die Phasenbildung und die Art des Gefüges hat, die während der SLM-Verarbeitung entsteht: Austenit ist die einzige Phase, die sich bildet, und alle Proben weisen eine zelluläre Morphologie auf. Die Scanstrategie beeinflusst jedoch erheblich die charakteristische Größe von Zellen und Körnern, die wiederum der Hauptfaktor für die Festigkeit unter Zugbelastung zu sein scheint. Andererseits haben Eigenspannungen offenbar keinen Einfluss auf die quasi-statischen mechanischen Eigenschaften der Proben. Das mit einem Streifenmuster mit Konturstrategie hergestellte Material weist das feinste Gefüge und die beste Kombination mechanischer Eigenschaften auf: Streckgrenze und Bruchdehnung liegen bei 550 MPa und 1010 MPa und die plastische Verformung bei über 50 %. Ein weiterer wichtiger Aspekt für die Anwendung des mittels SLM synthetisierten 316L-Stahls ist seine thermische Stabilität. Daher wurde der Einfluss des Glühens bei verschiedenen Temperaturen (573, 873, 1273, 1373 und 1673 K) auf die Stabilität der Phasen, der Zusammensetzung und des Gefüges des 316L-Edelstahls untersucht, der unter Verwendung des Streifenmuster mit Konturstrategie hergestellt wurde. Darüber hinaus wurden die durch die Wärmebehandlung induzierten Veränderungen genutzt, um die entsprechenden Variationen der mechanischen Eigenschaften der Proben unter Zugbelastung zu verstehen. Das Glühen hat keinen Einfluss auf die Phasenbildung: Bei allen hier untersuchten Proben wird ein einphasiger Austenit beobachtet. Darüber hinaus ändert das Glühen nicht die zufällige kristallographische Orientierung, die im Material nach der Synthese beobachtet wird. Das komplexe zelluläre Gefüge mit feinen Subkornstrukturen, die für die as-SLM-Proben im Ausgangszustand charakteristisch sind, ist bis zu 873 K stabil. Die Zellgröße nimmt mit steigender Glühtemperatur zu, bis das zelluläre Gefüge bei hohen Temperaturen nicht mehr beobachtet werden kann (T ≥ 1273 K). Die Festigkeit der Proben nimmt mit steigender Glühtemperatur durch die mikrostrukturelle Vergröberung ab. Die ausgezeichnete Kombination von Festigkeit und Duktilität des Materials im Ausgangszustand ist auf das komplexe zelluläre Gefüge und die Subkörner sowie die Fehlausrichtung zwischen Körnern, Zellen, Zellwänden und Subkörnern zurückzuführen. Mit dem Ziel, das mechanische Verhalten des 316L-Stahls weiter zu verbessern, wird der Einfluss harter Partikel einer zweiten Phase auf das Gefüge und die damit verbundenen mechanischen Eigenschaften untersucht. Dazu wurde mittels SLM ein Verbund aus einer 316L-Stahlmatrix und 5 Vol.% CeO2-Partikeln hergestellt. Die SLM-Parameter, die zu einer fehlerfreien 316L-Matrix führen, sind für die Herstellung von 316L/CeO2-Verbundproben nicht geeignet. Hochdichte Verbundproben können jedoch durch sorgfältige Einstellung der Laserscangeschwindigkeit unter Beibehaltung der anderen Parameter prozessiert werden. Die Zugabe der CeO2-Verstärkung verändert die Phasenbildung nicht, beeinflusst aber das Gefüge des Verbundwerkstoffs, welches im Vergleich zum partikelfreien 316L-Material deutlich verfeinert ist. Das verfeinerte Gefüge bewirkt eine signifikante Verstärkung im Verbund, ohne die plastische Verformung zu beeinträchtigen. Die Analyse des Einflusses einer zweiten Phase wird fortgesetzt, indem untersucht wird, wie TiB2-Partikel das Gefüge und die mechanischen Eigenschaften eines 316L-Edelstahls beeinflussen, der durch selektives Laserschmelzen hergestellt wird. Das für die unverstärkte 316L-Matrix charakteristische komplexe zelluläre Gefüge mit feinen Subkörnern ist in allen Proben zu finden. Die Zugabe der TiB2-Partikel reduziert die Größe der Körner und Zellen erheblich. Darüber hinaus sind die TiB2-Partikel in der 316L-Matrix homogen dispergiert und bilden kreisförmige Ausscheidungen mit einer Größe von etwa 50-100 nm entlang der Korngrenzen. Diese mikrostrukturellen Merkmale führen zu einer signifikanten Verfestigung im Vergleich zu den unverstärkten 316L-Proben. Diese Ergebnisse belegen, dass SLM erfolgreich zur Synthese von Verbundwerkstoffen aus dem Edelstahl 316L mit herausragenden mechanischen Eigenschaften im Vergleich zu einer unverstärkten 316L-Stahlmatrix eingesetzt werden kann. Dies könnte dazu beitragen, den Einsatz von SLM bei der Herstellung von Stahlmatrix-Verbundwerkstoffen für die Automobilindustrie, die Luft- und Raumfahrt und zahlreiche andere Anwendungen zu erweitern.
Among the different additive manufacturing processes, selective laser melting (SLM) represents an optimal choice for the fabrication of metallic components with complex geometries and superior properties. SLM parts are built layer-by-layer using high-energy laser beams, making SLM more flexible than conventional processing techniques, like casting. The fast heating/cooling rates occurring during SLM can result in remarkably different microstructures compared with conventional manufacturing processes. The high-temperature gradients characterising SLM can also have a positive effect on the microstructures and, in turn, on the mechanical properties of the SLM parts. Additionally, the SLM parts can be put into use with the necessity of minimal post-processing treatments. To date, a number of studies have been devoted to the parameters optimization or processing of composite materials with defect-free parts. The scanning strategy is one of the most influential parameters in materials processing by additive manufacturing. Optimization of the scanning strategy is thus of primary importance for the synthesis of materials with enhanced physical and mechanical properties. Accordingly, this thesis examines the effect of four different scanning strategies on the microstructure and mechanical behaviour of 316L stainless steel synthesized by selective laser melting (SLM). The results indicate that the scanning strategy has negligible influence on phase formation and the type of microstructure established during SLM processing: austenite is the only phase formed and all specimens display a cellular morphology. The scanning strategy, however, considerably affects the characteristic size of cells and grains that, in turn, appears to be the main factor determining the strength under tensile loading. On the other hand, residual stresses apparently have no influence on the quasi-static mechanical properties of the samples. The material fabricated using a stripe with contour strategy displays the finest microstructure and the best combination of mechanical properties: yield strength and ultimate tensile strength are about 550 and 1010 MPa and plastic deformation exceeds 50 %. Another important aspect for the application of 316L steel synthesized by SLM is its thermal stability. Therefore, the influence of annealing at different temperatures (573, 873, 1273, 1373 and 1673 K) on the stability of phases, composition and microstructure of 316L stainless steel fabricated by using the stripe with contour strategy has been investigated. Moreover, the changes induced by the heat treatment have been used to understand the corresponding variations of the mechanical properties of the specimens under tensile loading. Annealing has no effect on phase formation: a single-phase austenite is observed in all specimens investigated here. In addition, annealing does not change the random crystallographic orientation observed in the as-synthesized material. The complex cellular microstructure with fine subgrain structures characteristic of the as-SLM specimens is stable up to 873 K. The cell size increases with increasing annealing temperature until the cellular microstructure can no longer be observed at high temperatures (T ≥ 1273 K). The strength of the specimens decreases with increasing annealing temperature as a result of the microstructural coarsening. The excellent combination of strength and ductility exhibited by the as-synthesized material can be ascribed to the complex cellular microstructure and subgrains along with the misorientation between grains, cells, cell walls and subgrains. With the aim of further improving the mechanical behaviour of 316L steel, this works examines the effect of hard second-phase particles on microstructure and related mechanical properties. For this, a composite consisting of a 316L steel matrix and 5 vol.% CeO2 particles was fabricated by SLM. The SLM parameters leading to a defect-free 316L matrix are not suitable for the production of 316L/CeO2 composite specimens. However, highly-dense composite samples can be synthesized by carefully adjusting the laser scanning speed, while keeping the other parameters constant. The addition of the CeO2 reinforcement does not alter phase formation, but it affects the microstructure of the composite, which is significantly refined compared with the unreinforced 316L material. The refined microstructure induces significant strengthening in the composite without deteriorating the plastic deformation. The analysis of the effect of a second phase is continued by investigating how TiB2 particles influence the microstructure and mechanical properties of a 316L stainless steel synthesized by selective laser melting. The complex cellular microstructure with fine subgrains characteristic of the unreinforced 316L matrix is found in all samples. The addition of the TiB2 particles reduces significantly the sizes of the grains and cells. Furthermore, the TiB2 particles are homogeneously dispersed in the 316L matrix and they form circular precipitates with sizes around 50-100 nm along the grain boundaries. These microstructural features induce significant strengthening compared with the unreinforced 316L specimens. These findings prove that SLM can be successfully used to synthesize 316L stainless steel matrix composites with overall superior mechanical properties in comparison with the unreinforced 316L steel matrix. This might help to extend the use of SLM to fabricate steel matrix composites for automotive, aerospace and numerous other applications.

High-accuracy miniaturized components are increasingly in demand for various industries such as aerospace, biomedical, electronics, environmental, communication and automotive, and this coupled with new developments of High Speed Machining (HSM) has led to the emergence of a strong and viable technology in High Speed Micro Machining. This technology is very important in bridging the macro-domain and the nano- and micro- domains for making functional miniaturized components. High speed Micro Machining is a specific technology where high spindle speeds, high performances cutting tools and high accuracy control systems are used. The understanding of this technology is still not well established and theories are still under development. A major implication of the High Speed Micro Machining process is the relatively high machining forces with respect to the cutting tool's size, which often cause low process reliability and high costs, due to frequent tool failures and short tool life. The aim of this investigation is to contribute towards a fundamental understanding of the effects of increased spindle speed in High Speed Micro Machining.

The use of High Speed Milling (HSM) for the production of moulds and dies is becoming more widespread. Critical aspects of the technology include cutting tools, machinability data, cutter path generation and technology. Much published information exists on cutting tools and related data (cutting speeds, feed rates, depths of cut, etc.), however, relatively little information has been published on the evaluation of cutter paths for this application. Most of the research work is mainly focused on cutter path generation techniques. Works with regard to cutter path evaluation on tool wear and tool life, surface integrity and relevant workpiece machinability characteristics are scant. Therefore, a detailed knowledge on the evaluation of cutter path strategies and orientations when high speed rough and finish milling is essential in order to improve productivity and surface quality respectively. The present work deals with some aspects related to the evaluation on the machinabiltiy of hardened AISI H13 hot work tool steel of 52 Rockwell Hardness C scale when high speed rough and finish milling using designated cutter path strategies and orientations. A literature review has been carried out to identify the various geometrical forms that are commonly utilised and common cutter path strategies presently employed in the mould and die industries. A review on the cutter path strategies and techniques is identified and classified according to the rough or finish milling stage. The selection and evaluation techniques notably feed rate, cutting tools and cutter path strategies and orientations are presented. Machinability criteria in terms of tool life and tool wear, cutting forces, tool wear and vibration signatures, cutting temperature and chip formation are reviewed. Last but not the least, surface integrity analysis on machined hardened steels are detailed and reviewed. The experimental work was divided into three phases. The first phase dealt with the investigation by employing high axial depths of cut (10 mm < Ai <20 mm) on three main cutter path strategies when rough milling hardened steels. In the second phase, the spotlight of the research was on finish milling an inclined workpiece surface using different cutter path orientations through machinability assessments in order to identify the optimum cutter path orientation. In the final phase, the effect of various cutter path orientations on workpiece surface integrity when finish milling hardened steels was investigated. The experimental results for Phase 1 revealed that in general where higher material removal rates, shorter machining time, longer tool life and higher volume of metal removed were of concern, raster cutter path strategy was the most favourable at all axial depths of cut employed. In Phase 2 when finish milling at an inclined workpiece angle of 75 0, tool life was highest when employing a downward cutter path orientation. On the other hand, upward cutter path orientation would be preferred where low workpiece surface roughness was concerned. In the final phase, surface integrity analysis revealed that upward cutter path orientation in particular the single direction raster vertical upward orientation was the most preferred in achieving optimum component life.

Periodic surfaces structures with micrometer or submicrometer resolution produced on the surface of components can be used to improve their mechanical, biological or optical properties. In particular, these surfaces can control the tribological performance of parts, for instance in the automotive industry. In the recent years, substantial efforts have been made to develop new technologies capable to produce functionalized surfaces. One of these technologies is Direct Laser Interference Patterning (DLIP), which permits to combine high fabrication speed with high resolution even in the sub-micrometer range. In DLIP, a laser beam is split into two or more coherent beams which are guided to interfere on the work piece surface. This causes modulated laser intensities over the component’s surface, enabling the direct fabrication of a periodic pattern based on selective laser ablation or melting. Depending on the angle between the laser beams and the wavelength of the laser, the pattern’s spatial period can be perfectly controlled. In this study, we introduce new modular DLIP processing heads, developed at the Fraunhofer IWS and the Technische Universität Dresden for high speed surface laser patterning of polymers and metals. For the first time it is shown that effective patterning speeds of up to 0.90 m2/min and 0.36 m²/min are possible on polymer and metals, respectively. Line- and dot-like surface architectures with spatial periods between 7 μm and 22 μm are shown.

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.

No
This paper reports the results of an investigation into the selective laser sintering of a prealloyed high-speed steel powder. The structured development of processing conditions for single lines, single layers and multiple layers of material is reported, as are the flexural modulus and strength of the single- and multiple layer components. Infiltration with bronze was used to improve the mechanical properties of the components and it is concluded that selective laser sintering of high-speed steel allied to bronze infiltration can produce material with the mechanical properties to allow for use in load-bearing applications, but that further work is required to improve the density, mechanical properties and build rate if selective laser sintering is to develop as a general manufacturing process for hard metals.

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 .

碩士
正修科技大學
機電工程研究所
94
In this study, the cathodic arc plasma system with Ti and Cr target mate-rial is used to deposit CrN, TiN and TiCrN coating on the high-speed steel (SKH9) substrate under different vacuum values, and mechatronical recipro-cating friction tester with ball-on-block type is employed to investigate theeffects of different process parameters on the surface structure and mechani-cal properties of coating film. Moreover, the surface morphology and filmcomposition are observed by SEM and EDS. Experimental results are shown as follows: sample of C4 (wt.%: Ti 60.48, Cr 16.59, N 22.93) has the lowest surface roughness; sample of A4 (wt.%: Ti 33.14, Cr 30.96, N 35.90) have the highest film hardness and adhesionstrength; sample of A3 (wt.%: Ti 7.19, Cr 51.59, N 41.22) has the lowest friction co-efficient; samples of A3 (wt.%: Ti 7.19, Cr 51.59, N 41.22); and A4 (wt.%: Ti 33.14, Cr30.96, N 35.90) have the lowest wear rate.

博士
國立臺灣大學
材料科學與工程學研究所
94
The effect of tempering on the decomposition of retained austenite in a powder metallurgy (PM) high-speed steel, GPM A30, has been monitored with a high-speed dilatometer. The corresponding microstructures of specimens with different tempering cycles have been investigated by a combination of scanning electron microscopy and analytical transformation electron microscopy. The as-quenched structure of the steel studied is composed of retained austenite, untempered martensite and carbides. The results indicate that the complete transformation of retained austenite can be more nearly accomplished by two or triple tempering cycles than by a single long-time cycle. The possible transformation mechanism for the decomposition of retained austenite during multiple tempering cycles is attributed to the invariant-plane-strain of the prior martensitic transformation extending accommodation defects to the adjacent retained austenite, which favors further transformations in the subsequent tempering operations. There has been intensive research work on retained austenite and lath martensite in low-carbon alloy steels. However, little TEM research work has been carried out on twinned plate martensite with retained austenite in high-carbon alloy steels . It is naturally very difficult to produce electron-transparent samples for TEM (because the high-carbon alloys are quite brittle), but TEM investigation continues to assume greater significance in research. GPM A30 is a high-carbon grade in commercial P/M high speed steels, and is widely used in such applications as metal cutting tools and metal forming dies. In this work, dilatometric experiments were performed to investigate the tempering response in quench-treated specimens of GPM A30 high speed steel. The resulting scanning electron micrographs and transmission electron micrographs were examined to elucidate the microstructural evolution.