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1
Aziz, Khan Naveed. "RF Magnetron Sputtered AlCoCrCu0.5FeNi High Entropy Alloy (HEA) and High Entropy Ceramic (HEC) Thin Films." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/24615.
Full textAbstract:
High entropy-based materials in the form of thin films have been of growing interest recently for surface engineering applications due to their exceptional properties including high hardness, superior resistance to oxidation and corrosion, improved thermal stability, and high hydrophobicity. Sputter deposition of thin films comprised of several elements typically requires the use of targets containing multiple elements, making both the chemical composition and microstructure of the resulting films strongly dependent on the process parameters. Therefore, this thesis investigates the growth mechanism, composition variation and key physical properties of AlCoCrCu0.5FeNi high entropy alloy (HEA) and high entropy ceramic (HEC) thin films deposited by radio frequency (RF) magnetron sputtering using advanced characterization methods. The depositions were performed using a single stoichiometric AlCoCrCu0.5FeNi HEA target in non-reactive and reactive modes to explore various high entropy-based materials in the form of metallic HEA and ceramic HEC thin films.
This dissertation explores several key deposition parameters during the thin film growth for the AlCoCrCu0.5FeNi HEA system. The initial studies investigate the deposition of HEA thin films in non-reactive mode using argon only and explored the influence of working pressure and deposition power on the microstructure, composition and physical properties. Subsequent chapters report reactive sputtering deposition with various gas flow fractions (RN) using a combination of argon with nitrogen or argon with oxygen to fabricate ceramic thin films of high entropy nitride (HEN) and high entropy oxide (HEO), respectively. The overall findings elucidate that the modification of deposition conditions could be used to control and tune microstructures and chemical composition which regulate the physical properties of the AlCoCrCu0.5FeNi high entropy-based thin films having important implications for the development of surface protective coatings in the aerospace, energy and nuclear industries.
2
Löbel, Martin, Thomas Lindner, Thomas Mehner, and Thomas Lampke. "Microstructure and Wear Resistance of AlCoCrFeNiTi High-Entropy Alloy Coatings Produced by HVOF." Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-230210.
Full textAbstract:
The investigation of high-entropy alloys (HEAs) has revealed many promising properties. HEAs with a high share of Al and Ti are suitable for the formation of lightweight materials. Investigations of the alloy system AlCoCrFeNiTi showed high strength, hardness, ductility, and wear resistance, which makes this special alloy interesting for surface engineering and particularly for thermal spray technology. In this study, the suitability of inert gas-atomised HEA powder for high-velocity-oxygen-fuel (HVOF) thermal spray is investigated. This process allows for high particle velocities and comparatively low process temperatures, resulting in dense coatings with a low oxidation. The microstructure and phase composition of the atomised powder and the HVOF coating were investigated, as well as the wear behaviour under various conditions. A multiphase microstructure was revealed for the powder and coating, whereas a chemically ordered bcc phase occurred as the main phase. The thermal spray process resulted in a slightly changed lattice parameter of the main phase and an additional phase. In comparison with a hard chrome-plated sample, an increase in wear resistance was achieved. Furthermore, no brittle behaviour occurred under abrasive load in the scratch test. The investigation of wear tracks showed only minor cracking and spallation under maximum load.
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Belous, V. A., S. A. Firstov, V. F. Gorban, A. S. Kuprin, V. D. Ovcharenko, E. N. Reshetnyak, G. N. Tolmachova, and M. G. Kholomeev. "Properties of Coatings Deposited from Filtered Vacuum Arc Plasma with HEA Cathode." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35323.
Full textAbstract:
Ti-V-Zr-Nb-Hf metallic and nitride films were deposited by filtered vacuum arc plasma from a single
equiatomic HEA cathode. The composition, microstructure, mechanical properties, thermal stability and
corrosion properties were investigated.
The deposited metallic film has a two-phase structure with bcc and hcp-lattice. The nitride films were
found to have only an fcc structure. All coatings have nano-grained structures, with grain sizes 5 nm for
metallic and 36 nm for nitride. The nitride coatings have a compressive stress of around – 12,5 GPa, high
hardness ~ 40 GPa and elastic modulus ~ 450 GPa. After annealing in vacuum in range 400-1200 °C, 3 h
for every temperature, hardness decreased to 25 GPa. It was found that both the metallic and nitride coatings
exhibited their best corrosion resistance than steel samples in a 3,5 wt. % NaCl solution. The metallic
coatings showed better corrosion resistance than the nitride coatings.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35323
4
Sobol, O. V., A. A. Andreev, and V. Gorban. "Structural-Strained State and Mechanical Characteristics of Single-Phase Vacuum-Arc Coatings of Multicomponent High Entropy System Ti-V-Zr-Nb-Hf and Nitrides Based On It." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/34808.
Full textAbstract:
In this work was shown the high stability of the single-phase structural state of high entropy alloy of
Ti-V-Zr-Nb-Hf system in a vacuum-arc method of obtaining of coatings based on it. In the process of deposition
single-phase high entropy coatings with bcc-lattice which characterizes the cast state are formed in
vacuum, and upon obtaining in a nitrogen atmosphere single-phase nitride superhard coatings based
on fcc-metal lattice are formed. Such a stability of structure of multi-element alloy to high temperature
evaporation and deposition from high-energy plasma flows allows to use the techniques developed for
simple substitution phases in the analysis of their structural-stress state.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34808
5
Steneteg, Jakob. "Corrosion Resistant Multi-Component Coatings for Hydrogen Fuel Cells." Thesis, Linköpings universitet, Tunnfilmsfysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-174617.
Full textAbstract:
Multi-component coatings and high entropy alloys have in recent years attracted great interest for research, since they have shown to exhibit properties greater than the com- ponents of their parts. Today’s climate challenges requires transitioning from fossil fuels to renewable energy sources which demands use of new technology and new innovations. The hydrogen fuel cell is a technology which produces no carbon emissions, and the drive for innovation has led researchers to apply multi-component (high entropy alloys) coatings to invent the next generation hydrogen fuel cells and help the transition to renewable energy sources. This thesis has investigated the process-structure-property relationships of four deposi- tion growth parameters: target current (Itarget), argon pressure (PAr). substrate bias (Vsubstrate) and deposition time (tdeposition) on TiNbZrTa-coatings, grown by magnetron sputtering using an industrial deposition system. The range of the parameters have been: Itarget from 2.5 to 6 A, PAr from 1 to 17 mTorr, Vsubstrate from 30 to 200 V and tdeposition from 3.6 to 12 minutes (depending on Itarget). Coatings have been grown on Si (001) and stainless steel 304 and 316L substrates. The coating microstructure was analyzed by X-ray diffraction and electron microscopy. The results have yielded that all coatings are equimolar and that the coatings exhibit three different morphologies, two different topologies and two different corresponding structures. The different morphologies are wave, coarse columnar and fine columnar morphology. The two topologies are nodular and dune surface topology. The two different structures are a solid solution BCC (110) phase and an amorphous or nanocrystalline phase. The results indicate that parameters affecting the temperature of the substrate (Tsubstrate) is the prime decider for the final morphology of the coatings. High Itarget and Vsubstrate, low PAr and long tdeposition all increases Tsubstrate and results in a coating which exhibits a fine columnar morphology, dune topology and a solid solution BCC phase. These types of coatings have also proven to have improved corrosion resistance compared to the other type of coatings seen in this thesis. The other kind of coating is grown with low Itarget and Vsubstrate, high PAr and short tdeposition, which causes minimal increase of Tsubstrate. These growth parameters result in a coating with coarse columnar morphology, nodular topology and amorphous or nanocrystalline phase, with less corrosion resistance.FunMat II
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Тевосян, А. А. "Боридні покриття на основі високоентропійних сплавів." Master's thesis, Сумський державний університет, 2019. http://essuir.sumdu.edu.ua/handle/123456789/73025.
Full textAbstract:
Об’єкт дослідження – боридні покриття на основі високоентропійних сплавів та фізико-хімічні процеси, що обумовлюють формування та зміну фазового складу, структури і функціональних властивостей покриттів.
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Ляшко, В. О. "Карбідні покриття на основі високоентропійних сплавів." Master's thesis, Сумський державний університет, 2019. http://essuir.sumdu.edu.ua/handle/123456789/73026.
Full textAbstract:
В роботі досліджені карбідні покриття на основі високоентропійних сплавів та фізико-хімічні процеси, що обумовлюють формування та зміну фазового складу, структури і функціональних властивостей покриттів.
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Huser, Gautier. "Etude et sélection d’alliages à composition complexe sans cobalt à finalité tribologique." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST051.
Full textAbstract:
Il est nécessaire de développer des revêtements sans cobalt possédant une bonne résistance à l’usure afin de remplacer les alliages de type stellite® qui sont utilisés dans les centrales nucléaires. En effet, les débris de cet alliage sont activés sous flux neutronique et forme du 60Co, un isotope radioactif susceptible de contaminer le reste de l’installation. Les matériaux sans cobalt, base nickel ou base fer, proposés pour le moment ne présentent pas des propriétés tribologiques concurrentes à celles du stellite®. Les AHE (Alliage à Haute Entropie) et ACC (Alliage à Composition Complexe) peuvent être de bons candidats. En effet, ces alliages possèdent des domaines de compositions particulièrement étendus par rapport aux alliages conventionnels, qui donnent alors accès à un vaste espace de propriétés, en particulier mécaniques. Dans un premier temps, l’étude de plusieurs ACC par la méthode CALPHAD (CALculation of PHAse Diagram) a été réalisée afin de déterminer des compositions favorisant la présence de phases intermétalliques dures bénéfiques au comportement tribologiques. Le travail s’est poursuivi par la réalisation de plusieurs séries d’alliages. Des caractérisations microstructurales et tribologiques ont permis de retenir une unique composition comme meilleure candidate potentielle au remplacement des alliages base cobalt. Cette composition a alors été élaborée sous forme de poudre puis de revêtement en utilisant les procédés de DLD (Direct Laser Deposition) et compression isostatique à chaud. Leur microstructure et leur comportement tribologique a été comparé à celui du stellite®Currently, attempts are made to develop hardfacing cobalt-free alloys for coating the contact areas of moving parts of nuclear installations. In fact, under neutron flux, cobalt 59 is activated into cobalt 60, a highly radioactive isotope. Consequently, the coating debris generated by friction are likely to contaminate parts of the installation. Existing cobalt-free hardfacing alloys, nickel or iron bases, do not exhibit tribological properties competing with those of stellite®, a commonly used hardfacing cobalt base alloy. HEA (High Entropy Alloy) and CCA (Complex Concentration Alloy) may be good candidates. Indeed, compare to conventional alloys, they show vast composition domain giving access to a large range of properties. After an initial selection of elements, the phases of selected alloys were calculated by CALPHAD software (CALculation of PHAse Diagram). The compositions favoring the presence of hard intermetallic phases beneficial to tribological behavior were selected. Then several alloys were fabricated using different processes. From microstructural and tribological characterizations, one composition has been selected as the best potential cobalt-free hardfacing alloy candidate. Coatings of this composition were then fabricated by DLD (Direct Laser Deposition) and HIP (Hot Isostatic Pressing). Their microstructure and tribological behavior were measured and compared to those of stellite ®
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Сухонос, Я. В. "Мікроструктура та фізико-механічні властивості боридних багатокомпонентних покриттів." Master's thesis, Сумський державний університет, 2019. http://essuir.sumdu.edu.ua/handle/123456789/76755.
Full textAbstract:
В роботі представлено результати дослідження мікроструктури та фізико-механічних властивостей багатокомпонентних боридних покриттів на основі високоентропійних сплавів, які отримані різними методами осадження. Проаналізовані результати вивчення структурно-фазового стану і властивостей покриттів залежно від експериментальних умов і параметрів нанесення покриттів. Дослідження в роботі великої кількості покриттів ( залежно від тиску робочого газу та потенціалу зсуву підкладки) дозволило встановити закономірності формування структурного стану таких покриттів, виявити кореляцію між фазовим складом і фізико-механічними властивостями.
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Kushnerov, O. I. "MD simulation of AlCoCuFeNi high-entropy alloy nanoparticle." Thesis, Sumy State University, 2016. http://essuir.sumdu.edu.ua/handle/123456789/45791.
Full textAbstract:
High entropy alloys (HEA) are metallic compounds containing from 5 to 13 metallic elements in equiatomic ratios. In HEAs, because of the high mixing entropy, formation of brittle intermetallic phases is usually avoided and simple solid solutions are rather stabilized (BCC and/or FCC). This study used molecular dynamics (MD) package LAMMPS to simulate the AlCoCuFeNi nanoparticle (NP) crystallization.
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Погребняк, Олександр Дмитрович, Александр Дмитриевич Погребняк, Oleksandr Dmytrovych Pohrebniak, Артем Анатолійович Багдасарян, Артем Анатольевич Багдасарян, Artem Anatoliiovych Bahdasarian, Вадим Миколайович Борисюк, Вадим Николаевич Борисюк, Vadym Mykolaiovych Borysiuk, and J. Partyka. "Structure and Morphology of Nitride Coating (TiHfZrVNb)N After Thermal Annealing 600˚C." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35400.
Full textAbstract:
This study reports the influence of thermal annealing 600 °C on the characteristics of the (Ti-
HfZrVNb)N coatings prepared by vacuum arc melting at different deposition conditions. The crystal structures,
surface’s morphology were characterized by X-ray diffraction and atomic force microscopy. The results
indicate that nitride coatings based on high-entropy alloy TiHfZrVNb have fcc crystal structure. It is
shown that the nitride coatings (TiHfZrVNb)N have a good resistance to oxidation during thermal annealing
600 °C.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35400
12
Nordin, Norhuda Hidayah. "Phase transformation in High Entropy Bulk Metallic Glass (HE-BMG) and Lamellar Structured-High Entropy Alloy (HEA)." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21325/.
Full textAbstract:
An investigation into the phase transformation of metastable alloys such as high entropy alloys (HEAs) and high entropy bulk metallic glasses (HE-BMGs) was performed. Bulk metallic glasses (BMGs) and HEAs were known to have a metastable phase at high temperature, while HEAs was reported to have a sluggish diffusion at high temperature. Besides, the drawback of many single phase HEAs is that they are mechanically unstable due to the presence of single phase either body centred cubic (BCC) or face centred cubic (FCC) structures. Here, a systematic study on the crystal structure, physical and mechanical properties of TiZrHfNiCu HE-BMG and FeCoNi(BxAl1-x)0.1Si0.1 (0 ≤ x ≤ 1) lamellar structured HEA were explored. It was revealed that, a phase transformation occurred in HE-BMG in isothermal and non-isothermal conditions, yet the nucleation and growth behaviour was relatively slow at high temperature compared to most Zr-based amorphous alloys. This phenomenon was proven by the attained data of activation energy and crystallisation mechanism which reflect the crystallisation resistance of the alloy. The addition of boron as a substitution of aluminium in FeCoNi(BxAl1-x)0.1Si0.1 alloy changed the phase formation, phase stability, morphology characteristics and mechanical properties of the alloy. The unique lamellar herringbone-like structure was formed with increasing boron content and led to improvement of mechanical properties of the alloy such as the hardness from B0.4 to B1.0. Lamellar structured-HEA was designed to obtain a balance in strength and ductility for FeCoNi(Bx Al1-x)0.1Si0.1 HEA where it can be tailored by modifying the boron content. The optimum balance of strength (1550 MPa) and ductility (19%) was attained at 0.5 at% boron content.
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Löbel, Martin, Thomas Lindner, Robert Pippig, and Thomas Lampke. "High-Temperature Wear Behaviour of Spark Plasma Sintered AlCoCrFeNiTi0.5 High-Entropy Alloy." MDPI, 2019. https://monarch.qucosa.de/id/qucosa%3A34386.
Full textAbstract:
In this study, the wear behaviour of a powder metallurgically produced AlCoCrFeNiTi0.5 high-entropy alloy (HEAs) is investigated at elevated temperatures. Spark plasma sintering (SPS) of inert gas atomised feedstock enables the production of dense bulk material. The microstructure evolution and phase formation are analysed. The high cooling rate in the atomisation process results in spherical powder with a microstructure comprising two finely distributed body-centred cubic phases. An additional phase with a complex crystal structure precipitates during SPS processing, while no coarsening of microstructural features occurs. The wear resistance under reciprocating wear conditions increases at elevated temperatures due to the formation of a protective oxide layer under atmospherical conditions. Additionally, the coefficient of friction (COF) slightly decreases with increasing temperature. SPS processing is suitable for the production of HEA bulk material. An increase in the wear resistance at elevated temperature enables high temperature applications of the HEA system AlCoCrFeNiTi0.5.
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Ye, Jingrui. "Fabrication and Microscopic Characterization of AlCoCrCu0.5FeNi High Entropy Alloy Thin Films." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/25793.
Full textAbstract:
The high entropy alloy (HEA) was first discovered and reported in 2004. It was also called multi-principal element alloys (MPEAs). Generally, it is consisted of at least five elements in equimolar or near equimolar ratios, and the concentration of each element is varied in between 5% and 35%.
HEAs have many useful properties like thermal stability, excellent mechanical properties and high corrosion resistance which can all be applied in practice for various applications, such as high temperature, heat resistant coatings and diffusion barriers. They can also be used as the raw materials for soft magnetic films.
This thesis is focused on fabrication, microscopic structural characterization and property measurements of AlCoCrCu0.5FeNi high entropy alloy thin film fabricated at temperatures, from room temperature up to 350 oC by using Radio Frequency (RF) magnetron sputtering.
The RF magnetron sputtering experiments were conducted in the School of Physics at the University of Sydney. Surface energy tests, Scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Energy dispersive x-ray spectroscopy (EDS) were used to study the surface contact angles, the surface morphologies, the crystal structures, and the atomic concentrations of the high entropy alloy thin films.
In this study, FCC, BCC and the mixtures of both were found by using XPS and XRD. Thin films fabricated under higher temperatures was found to have the surface morphology with high roughness and large grain size by using SEM and EDS. With higher residual gases, the films presented with high density, hardness, and with higher Aluminum atomic concentration, the crystalline structures trended from FCC (111) to BCC (110). In conclusion, the mobility/energy of HEA atoms or ions, the Aluminum atomic concentration and the residual gases concentration, those three factors played important roles in fabricating different films. Thus, temperature was proved to be a key aspect in exploring new fabricating methods.
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Gwalani, Bharat. "Developing Precipitation Hardenable High Entropy Alloys." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1011755/.
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High entropy alloys (HEAs) is a concept wherein alloys are constructed with five or more elements mixed in equal proportions; these are also known as multi-principle elements (MPEs) or complex concentrated alloys (CCAs). This PhD thesis dissertation presents research conducted to develop precipitation-hardenable high entropy alloys using a much-studied fcc-based equi-atomic quaternary alloy (CoCrFeNi). Minor additions of aluminium make the alloy amenable for precipitating ordered intermetallic phases in an fcc matrix. Aluminum also affects grain growth kinetics and Hall-Petch hardenability.
The use of a combinatorial approach for assessing composition-microstructure-property relationships in high entropy alloys, or more broadly in complex concentrated alloys; using laser deposited compositionally graded AlxCrCuFeNi2 (0 < x < 1.5) complex concentrated alloys as a candidate system. The composition gradient has been achieved from CrCuFeNi2 to Al1.5CrCuFeNi2 over a length of ~25 mm, deposited using the laser engineered net shaping process from a blend of elemental powders. With increasing Al content, there was a gradual change from an fcc-based microstructure (including the ordered L12 phase) to a bcc-based microstructure (including the ordered B2 phase), accompanied with a progressive increase in microhardness. Based on this combinatorial assessment, two promising fcc-based precipitation strengthened systems have been identified; Al0.3CuCrFeNi2 and Al0.3CoCrFeNi, and both compositions were subsequently thermo-mechanically processed via conventional techniques. The phase stability and mechanical properties of these alloys have been investigated and will be presented. Additionally, the activation energy for grain growth as a function of Al content in these complex alloys has also been investigated.
Change in fcc grain growth kinetic was studied as a function of aluminum; the apparent activation energy for grain growth increases by about three times going from Al0.1CoCrFeNi (3% Al (at%)) to Al0.3CoCrFeNi. (7% Al (at%)). Furthermore, Al addition leads to the precipitation of highly refined ordered L12 (γ′) and B2 precipitates in Al0.3CoCrFeNi. A detailed investigation of precipitation of the ordered phases in Al0.3CoCrFeNi and their thermal stability is done using atom probe tomography (APT), transmission electron microscopy (TEM) and Synchrotron X-ray in situ and ex situ analyses.
The alloy strengthened via grain boundary strengthening following the Hall-Petch relationship offers a large increment of strength with small variation in grain size. Tensile strength of the Al0.3CoFeNi is increased by 50% on precipitation fine-scale γ′ precipitates. Furthermore, precipitation of bcc based ordered phase B2 in Al0.3CoCrFeNi can further strengthen the alloy. Fine-tuning the microstructure by thermo-mechanical treatments achieved a wide range of mechanical properties in the same alloy. The Al0.3CoCrFeNi HEA exhibited ultimate tensile strength (UTS) of ~250 MPa and ductility of ~65%; a UTS of ~1100 MPa and ductility of ~30%; and a UTS of 1850 MPa and a ductility of 5% after various thermo-mechanical treatments. Grain sizes, precipitates type and size scales manipulated in the alloy result in different strength ductility combinations. Henceforth, the alloy presents a fertile ground for development by grain boundary strengthening and precipitation strengthening, and offers very high activation energy of grain growth aptly suitable for high-temperature applications.
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Liu, Kaimiao. "Linking Enhanced Fatigue Life to Design by Modifying the Microstructure." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1538654/.
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Structural material fatigue is a leading cause of failure and has motivated fatigue-resistant design to eliminate risks to human lives. Intrinsic microstructural features alter fatigue deformation mechanisms so profoundly that, essentially, fatigue properties of structural materials become deviant. With this in mind, we initiated this project to investigate the microstructural effect on fatigue behavior of potential structural high entropy alloys. With a better understanding of the effect of microstructure features on fatigue properties, the ultimate goal was to engineer the microstructure to enhance the fatigue life of structural materials. The effects of two major deformation mechanisms presented here are twinning-induced fatigue crack retardation, and transformation-induced fatigue crack retardation. The fundamental principle of both mechanisms is to delay the fatigue crack propagation rate by altering the work hardening ability locally within the crack plastic zone. In ultrafine grained triplex Al0.3CoCrFeNi, nano-sized deformation twins were observed during cyclic loading in FCC matrix due to low stacking fault energy (SFE). The work-hardening ability of the material near the crack was sustained with the formation of twins according to Considere's criteria.
Further, due to the ultrafine-grained (UFG) nature of the material, fatigue runout stress was enhanced. In a coarse-grained, dual-phase high entropy alloy, persistent slip bands formed in FCC matrix during cyclic loading due mainly to the slight composition change that affects the SFE in the FCC matrix and eventually alters the deformation mechanism. Another way known to alter an alloy's work hardening (WH) ability is transformation-induced plasticity (TRIP). In some alloys, phase transformation happens due to strain localization, which alters the work-hardening ability.
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In a fine-grained, dual-phase metastable high entropy alloy, gamma (f.c.c.) to epsilon (h.c.p.) transformation occurred in the plastic zone that was induced from cracks. Thus, we designed a Cu-containing FeMnCoCrSi high entropy alloy that exhibited a normalized fatigue ratio of ~ 0.62 UTS (ultimate tensile strength). Our design approach was based on (a) engineering the gamma phase stability to attain sustained work hardening through delayed gamma (f.c.c.) to epsilon (h.c.p.) transformation to hinder fatigue crack propagation, (b) incorporating an ultrafine-grained microstructure to delay crack initiation, and (c) forming deformation twins to reduce the crack propagation rate. We verified that a UFG gamma dominant microstructure could provide opportunities for exceptional fatigue resistance, as sustained WH activity strengthened the material locally in the crack plastic zone, thereby validating our expectation that the combination of UFG and TRIP is a path to design the next generation of fatigue-resistant alloys.
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Löbel, Martin, Thomas Lindner, and Thomas Lampke. "Enhanced Wear Behaviour of Spark Plasma Sintered AlCoCrFeNiTi High-Entropy Alloy Composites." MDPI AG, 2018. https://monarch.qucosa.de/id/qucosa%3A32461.
Full textAbstract:
High hardness and good wear resistance have been revealed for the high-entropy alloy (HEA) system AlCoCrFeNiTi, confirming the potential for surface protection applications. Detailed studies to investigate the microstructure and phase formation have been carried out using different production routes. Powder metallurgical technologies allow for much higher flexibility in the customisation of materials compared to casting processes. Particularly, spark plasma sintering (SPS) enables the fast processing of the feedstock, the suppression of grain coarsening and the production of samples with a low porosity. Furthermore, solid lubricants can be incorporated for the improvement of wear resistance and the reduction of the coefficient of friction (COF). This study focuses on the production of AlCoCrFeNiTi composites comprising solid lubricants. Bulk materials with a MoS2 content of up to 15 wt % were produced. The wear resistance and COF were investigated in detail under sliding wear conditions in ball-on-disk tests at room temperature and elevated temperature. At least 10 wt % of MoS2 was required to improve the wear behaviour in both test conditions. Furthermore, the effects of the production route and the content of solid lubricant on microstructure formation and phase composition were investigated. Two major body-centred cubic (bcc) phases were detected in accordance with the feedstock. The formation of additional phases indicated the decomposition of MoS2.
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Hasan, Md Nazmul. "Microstructure and mechanical properties of a CrMnFeCoNi high-entropy alloy with gradient structures." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23036.
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High-entropy alloys (HEAs) that demonstrate excellent mechanical properties over steel-based alloys are not exempt from the common dilemma of strength–ductility trade-off, which limits their potential applications. One way to improve the property of CrMnFeCoNi HEA is by using the rotationally accelerated shot peening technique to introduce a gradient structure. Two gradient profiles—a thin gradient layer with an undeformed core and a fully deformed structure—are introduced by adjusting the processing parameters. The effects of these gradient profiles on mechanical properties and microstructural evolution at various loading conditions and temperatures are systematically explored. In this thesis, various mechanical tests are performed to investigate the effect of the gradient structure on mechanical properties such as tensile properties at room and cryogenic temperatures, compression at different strain rates and dynamic compression at high strain rates. Material characterisations are performed using various electron microscopic techniques to build a structure–property relationship and investigate microstructural evolution.
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Liu, Zhijie. "Application of a pulsed cathodic arc for deposition of high entropy alloy thin films." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/27518.
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High entropy alloys (HEAs) were highly valued because of their unique and desirable properties. A HEA is defined as having at least five elements in equimolar or near equimolar ratios, and the concentration of each element is between 5% and 35%. HEAs have many desired properties, such as excellent hardness, thermal stability, high electrical and oxidation resistance, and excellent mechanical properties. These advantages grant HEAs to overcome the conventional alloys and be applied in various fields like tools with excellent hardness, high temperature and durable characteristics, magnetic films, and diffusion barriers. While physical vapour deposition is one of the most common deposition technics in the thin film deposition application, cathodic arc deposition was chosen for the current study because of its remarkable advantages, such as high ionization rate and high deposition efficiency. Though cathodic arc has been used widely across industry applications, its application for high entropy alloy has been limited. Therefore, further research and experimentation are required to improve fabrication efficiency.
This thesis explores the plasma transportation associated with cathodic arc during HEA deposition. The high-speed framing camera examined the cathode spot motion as it is the primary plasma source. The deposition pattern and ion cross-section distribution experiment were conducted by deposition on the transparent plastic sheets under a range of operating parameters. The effectiveness of the electromagnetic coil was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM) for the thin film samples on the silicon wafers. Overall, this work shows the different outcomes for various cathode current and electromagnetic coil current inputs to optimise the deposition conditions further.
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Akbari, Azin. "COMBINATORIAL SCREENING APPROACH IN DEVELOPING NON-EQUIATOMIC HIGH ENTROPY ALLOYS." UKnowledge, 2018. https://uknowledge.uky.edu/cme_etds/87.
Full textAbstract:
High entropy alloys (HEA) are a relatively new group of alloys first introduced in 2004. They usually contain 5 to 6 different principle elements. Each of these elements comprise 5-35 at. % of the chemical composition of the alloy. There is a growing interest in the research community about the development of these alloys as well as their engineering applications. Some HEAs have interesting properties that have made them well suited for higher temperature applications, particularly refractory uses, while some have been shown to maintain their mechanical properties even at cryogenic temperatures.
Initially, the HEA research was focused on developing alloys with equiatomic compositions as it was believed that the single phase HEA would only form at such composition ratios. However, further research have found multiple HEAs with non-equiatomic chemical compositions. A major question that needs to be answered at this point is how to identify these non-equiatomic single phase alloy systems. Unlike the conventional alloys, the HEAs do not have a base element as a solvent, which complicates the identification of new alloy systems via conventional development techniques. To find a potential HEA, alloy development techniques of both exploratory and computational natures are being conducted within the community. Even though multiple HEAs have been successfully identified and fabricated by these techniques, in most cases they require extensive experimental data and are relatively time consuming and expensive. This study proposes a thin film combinatorial approach as a more efficient experimental method in developing new HEA alloy systems.
In order to study HEA systems with different crystal structures, nominal HEA compositions were selected, including: CoFeMnNiCu in order to achieve face centered cubic (FCC) HEA, OsRuWMoRe to obtain hexagonal closed packed (HCP) and VNbMoTaW in an attempt to form a body centered cubic (BCC) crystal structure. Thin film samples were fabricated by simultaneous magnetron sputtering of the elements onto silicon wafer substrates. The arrangement of the sputtering targets yielded a chemical composition gradient in the films which ultimately resulted in the formation of various phases. Some of these phases exhibited the desired single-phase HEA, albeit with non-equiatomic chemical compositions. Bulk samples of the identified HEA compositions were prepared by arc melting mixtures of the metals. Microstructure of both thin film samples and bulk samples were characterized via scanning electron microscopy (SEM), focused ion beam (FIB) and energy dispersive x-ray spectroscopy (EDX). The crystal structures of the samples were studied by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD) technique. Applying nano-indentation technique, the mechanical properties of some of the samples were screened over the composition gradient as well.
By applying this combinatorial thin film approach, single-phase FCC, HCP and BCC HEAs were detected and successfully produced in bulk form. Additionally, screening the properties of the compositionally gradient thin films, as well as their chemical composition and crystal structure, provided a thorough understanding of the phase space. This experimental approach proved to be more efficient in identifying new alloy systems than conventional exploratory development methods.
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Edris, Hossein. "Studies on high velocity oxy-fuel sprayed coatings of iconel 625 and Ni-Crâ†3Câ†2." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362891.
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Martin, Alexander Charles. "Initial Weldability of High Entropy Alloys for High Temperature Applications." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555496040477991.
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Jensen, Jacob K. "Characterization of a High Strength, Refractory High Entropy Alloy, AlMo0.5NbTa0.5TiZr." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492175560975813.
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Löbel, Martin, Thomas Lindner, Thomas Mehner, and Thomas Lampke. "Influence of Titanium on Microstructure, Phase Formation and Wear Behaviour of AlCoCrFeNiTix High-Entropy Alloy." Technische Universität Chemnitz, 2018. https://monarch.qucosa.de/id/qucosa%3A23475.
Full textAbstract:
The novel alloying concept of high-entropy alloys (HEAs) has been the focus of many recent investigations revealing an interesting combination of properties. Alloying with aluminium and titanium showed strong influence on microstructure and phase composition. However, detailed investigations on the influence of titanium are lacking. In this study, the influence of titanium in the alloy system AlCoCrFeNiTix was studied in a wide range (molar ratios x = 0.0; 0.2; 0.5; 0.8; 1.0; 1.5). Detailed studies investigating the microstructure, chemical composition, phase composition, solidification behaviour, and wear behaviour were carried out. Alloying with titanium showed strong influence on the resulting microstructure and lead to an increase of microstructural heterogeneity. Phase analyses revealed the formation of one body-centred cubic (bcc) phase for the alloy without titanium, whereas alloying with titanium caused the formation of two different bcc phases as main phases. Additional phases were detected for alloys with increased titanium content. For x ≥ 0.5, a minor phase with face-centred cubic (fcc) structure was formed. Further addition of titanium led to the formation of complex phases. Investigation of wear behaviour revealed a superior wear resistance of the alloy AlCoCrFeNiTi0.5 as compared to a bearing steel sample.
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Lindner, Thomas, Martin Löbel, Thomas Mehner, Dagmar Dietrich, and Thomas Lampke. "The Phase composition and microstructure of AlχCoCrFeNiTi alloys for the development of high-entropy alloy systems." Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-226527.
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Alloying aluminum offers the possibility of creating low-density high-entropy alloys (HEAs). Several studies that focus on the system AlCoCrFeNiTi differ in their phase determination. The effect of aluminum on the phase composition and microstructure of the compositionally complex alloy (CCA) system AlxCoCrFeNiTi was studied with variation in aluminum content (molar ratios x = 0.2, 0.8, and 1.5). The chemical composition and elemental segregation was measured for the different domains in the microstructure. The crystal structure was determined using X-ray diffraction (XRD) analysis. To identify the spatial distribution of the phases found with XRD, phase mapping with associated orientation distribution was performed using electron backscatter diffraction. This made it possible to correlate the chemical and structural conditions of the phases. The phase formation strongly depends on the aluminum content. Two different body-centered cubic (bcc) phases were found. Texture analysis proved the presence of a face-centered cubic (fcc) phase for all aluminum amounts. The hard η-(Ni, Co)3Ti phase in the x = 0.2 alloy was detected via metallographic investigation and confirmed via electron backscatter diffraction. Additionally, a centered cluster (cc) with the A12 structure type was detected in the x = 0.2 and 0.8 alloys. The correlation of structural and chemical properties as well as microstructure formation contribute to a better understanding of the alloying effects concerning the aluminum content in CCAs. Especially in the context of current developments in lightweight high-entropy alloys (HEAs), the presented results provide an approach to the development of new alloy systems.
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Hendrick, Michelle Renee. "The effects of combustion CVD-applied alumina coatings on the high temperature oxidation of a Ni-Cr alloy." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19635.
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RAJESHWAR, REDDY ELETI. "Deformation Mechanisms and Microstructure Evolution in HfNbTaTiZr High Entropy Alloy during Thermo-mechanical Processing at Elevated Temperatures." Doctoral thesis, Kyoto University, 2019. http://hdl.handle.net/2433/242505.
Full textAbstract:
京都大学0048
新制・課程博士
博士(工学)
甲第21767号
工博第4584号
新制||工||1714(附属図書館)
京都大学大学院工学研究科材料工学専攻
(主査)教授 辻 伸泰, 教授 乾 晴行, 教授 安田 秀幸
学位規則第4条第1項該当
Doctor of Philosophy (Engineering)
Kyoto University
DFAM
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Wang, Hao. "In-situ transmission electron microscopy investigation of deformation-induced microstructural evolution of a FeCoCrNiMn high-entropy alloy." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/20068.
Full textAbstract:
High-entropy alloys (HEAs) are alloys with multiple (usually ≥5) principal elements. HEAs are attracting increasing interest because of their promising mechanical properties and phase stability, which can be used for various applications, such as high-speed cutting tools, anticorrosive high-strength parts in chemical plants and deep-sea exploration due to the excellent mechanical properties at cryogenic temperatures. Thorough understanding of the structural evolution during deformation of HEAs is a prerequisite for understanding and further improving their superior mechanical properties, which is critical for future production of high-entropy alloys with desirable properties. Many HEAs form a stable single solid-solution phase. However, phase transformation could occur in some HEAs under certain circumstances, including high stress. Because stress concentration usually occurs at crack tips during deformation, it is interesting to check if any deformation-induced phase transformation would occur at crack tips during the deformation processes of HEAs. This thesis aims at using various transmission electron microscopy techniques to investigate the structural evolution of HEAs at room temperature. Research results showed surprisingly crystalline to amorphous phase transformation at crack tips in a FeCoCrNiMn HEA with an ultrafine-grained structure. Details of the phase transformation process was video recorded. The mechanism responsible for the phase transformation is discussed based on the observed microstructural evolution. Toughening introduced by nanobridging and the phase transformation is also briefly discussed.
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Anguo, Wang. "The effect of grain size on the low-cycle fatigue behaviours of a CrMnFeCoNi high entropy alloy." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/21129.
Full textAbstract:
High-entropy alloys (HEAs) alloys are alloys formed by at 5 or more elements, which have high strength, excellent ductility, and wear, corrosion and creep resistance. While the above-mentioned properties are very important and widely studied, fatigue properties are a more critical issue in most industrial applications. Fatigue causes over 90% of failure. Yet, the fatigue properties of HEAs have been less investigated. So, it worth to study the fatigue properties. It has been well-known that grain size plays a critical role in determining the mechanical properties of HEAs. However, the grain size effects on fatigue properties of HEAs has not been clear. This project aims to study the effect of grain size on the low-cycle fatigue (LCF) properties of a CrMnFeCoNi HEA. Results show that the fatigue life increased with decreasing grain size and/or decreasing strain amplitude. Fatigue-induced structural evolution of the HEA was complicated. Deformation of samples with fine and coarse grain sizes occurred mainly via planar slip at low strain levels, while wavy slip dominated the deformation of samples with the intermediate grain size. Planar slip was suppressed at a high strain regime. Dislocation cell structures, which are classic wavy slip microstructures, were commonly seen in intermediate grains at the high strain regime. The fatigue cracking behaviour at twin boundaries (TBs) in the HEA was also explored. Irrespective of grain size, the change from slip band cracking to TB cracking occurred with increasing the difference in the Schmid factors between matrix and twin. However, the required critical difference of Schmid factors for the transition of the dominant cracking mode decreases with decreasing grain size due to the reduced slip band spacing that increases the impingement sites on the TBs and facilitates the coalescence of defects and voids to initiate TBs cracks
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Ayyagari, Venkata A. "Surface Degradation Behavior of Bulk Metallic Glasses and High Entropy Alloys." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062863/.
Full textAbstract:
In this study, the surface degradation behavior was studied for typical examples from bulk metallic glasses (BMGs), metallic glass composites (MGCs) and high entropy alloys (HEAs) alloy systems that are of scientific and commercial interest. The corrosion and wear behavior of two Zr-based bulk metallic glasses, Zr41.2Cu12.5Ni10Ti13.8Be22.5 and Zr57Cu15.4Ni12.6Al10Nb5, were evaluated in as-cast and thermally relaxed states. Significant improvement in corrosion rate, wear behavior, and friction coefficient was seen for both the alloys after thermal relaxation. Fully amorphous structure was retained with thermal relaxation below the glass transition temperature. This improvement in surface properties was explained by annihilation of free volume, the atomic scale defects in amorphous metals resulting from kinetic freezing. Recently developed MGCs, with in situ crystalline ductile phase, demonstrate a combination of mechanical properties and fracture behavior unseen in known structural metals. The composites showed higher wear rates but lower coefficient of friction compared to monolithic amorphous glasses. No tribolayer formation was seen for the composites in sharp contrast to that of the monolithic metallic glasses. Corrosion was evaluated by open circuit potential (OCP) analysis and potentiodynamic polarization. Site-specific corrosion behavior was studied by scanning vibration electrode technique (SVET) to identify formation of galvanic couples. Scanning kelvin probe microscope was used to map elecropositivity difference between the phases and linked to wear/corrosion behavior. Phases with higher elecropositivity were more susceptible to surface degradation. Wear and corrosion synergy in marine environment was evaluated for two high entropy alloys (HEAs), CoCrFeMnNi and Al0.1CoCrFeNi. Between the two alloys, Al0.1CoCrFeNi showed better wear resistance compared to CoCrFeMnNi in dry and marine conditions due to quicker passivation, a higher magnitude of polarization resistance and significantly larger pitting resistance.
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Kushnerov, O. I., and V. F. Bashev. "Structure and mechanical properties of Al-Co-Cr-Fe-Mn-Ni-Si-V high-entropy films obtained by splat-quenching." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42650.
Full textAbstract:
The multicomponent films of Al-Co-Cr-Fe-Mn-Ni-Si-V high-entropy alloys obtained by splat-quenching from melt were investigated. Phase formation criteria for high-entropy alloys were considered. The films have a structure with body-centered cubic lattice. The value of lattice parameters of the investigated alloys suggests that the solid solutions are form on the base of Cr lattice, in view of its higher melting temperature.
The positive influence of microstrains level and dislocation density on the microhardness values of splat-quenched high-entropy alloys has been established. Improved mechanical characteristics are ensured by the strong distortion of the crystal lattice due to the differences in atomic radii of the elements.
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Kuprin, A. S., O. M. Morozov, V. A. Belous, S. A. Firstov, V. F. Gorban, V. D. Ovcharenko, E. N. Reshetnyak, G. N. Tolmachova, V. I. Zhurba, and V. O. Progolaieva. "Effects of Deuterium Implantation Dose on Hardness and Deuterium Desorption Temperature Range from High Entropy TiVZrNbHf and TiVZrNbHfN Coatings." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35363.
Full textAbstract:
High entropy TiVZrNbHf and TiVZrNbHfN coatings prepared by filtered vacuum arc plasma from a single
equiatomic HEA cathode. Similarly were obtained titanium and titanium nitride coatings. The structure
of coatings was investigated by X-ray analysis and the changes in nanohardness by nanoindentation method.
The effusion of the implanted deuterium was studied by thermal desorption spectroscopy (TDS).
It is shown that the structure of effusion spectrum is a function of deuterium dose. With increasing implantation
dose deuterium desorption temperature range from coatings is expanding in the direction of
lowering the temperature and the temperature of the peak maximum gas emission gradually shifts to lower
temperatures. For nitride coatings deuterium desorption starts at about room temperature and the maximum
rate of desorption at a temperature of ~500 K.
When irradiation doses more than 5×1017 D/cm2 hardness of nitride coatings decreased by half. Hardness
reduction of coatings is caused by occurrence hydride structural formations in coatings.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35363
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Huang, Ping-Kang, and 黃炳剛. "On High-Entropy Alloy and Nitride Coatings Sputtered from AlCrNbSiTiV Target." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/45557558479597094755.
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Lin, Shao-Yi, and 林少顗. "Nanomechanical Properties and Deformation Behavior of Multi-component High-entropy Alloy and Nitride Coatings." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/38066806767302667335.
Full textAbstract:
博士國立中興大學
材料科學與工程學系所
104
Our study could divide into three sections. First, we studied about (AlCrTaTiZr)Nx multi-component coatings. They were developed as protective hard coatings for tribological application. The mechanical properties, creep behaviors, deformation mechanisms and interface adhesion of the (AlCrTaTiZr)Nx coatings with different N contents were characterized. With increasing the N2-to-total flow ratio, RN, during sputtering deposition, the (AlCrTaTiZr)Nx coatings transformed from an amorphous metallic phase to a nanocomposite and finally a crystalline nitride structure. With increasing RN, the mechanical proerties was enhanced. The plastic deformation of the amorphous metallic coating proceeded through the formation and extension of shear bands, whereas dislocation activities dominated the deformation behavior of the crystalline nitride coatings. The secondary part of our stury was about (AlCrTaTiZr)NCy and (AlCrTaTiZr)NSiz multi-component coatings.It were developed by co-sputtering of alloy target and graphite/silicon in an Ar/N2 mixed atmosphere with the application of different substrate biases. All the coatings deposited in different conditions exhibited a simple face-centered cubic structure. With increasing substrate bias and graphite/silicon target power, the mechanical proerties was also enhanced, attributed to the densification of the coatings, the refinement of grains, the introduction of covalent-like carbide bonds, the formation of nanocomposite structure and the existence of large lattice distortions. Because of the severe distortions in the multi-component coatings caused by the addition of differently-sized atoms, the deformation mechanism was dominated by the activity of low-angle dislocations and/or stacking faults. In the deformed regions under indents, stacking faults or partial dislocations were formed, while in the stress-released regions, near-perfect lattices recovered. Final, we designed multi-component alloys whose nanomechanical properties and characterized their deformation behaviors. We control the lattice distortion and cohesive energy of all the multi-component alloys under the same level and observed the different mechanical properties of multi-element. The lattice volume increased with element number increased. Due to the expansion of lattice volume, there was deference between theoretical and experimental values, including elastic modulus and hardness. The quinary alloy showed a magnificent elastic recovery, revealing that the deformation mechanism of multi-componet materials (including nitrides) was dominated by partial dislocations or stacking faults.
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Alvi, Sajid. "Synthesis and Characterization of High Entropy Alloy and Coating." Licentiate thesis, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-73882.
Full textAbstract:
High entropy alloys (HEAs) are a new class of alloys that contains five or more principal elements in equiatomic or near-equiatomic proportional ratio. The configuration entropy in the HEAs tends to stabilize the solid solution formation, such as body-centered-cubic (BCC), face-centered-cubic (FCC) and/or hexagonal-closed-pack (HCP) solid solution. The high number of principal elements present in HEAs results in severe lattice distortion, which in return gives superior mechanical properties compared to the conventional alloys. HEAs are considered as a paradigm shift for the next generation high temperature alloys in extreme environments, such as aerospace, cutting tools, and bearings applications. The project is based on the development of refractory high entropy alloy and film. The first part of the project involves designing high entropy alloy of CuMoTaWV using spark plasma sintering (SPS) at 1400 oC. The sintered alloy showed the formation of a composite of BCC solid solution (HEA) and V rich zones with a microhardness of 600 HV and 900 HV, respectively. High temperature ball-on-disc tribological studies were carried out from room temperature (RT) to 600 oC against Si3N4 counter ball. Sliding wear characterization of the high entropy alloy composite showed increasing coefficient of friction (COF) of 0.45-0.67 from RT to 400 oC and then it decreased to 0.54 at 600 oC. The wear rates were found to be low at RT (4 × 10−3 mm3/Nm) and 400 oC (5 × 10−3 mm3/Nm) and slightly high at 200 oC (2.3 × 10−2 mm3/Nm) and 600 oC (4.5 × 10−2 mm3/Nm). The tribology tests showed adaptive behavior with lower wear rate and COF at 400 oC and 600 oC, respectively. The adaptive wear behavior at 400 oC was due to the formation of CuO that protected against wear, and at 600 oC, the V-rich zones converted to elongated magneli phases of V2O5 and helped in reducing the friction coefficient. The second part of the project consists of sintering of novel CuMoTaWV target material using SPS and depositing CuMoTaWV refractory high entropy films (RHEF) using DC-magnetron sputtering on silicon and 304 stainless steel substrate. The deposited films showed the formation of nanocrystalline BCC solid solution. The X-ray diffraction (XRD) studies showed a strong (110) preferred orientation with a lattice constant and grain size of 3.18 Å and 18 nm, respectively. The lattice parameter were found to be in good agreement with the one from the DFT optimized SQS (3.16 Å). The nanoindentation hardness measurement at 3 mN load revealed an average hardness of 19 ± 2.3 GPa and an average Young’s modulus of 259.3 ± 19.2 GPa. The Rutherford backscattered (RBS) measurement showed a gradient composition in the cross-section of the film with W, Ta and Mo rich at the surface, while V and Cu were found to be rich at the substrate-film interface. AFM measurements showed an average surface roughness (Sa) of 3 nm. Nano-pillars of 440 nm diameter from CuMoTaWV RHEFs were prepared by ion-milling in a focused-ion-beam (FIB) instrument, followed by its compression. The compressional yield strength and Young’s modulus was calculated to be 10.7 ± 0.8 GPa and 196 ± 10 GPa, respectively. Room temperature ball-on-disc tribological test on the CuMoTaWV RHEF, after annealing at 300 oC, against E52100 alloy steel (Grade 25, 700-880 HV) showed a steady state COF of 0.25 and a low average wear rate of 6.4 x 10-6 mm3/Nm.
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陳家裕. "Development of multicomponent high-entropy alloys for thermal spray coating." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/47099338451611909570.
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Huang, Ping-Kang, and 黃炳剛. "Research of multi-component high -entropy alloys for thermalspray coating." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/32057932770890578348.
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Luo, Jin-Tai, and 羅錦泰. "Development of oxidation-resistant coating for refractory high-entropy alloys." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/jcef2n.
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Lu, Che-Wei, and 呂哲維. "Electrochemical properties of CoCrFeMnNi high entropy alloy- a comparison with Fe5Mn3CoCr medium entropy alloy." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/6z56du.
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碩士國立臺灣大學
材料科學與工程學研究所
106
In recent years, Fe5Mn3CoCr medium entropy alloy (MEA) has been reported as an alloy system which shows transformation-induced plasticity effect during deformation. The excellent strength and ductility combination of this alloy is even better than CoCrFeMnNi high entropy alloy (HEA), but the corrosion behavior is still unknown. In this study, the corrosion behavior of CoCrFeMnNi HEA and Fe5Mn3CoCr MEA were investigated. The environments chose for the cyclic polarization measurement were 3.5wt% NaCl solution with different pH values (pH=3, 6, 9, 12) and temperatures (10oC, 40oC, 70oC) and 0.1M H2SO4 solution. The results show that, compared with CoCrFeMnNi HEA, Fe5Mn3CoCr MEA the had smaller passivation region in every test environment, but the two substrate had almost the same corrosion current density value in 3.5wt% NaCl solution without any adjustment. In 0.1M H2SO4 solution, the corrosion current density of Fe5Mn3CoCr MEA is higher than CoCrFeMnNi HEA. The surface morphologies of CoCrFeMnNi HEA after polarization measurement in 3.5wt% NaCl solution exhibited a pitting appearance, which was resulted from the disintegration of inclusions on surface; Fe5Mn3CoCr MEA showed “lath-shaped” corrosion morphologies which were caused by the connection of pits. After cyclic polarization in 0.1M H2SO4 solution, CoCrFeMnNi HEA showed intergranular corrosion and galvanic corrosion morphologies; Fe5Mn3CoCr MEA showed “branch-like” corrosion morphologies which is attributed to the dissolution of ε martensite.
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Kao, Yih-Farn, and 高逸帆. "High-entropy alloy mediated growth of graphene." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/55042565088569128165.
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博士國立清華大學
材料科學工程學系
102
Pyrolysis of acetylene over thin films made of CuxFeCoNiMn yields graphene and sheet dimension is found to control by x. Monolayer structure forms at x = 0.5 and sheet size reaches a value as large as 600 m2. Layer number increases as x rises and turbostratic graphite forms at x = 1.5. The x-controlled growth mechanism involves five consecutive steps and each is supported by experimental data.
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Tsao, Te Kang, and 曹德綱. "Alloy Design Cast High Entropy Superalloys for High Temperature Applications." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/7277mt.
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博士國立清華大學
材料科學工程學系
105
In this study, high entropy alloys have been developed toward high temperature applications. According to the most widely used high temperature material superalloys, the microstructure of face-centered cubic (FCC) γ matrix with uniformly distributed L12 γ′ precipitates implies the more balanced high temperature strength and ductility. So, the thermal stability and strength of highly alloyed Ni3Al were studied initially. The strengthening effect on developing a γ′ composition toward higher entropy is significant, due to higher anti-phase boundary energy of the order phase. However, the order-disorder transition temperature would be decreased with the more random atomic distribution in γ′ lattice. The microstructure stability of the γ - γ′ alloys with medium to high mixing entropy were then studied. It was found that the high temperature alloys cannot be solely designed by entropy term, but should also enhance the ordering enthalpy of γ′ phase, to avoid lowering the thermal stability of γ′ phase. Through alloy designs, we have also found that present alloys are quite different from the conventional Ni-, Co- or Fe-based alloy design, but is within a range of stable (Ni, Co, Fe)-rich system. This composition space has rarely been studied through the development of superalloys. In addition, such highly-soluted (Ni-Co-Fe) matrix can exhibit an enlarged solubility of alloying contents, while remains good phase stability till high temperatures. Therefore, they have been named as high entropy superalloys (HESA). Since grain boundaries might be drawbacks to the thermal properties, HESAs have been successfully casted into the directionally-solidified (DS) structure by Bridgeman method. In terms of the high temperature mechanical properties, HESAs can exhibit comparable high temperature hardness, tensile strength and creep resistance to that of commercial superalloys due to the stable γ - γ′ microstructure, high volume fraction of γ′ precipitates, high anti-phase boundary energy for γ′ strengthening and low stacking fault energy to hinder dislocation climb. Good surface stability of HESA in high temperature oxidizing and corrosive environments were also demonstrated, which can be attributed to the rapid formation of continuous Chromia or Alumina for surface protection. Furthermore, with less alloying of refractory elements, HESAs exhibit the apparent advantages in lower density and cost of materials. Nevertheless, there are still concerns such as the directional coarsening of γ′ for HESAs cannot contribute to the creep resistance, and the strength of γ matrix is still lower than that of superalloys. As a result, further rooms for composition optimization of HESA exist. To summary, the novel high entropy superalloys are with unique composition, good thermal properties and improved cost-performance, thus can be promising as a new type of high temperature alloy.
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Huang, Wen-Wei, and 黃文威. "Effect of Al0.5CoCrFeNi2 high entropy alloy particle on strength of AZ91 alloy." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/48e979.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
107
In this study, 10 wt. % of Al0.5CoCrFeNi2 high entropy powder with the size of 10 μm and 90 μm were added to AZ91 alloy by powder metallurgy. According to the result of hardness and compression strength, particle size of 10 μm was the best candidate. Magnesium-based composites were then fabricated with four different addition amount (5 wt. %, 10 wt. %, 15 wt. %, 30 wt. %) to study the effect. The analysis was then carried out using SEM, XRD, MTS dynamic testing and Vickers hardness. The experimental results showed that the phase composition of magnesium-based composites with different addition amounts are composed of α-Mg, Mg17Al12, Al-Mn precipitates and Al0.5CoCrFeNi2. The microscopic results show that the high entropy powder did not change the phase structure within the composite during the powder metallurgy process. In the compression test results, addition of 5wt. % 10 μm will increase the maximum compressive strength and yield strength from 45.73MPa to 150.45Mpa and 42.5MPa to 149.9Mpa, respectively. The hardness test showed that the hardness of the composite with high entropy powder were enhanced. The hardness of adding 10 μm is enhanced from 55.4 HV to 139.3 HV, while the addition of 90 μm result the lower hardness of 108.6HV.
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Chen, Yi-Hung, and 陳翊閎. "Structural Transition in High Entropy Alloy CoCrFeMnNi Subjected to High Pressure." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/s3mbgv.
Full textAbstract:
碩士國立交通大學
材料科學與工程學系所
105
An equal-molar CoCrFeMnNi high-entropy alloy has the cubic crystal system of face-centered-cubic (FCC) at room temperature and atmospheric pressure. The recent research believed that the high-entropy has the property of low stacking fault energy, and excellent mechanic property because of the structure of nanocrystalline in low temperature. However, there was no phase-changing observed. This research used Angular-dispersive X-ray Diffraction (ADXRD) under high-pressure, pressurized the CoCrFeMnNi high-entropy alloy system to 20GPa. After analyzing diffraction data, there was phase transformation from FCC to Hexagonal Close Packing (HCP) when the pressure reached 7.1GPa. Both phases existed until the maximum pressure of 20GPa. When the pressure was unloaded to atmospheric pressure, there are remaining HCP-phase in the alloy, which shows the phase transformation is a non-reversible phenomenon. Besides observing phase transformation under high-pressure and the remaining HCP phase, this research will also calculate the lattice constant, ratio and full width at half maximum (FWHM) of both phases. Then, the result of the analysis will be compared with other theses, and to ensure that high-entropy alloy will not be affected by hydrostatic pressure in a high-pressure environment and non-isotropic compression. During the transformation of the material, there was corresponding texture and slip system. After comparison with other thesis, we discovered that when the phase of that alloy was transformed to HCP, the texture distribution is similar with Zine under pressurized. And confirmed the final phase of the alloy should be a uniform single phase. Finally, this research will investigate the phase transformation mechanism under high-pressure environment.
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Yang, Chien-chang, and 楊健章. "Environments Corrosion Behavior of FeCoNiCrAl0.5 Bulky High Entropy Alloy." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/16631098985979736826.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
97
The corrosion behavior of FeCoNiCrAl0.5 bulky high entropy alloy was studied. The homogenization treatment of the as-cast alloy specimen was processed. After water quenching serial heat-treatment processes were carried out. The corrosion properties, mechanical properties and microstructures of the specimens had been evaluated after the immersion tests with the NaCl, NaOH and H2SO4 solutions, respectively. The alloy has higher corrosion rate in 3.5 wt% NaCl aqueous solutions due to significant segregation of Cr-riched phase. Because of the active sensitivity zone of appreciable potential difference the alloy was preferentially attacked along the Cr-riched phase. The alloy exhibits excellent hardness after the immersion tests in NaOH and H2SO4 solution.
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Lin, Szu Yen, and 林思延. "Electrochemical Corrosion Properties of the High Entropy Alloy ( Al5Cr12Fe35Mn28Ni20 )." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/73102611505623444288.
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碩士中國文化大學
材料科學與奈米科技研究所
99
This research aims to explore the corrosion behavior and electrochemical properties of the high entropy alloy (HEA) AlCrFeMnNi ，to see whether increasing the amount of cold work (0% ，30% and 60%) would increase the pitting corrosion resistance ，and to achieve the critical pitting temperature (CPT) of the alloy in a specific aqueous environment containing chloride (Cl-) or fluoride (F-) through increasing the bath temperature (20-90℃). Experiments were conducted separately in sulfuric acid sodium chloride，ammonium chloride and sodium fluoride solutions and the result showed that under the room temperature the type 304 stainless steel showing a better pitting corrosion resistance than the HEA ；judging from the anodic polarization curves and SEM observations ，higher degree of cold work of the HEA has a better pitting corrosion resistance. Exposing AlCrFeMnNi alloy in acidic or in chloride environment showed that the component Al would easily react with the solution and be damaged by pitting corrosion leaving large amount of pits on the surface of the specimen . In dealing with such HEA it is possible to enhance the surface passivity for corrosion protection by means of increasing the degree of cold work .It is also observed that the CPT of this particular alloy increases with the increasing concentration of the fluoride solution and the highest CPT was achieved for the HEA with the highest degree of cold work. Keyword：high entropy alloy、critical pitting temperature
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Peng, Bo-Sen, and 彭柏森. "Alloy design and mechanical properties study of titanium-rich light-weight high-entropy alloy." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/x6z675.
Full textAbstract:
碩士國立中央大學
材料科學與工程研究所
107
High-entropy alloys (HEA) attract great attention in past few decades. Most HEA researches mainly concentrate on the heavier multi-principal elements with equiatomic or near-equiatomic alloys. In this study, we focus on the light-weight and non-equiatomic medium-entropy alloys (MEA) system with low density (below 5g/cm3). Series of non-equiatomic quaternary alloy system, Ti-Al-Cr-Nb、Ti-Al-Cr-V were firstly designed by using calculating parameter (∆S、∆H、δr), then further modified into quinary Ti-Al-Cr-Nb-V alloy system. All samples were prepared by vacuum arc melting and rapidly cooling process. The XRD results of Ti-Al-Cr-Nb 、Ti-Al-Cr-V and Ti-Al-Cr-Nb-V MEA reveal the single BCC structure. The hardness value of Ti60-Al-Cr-Nb reduced from 480Hv to 365Hv with decreasing the Al content which implies that the ratio of Ti/ Al elements plays an important role on the alloy hardness. The optimum mechanical performance occurs at Ti60-Al-Cr-Nb-V MEA with tensile yield strength of 1009 MPa, fracture strength of 1223 MPa, and plastic strain of 27.1%. In summary. the Ti60-Al-Cr-Nb-V MEA not only possesses higher mechanical properties than the commercial Ti6Al4V alloy, but also has similar density, wear resistance, and oxidation behavior to commercial Ti alloys. Therefore, it is believed that the Ti60-Al-Cr-Nb-V MEA can be a promising light-weight structure material for the applications of transportation vehicles and sport equipment.
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Chen, Hong-Siang, and 陳泓翔. "Microstructure and characterisation of high entropy alloy (TiVCrZrNbMoHfTaWAlSi) Nitride film." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/qzq779.
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碩士國立勤益科技大學
機械工程系
105
In this study, a high-entropy alloy nitride film was prepared by a DC sputtering machine. A nitride film was deposited on a silicon wafer and quartz glass (SiO2) without applying a substrate bias. The working pressure was 4x10-3 Torr and the sputtering was fixed at 300W The temperature and temperature of the substrate were fixed at 300 ° C, and the film composition and microstructure were controlled by adjusting the nitrogen and argon flow rate (RN) in the vacuum. The film thickness was 1000 nm ± 50 nm, , Scanning electron microscopy, visible spectrophotometer, Hall effect analyzer, chemical analysis electron spectrometer, atomic force microscope, nano indentation tester and wear tester (Rub Tester) and other instruments were analyzed and compared to explore the different nitrogen flow On the microstructure, chemical composition, electrical properties, optical and mechanical properties of the film. Component analysis, the high entropy alloy due to the composition of a variety of elements, the majority of its composition is uneven distribution, which is due to high entropy effect caused. It is known that the microstructure of the film is amorphous phase structure at the beginning of the observation. When the flow rate of nitrogen and argon is more than 15%, the microstructure is transformed into the crystalline phase. When the RN is 15%, it belongs to the FCC structure, and its preferred direction is (200) , When the RN increases to 20%, the crystallinity of the film increases, because the film nitrogen content increases, contributing to the formation of nitride phase, in addition to the preferred direction into (111), when RN to 49%, (200) peak appears For the final preferred direction, which is due to sputtering atoms kinetic energy is too high, may lead to recrystallization effect, but too high kinetic energy will damage the film structure, to produce re-nucleation effect, reduce grain size. And RN = 49% when the surface aggregates have been reduced much, and the grain size also decreased, mainly the atomic kinetic energy decreased, the film compressive stress decreased. In the mechanical properties, it was found that when the RN = 49%, the hardness of the film was the highest, and the hardness was 34 GPa. The Young's modulus was 276 GPa. The film will rise with the rise of the resistivity of the RN, which may be due to N increase → the number of electrons → lead to increased resistivity caused. The optimum friction coefficient of this nitride film was found to be about 0.5 ± 0.08, and the friction coefficient was related to the ratio of nitrogen to argon, grain and hardness. Finally, in the cutting, compared with the general naked knife, this high entropy nitride film also has a better hardness and cutting properties.
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Fang, Shuang, and 方雙. "Microstructures and Mechanical Properties of CoCrFeMnNiVx High Entropy Alloy Films." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/hbe4ev.
Full textAbstract:
碩士國立臺灣大學
材料科學與工程學研究所
107
In the present work, CoCrFeMnNiVx (x = 0, 0.07, 0.3, 0.7, 1.1) high entropy alloy films were fabricated by magnetron co-sputtering. For low contents of V, typical face-centered cubic (fcc) peaks were identified in X-ray diffraction patterns. With the increasing V content, the diffraction peaks became broadening and the formation of amorphous phase was promoted. TEM observations showed abundant nanotwins in films with low V contents and the transition from fcc to amorphous structure with the increasing V content. The 3D APT reconstruction results revealed no precipitate in the as-deposited films (x = 0, 0.07). Mechanical properties of the films were studied using nanoindentation and micro-pillar compression tests. The films exhibited high hardness ranging from 6.8 to 8.7 GPa. The serrated flow associated with shear banding showed in the stress-strain curves for films with x ≥ 0.3. When x = 0.07, excellent yield strength of ~3.8 GPa and ultimate compressive strength of ~4.9 GPa were achieved with little sacrifice in ductility. The presence of nanotwins contributed to the strain hardening effect.
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Tsai, Chih-Fang, and 蔡致芳. "High-Entropy Alloy Nanoparticles as Electrocatalysts for Direct Methanol Fuel Cells." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/50943003627171622233.
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碩士國立交通大學
材料科學與工程系所
95
In this study, fabrication and electrochemical characterization of high-entropy electrocatalyst on noncatalyzed gas diffusion electrode by RF sputter deposition was reported. XRD analysis of the as-deposited film exhibited a crystalline FCC phase while EDS confirmed its composition as Pt52Fe10Co9Ni9Cu12Ag8. SEM images revealed nanoparticles nodules growing on the carbon particles. Cyclic voltammetry (CV) was used to analyze its performance as anode electrocatalyst for direct methanol fuel cell. The area under CV curve was proportional to the amount of electrocatalyst deposited. However, in specific activity sample with 5 nm electrocatalyst demonstrated the highest values, 400~600 mA/cm2•mg. Our work presents invaluable information on electrochemical performance of high-entropy electrocatalyst. High-entropy nanoparticles of PtxFe(100-x)/5Co(100-x)/5Ni(100-x)/5Cu(100-x)/5Ag(100-x)/5 (x = 22, 29, 52, 56) were then prepared by sputter deposition on pretreated carbon cloth. XRD patterns indicated crystalline FCC phases and SEM images revealed nanoparticulate nodules grown on surface of carbon particles with their average sizes increasing with deposition time. Cyclic voltammetry demonstrated enhancements of catalytic performance with increasing Pt amount. However, in specific activity Pt52Fe11Co10Ni11Cu10Ag8 exhibited the highest capability, reaching values as high as 504 and 462 mA/cm2•mg. This work provides invaluable information in unique electrocatalyst design using high-entropy concept. Comparison of the properties of six-component alloys and binary alloys Pt-M (M= Fe, Co, Ni, Cu, Ag) were studied in last part. All the phases of binary alloys were fcc as identified by XRD. In addition, the morphologies of PtFe, PtCo, and PtCu were similar in their nodules structure to that of Pt52Fe10Co9Ni9Cu12Ag8. In contrast, PtAg formed a large particle on carbon black. The PtCu showed the highest catalytic activity, and PtAg was the poorest because of its large of particles size and weak strength of M-O bonding. The six-component alloy exhibited characteristics between each binary alloys, imply the mixing effects of the multi-components.
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Chen, Huang-Jen, and 陳皇仁. "A study of phase transformations in an Al0.5CoCrFeNi2 high entropy alloy." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/13260718801691617600.
Full textAbstract:
碩士國立臺灣科技大學
材料科技研究所
93
We have studied the microstructures of the constituent phases of a Al0.5CoCrFeNi2 multi-component alloy in two conditions which one was in the as-cast condition and the other wais in hot forged, cold rolled, annealed at 1050℃, then heat treatment at lower temperatures. For the alloy in the as-cast condition, the dendrites appeared in the OM observation, and only FCC peaks were observed from the XRD analysis; however, L12 phase was the major phase confirmed by the TEM study. The L12 phase was the derivative phase from the FCC parent phase. The mechanism for the phase transformation was FCC → L12 during the solidification process. For the alloy in the as-quenched condition, the major phase of the alloy is FCC. The minor B2 phase precipitated from the FCC matrix and had the K-S orientation relationship with the FCC matrix: [10 ]FCC // [11 ]B2，(111) FCC // (101) B2. For the alloy in the annealing conditions at 1000, 900, and 850℃, the microstructure of the alloy is similar to that in the as-quenched condition. However, for the annealing temperature below 800℃ we found the matrix phase had changed from FCC to L12 phase. Therefore the upper limit temperature for the existence of the B2 phase is between 800 and 850℃. For the annealing temperature at 700 and 600℃, we found a new FCC phase with high Al content precipitated from the L12 matrix. The lattice constant of the new FCC phase is a = 0.6785 nm which is higher than that of pure Al and different from those of Al2O3. For the annealing temperatures at 600 and 500℃, we found another new coherent FCC phase precipitated from the L12 matrix. The lattice constant of the new FCC phase is three times larger than that of L12 phase. The mechanism of the phase transformation of the new coherent FCC phase is FCC→L12→new coherent FCC phase. Both new FCC phases have never been observed in the multi-component alloy systems.