Ziel der Arbeit ist es, die Eignung pulvermetallurgischer Verfahren für die spätere industrielle Nutzung, die Werkstoffeigenschaften sowie das Sinterverhalten für High-Entropy Alloys (HEAs) zu evaluieren. Aufgrund des einphasigen Gefüges ist CoCrFeMnNi eine geeignete Modelllegierung, um die grundlegenden Eigenschaften von HEAs zu analysieren und wird im Rahmen dieser Dissertation exemplarisch für die High-Entropy Alloys verwendet. Verdüstes CoCrFeMnNi-Pulver wird mit drucklosem Sintern und Spark Plasma Sintern unter Verwendung von geeigneten Prozessparametern kompaktiert. Ausgewählte mechanische und physikalische Eigenschaften von CoCrFeMnNi werden bestimmt und im Vergleich mit konventionellen Legierungen bewertet. Die festigkeitssteigernden Mechanismen Kornfeinung und Ausscheidungshärtung werden diskutiert. Durch die Zugabe von Titan zu dem inertgasverdüsten HEA-Pulver wird dafür eine aushärtbare Legierung hergestellt. Zum besseren Verständnis der beim Sintern in HEAs ablaufenden Diffusionsvorgänge wird ein Modell zum Ausheilen isolierter Poren anhand eines vereinfachten Systems für einen binären Mischkristall entwickelt und diskutiert. Des Weiteren wird die Aktivierungsenergie beim Sintern anhand von Schwindungsversuchen berechnet und anschließend mit konventionellen Legierungen verglichen.

No description available.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23157号 / 工博第4801号 / 新制||工||1751(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

<p>Ni-based superalloys continue to exert themselves as the industry standards in high stress and highly corrosive/oxidizing environments, such as are present in a gas turbine engine, due to their excellent high temperature strengths, thermal and microstructural stabilities, and oxidation and creep resistances. Gas turbine engines are essential components for energy generation and propulsion in the modern age. However, Ni-based superalloys are reaching their limits in the operating conditions of these engines due to their melting onset temperatures, which is approximately 1300 °C. Therefore, a new class of materials must be formulated to surpass the capabilities Ni-based superalloys, as increasing the operating temperature leads to increased efficiency and reductions in fuel consumption and greenhouse gas emissions. One of the proposed classes of materials is termed refractory complex concentrated alloys, or RCCAs, which consist of 4 or more refractory elements (in this study, selected from: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) in equimolar or near-equimolar proportions. So far, there have been highly promising results with these alloys, including far higher melting points than Ni-based superalloys and outstanding high-temperature strengths in non-oxidizing environments. However, improvements in room temperature ductility and high-temperature oxidation resistance are still needed for RCCAs. Also, given the millions of possible alloy compositions spanning various combinations and concentrations of refractory elements, more efficient methods than just serial experimental trials are needed for identifying RCCAs with desired properties. A coupled computational and experimental approach for exploring a wide range of alloy systems and compositions is crucial for accelerating the discovery of RCCAs that may be capable of replacing Ni-based superalloys. </p> <p>In this thesis, the CALPHAD method was utilized to generate basic thermodynamic properties of approximately 67,000 Al-bearing RCCAs. The alloys were then down-selected on the basis of certain criteria, including solidus temperature, volume percent BCC phase, and aluminum activity. Machine learning models with physics-based descriptors were used to select several BCC-based alloys for fabrication and characterization, and an active learning loop was employed to aid in rapid alloy discovery for high hardness and strength. This method resulted in rapid identification of 15 BCC-based, four component, Al-bearing RCCAs exhibiting room-temperature Vickers hardness from 1% to 35% above previously reported alloys. This work exemplifies the advantages of utilizing Integrated Computational Materials Engineering- and Materials Genome Initiative-driven approaches for the discovery and design of new materials with attractive properties.</p> <p> </p> <p><br></p>

The main aim of this thesis was to design and develop new Aluminium based compositionally complex alloys (CCAs) using the high entropy alloy (HEA) concept, and to understand their evolution of microstructures during casting and also after the secondary process which is heat-treatment, and finally to evaluate their subsequent mechanical properties. Prior to the development of alloys, a computational technique ThermoCalc was used which helped in understanding the phase formation in various results. Use of thermodynamic physical parameters for predicting the stability of single-phase fields was done to assess their validity in predicting the compositional regions of the alloys developed. The first alloy developed is Al73.6Mg18Ni1.5Ti1.9Zr1Zn4 in at% (NiTiZrZn) CCA. The microstructure consists of the FCC as a primary phase with ~49% volume fraction along with β-AlMg and intermetallic (IM) phases including Al3Ni, Al3Ti, and Al3Zr. After casting, the microstructure showed some presence of eutectic structures. The Al3Ti, and Al3Zr IM phases seemed to precipitate early which led to less homogenization of Ti and Zr, causing deviation in the amount of these elements in the matrix. Further, the CCA was heat-treated at 375 oC for 24hrs and 48hrs and the evolution of microstructure along with its hardness and phase transformation characterisation was investigated. The second developed alloy was quaternary Al65.65Mg21.39Ag10.02Ni2.94 in at% (AgNi) CCA. In the as-cast state, the main phase (matrix) was FCC with ~64 % volume fraction along with BCC, β-AlMg and Al3Ni IM phases. There was a good level homogenization of all elements in the alloy. They were further heat- treated at 400 oC for 24 hrs and 48 hrs and were studied for any change in microstructure along with its hardness and thermal stability. This CCA had the highest hardness value from all developed CCAs. Lastly, in order to check how Ni affects the microstructure and properties of (AgNi) CCA, a ternary Al67.2Mg22.09Ag10.7 in at% (Ag) CCA was developed. The composition was kept such that it is exactly 97% by excluding the Ni. During the development of this alloy, the cast was cooled in two ways first being the normal cooled just like other CCAs and second being a fast cooling method. Both of these alloys consists of the FCC phase as a primary phase with 72% volume fraction along with BCC and β-AlMg. Both of them were also heat treated at 400 oC for 24 hrs and 48 hrs to evaluate any changes in microstructure and also to assess its hardness and thermal stability.

O desenvolvimento de novos materiais com baixa densidade e propriedades mecânicas estáveis em altas temperaturas é necessário para reduzir o consumo de combustível e consequentemente a emissão de gases no setor aeroespacial. Uma nova classe de materiais chamada HEAs (Ligas de Alta Entropia), que combinam elementos refratários e alumínio podem ser candidatas para superar esse desafio. Ligas de Alta Entropia contendo Al-Zr-Nb-Ti-V estão sendo estudadas em nosso grupo de pesquisa. Os diagramas de fases são uma ferramenta necessária para o desenvolvimento e otimização dessas ligas. O objetivo do presente trabalho é a investigação experimental do sistema ternário Al-V-Zr a 1200°C. Ligas do sistema foram fundidas em um forno a arco com cadinho de cobre refrigerado a água e eletrodo não consumível de tungstênio sob atmosfera de argônio. Pedaços das amostras foram embrulhados em folhas de Zr e tratadas a 1200°C por 10 dias usando tubos de sílica em vácuo primário para alcançar o equilíbrio termodinâmico. Para a observação das microestruturas, as amostras foram preparadas pelo método metalográfico padrão. A composição e microestrutura das amostras foram analisadas por microscopia eletrônica de varredura (MEV) e espectroscopia por energia dispersiva (EDS). A caracterização microestrutural das amostras foi complementada por difratometria de raios X (DRX) utilizando pó e radiação de Cu-K?. No trabalho publicado por Guzei (1993) foi proposto a existência de duas fases ternárias com estequiometria Zr0,9V0,4Al2,7 e Zr13V2Al5. Entretanto neste trabalho, apenas a fase ternária Zr0,9V0,4Al2,7 foi observada. Em contrapartida, observou-se a estabilidade uma outra fase ternária com estequiometria aproximada (Zr,Al)2V e protótipo Ti2Ni. Uma nova seção isotérmica a 1200°C foi proposta baseada no equilíbrio termodinâmico determinado pelas medições das composições das fases. / The development of new materials with low density and stable mechanical properties at high temperature is necessary to reduce fuel consumption and consequently the emission of gases. A new class of material called HEA combining refractory elements and aluminum can be good candidate to overcome this challenge. High entropy alloys in the Al-Zr-Nb-Ti-V system are being investigated in our research group. The phase diagram data are a necessary tool for the design and optimization of the alloys. The objective of these study is an experimental research of the Al-V-Zr ternary system at 1200°C. Several alloys were melted in an arc furnace using non-consumable tungsten electrode in a water cooled copper crucible, under an inert atmosphere of argonium. Parts of the samples were treated at 1200 °C for 10 days using silica tubes sealed under primary vacuum in order to achieve the thermodynamic equilibrium. For the observation of microstructures, the specimens were prepared following conventional metallographic methods. The compositions and microstructures of the alloys were investigated by scanning electron microscopy (SEM) and electronic microanalysis (EDS). The microstructural characterization was complemented by X-ray diffractrometry (XRD) on powder using Cu-k? radiation. In the work published by Guzei (1993) the existence of two ternary phases with the stoichiometry Zr0,9V0,4Al2,7 and Zr13V2Al5 is indicated. However, in this work only the ternary phase Zr0,9V0,4Al2,7 was observed. In addition, another ternary phase with approximate stoichiometry (Zr,Al)2V and prototype Ti2Ni was observed. A new isothermal section at 1200°C is proposed based on the thermodynamic equilibria determined to measured compositions of the phases.

O desenvolvimento de novos materiais com baixa densidade e propriedades mecânicas estáveis em altas temperaturas é necessário para reduzir o consumo de combustível e consequentemente a emissão de gases no setor aeroespacial. Uma nova classe de materiais chamada HEAs (Ligas de Alta Entropia), que combinam elementos refratários e alumínio podem ser candidatas para superar esse desafio. Ligas de Alta Entropia contendo Al-Zr-Nb-Ti-V estão sendo estudadas em nosso grupo de pesquisa. Os diagramas de fases são uma ferramenta necessária para o desenvolvimento e otimização dessas ligas. O objetivo do presente trabalho é a investigação experimental do sistema ternário Al-V-Zr a 1200°C. Ligas do sistema foram fundidas em um forno a arco com cadinho de cobre refrigerado a água e eletrodo não consumível de tungstênio sob atmosfera de argônio. Pedaços das amostras foram embrulhados em folhas de Zr e tratadas a 1200°C por 10 dias usando tubos de sílica em vácuo primário para alcançar o equilíbrio termodinâmico. Para a observação das microestruturas, as amostras foram preparadas pelo método metalográfico padrão. A composição e microestrutura das amostras foram analisadas por microscopia eletrônica de varredura (MEV) e espectroscopia por energia dispersiva (EDS). A caracterização microestrutural das amostras foi complementada por difratometria de raios X (DRX) utilizando pó e radiação de Cu-K?. No trabalho publicado por Guzei (1993) foi proposto a existência de duas fases ternárias com estequiometria Zr0,9V0,4Al2,7 e Zr13V2Al5. Entretanto neste trabalho, apenas a fase ternária Zr0,9V0,4Al2,7 foi observada. Em contrapartida, observou-se a estabilidade uma outra fase ternária com estequiometria aproximada (Zr,Al)2V e protótipo Ti2Ni. Uma nova seção isotérmica a 1200°C foi proposta baseada no equilíbrio termodinâmico determinado pelas medições das composições das fases. / The development of new materials with low density and stable mechanical properties at high temperature is necessary to reduce fuel consumption and consequently the emission of gases. A new class of material called HEA combining refractory elements and aluminum can be good candidate to overcome this challenge. High entropy alloys in the Al-Zr-Nb-Ti-V system are being investigated in our research group. The phase diagram data are a necessary tool for the design and optimization of the alloys. The objective of these study is an experimental research of the Al-V-Zr ternary system at 1200°C. Several alloys were melted in an arc furnace using non-consumable tungsten electrode in a water cooled copper crucible, under an inert atmosphere of argonium. Parts of the samples were treated at 1200 °C for 10 days using silica tubes sealed under primary vacuum in order to achieve the thermodynamic equilibrium. For the observation of microstructures, the specimens were prepared following conventional metallographic methods. The compositions and microstructures of the alloys were investigated by scanning electron microscopy (SEM) and electronic microanalysis (EDS). The microstructural characterization was complemented by X-ray diffractrometry (XRD) on powder using Cu-k? radiation. In the work published by Guzei (1993) the existence of two ternary phases with the stoichiometry Zr0,9V0,4Al2,7 and Zr13V2Al5 is indicated. However, in this work only the ternary phase Zr0,9V0,4Al2,7 was observed. In addition, another ternary phase with approximate stoichiometry (Zr,Al)2V and prototype Ti2Ni was observed. A new isothermal section at 1200°C is proposed based on the thermodynamic equilibria determined to measured compositions of the phases.

No description available.

Master‘s thesis deals with the preparation and evaluation single-phase high-entropy alloy based on cobalt, chromium, iron, nickel and manganese and its variants strengthened by dispersion of oxidic particles. High-entropy alloy was prepared in powder form by mechanical alloying from the equiatomic proportions of atomic powders. Obtained powder was subsequently compacted by spark plasma sintering. By the method of mechanical alloying were successfully prepared single-phase high-entropy alloy and its variant strengthened by dispersion of nanometric yttria oxides. It has been found that the oxide particles present in the microstructure of high-entropy alloy significantly block mobility of grain boundary and dislocation at elevated temperatures. As a result of this behavior were observed doubling of alloy strength and decreasing of creep rate at 800 °C.

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