Article
Materials Science, Multidisciplinary
Z. Q. Zhang, S. Ketov, S. Fellner, H. P. Sheng, C. Mitterer, K. K. Song, C. Gammer, J. Eckert
Summary: Diffusion plays a significant role in phase formation and transformation in solid-state alloys. In a high-entropy alloy (HEA), the influence of element diffusion on phase formation and transition behavior was systematically studied. The thermodynamic effect governs the evolution of major phases, while the diffusion direction is controlled by the Gibbs free energy gradient. The sluggish diffusion effect is not dominant during reactive diffusion.
MATERIALS & DESIGN
(2022)
Article
Materials Science, Multidisciplinary
J. Charkhchian, A. Zarei-Hanzaki, A. Moshiri, H. R. Abedi, Jiajia Shen, J. P. Oliveira, Kanwal Chadha, Clodualdo Aranas
Summary: This study investigates the short-time thermal phase-stability of the as-cast eutectic AlCoCrFeNi2.1 high entropy alloy. Microstructural characterization, thermodynamic calculations, and assessment of mechanical properties were conducted to explore the effect of different temperatures and soaking times on the stability of primary dendritic regions and the formation of ordered phases. The results show that the primary dendritic regions grow and destabilize with an increase in annealing temperature and soaking time, leading to the formation of needle shape B-2 ordered phases. Despite the unstable nature of the primary constituent phases, the material hardness increases significantly at a moderate soaking time.
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T
(2022)
Article
Chemistry, Multidisciplinary
Rui Feng, Bojun Feng, Michael C. Gao, Chuan Zhang, Joerg C. Neuefeind, Jonathan D. Poplawsky, Yang Ren, Ke An, Michael Widom, Peter K. Liaw
Summary: High-entropy alloys show promising applications at high temperatures and a single-phase alloy with high-temperature strength can be designed based on intrinsic material characteristics. The high-temperature strength retention is attributed to mechanisms such as large atomic-size and elastic-modulus mismatches, insensitive temperature dependence of elastic constants, and dominance of non-screw character dislocations caused by strong solute pinning.
ADVANCED MATERIALS
(2021)
Article
Materials Science, Multidisciplinary
Haofei Sun, Meifeng Li, Hao Zhang, Jing Liu
Summary: The oxidation behavior of FeCrNi medium entropy alloy was investigated through experimental observations and density functional theory (DFT) calculations. The study found that at 900 degrees C, the alloy forms a desirable and continuous oxide layer, while at 1000 degrees C, the oxide layer becomes discontinuous with penetration of oxide. These observations highlight the significant role of phase structure in promoting the formation of protective oxide scales and influencing oxidation resistance.
Article
Chemistry, Physical
P. F. Li, Y. J. Ma, H. Ma, S. W. Ta, Z. Yang, X. T. Han, M. J. Kai, J. H. Chen, Z. H. Cao
Summary: In this study, single-layered and multilayered amorphous high entropy alloys were prepared to investigate their diffusion barrier performance. It was found that the multilayered structure exhibited better barrier performance due to the absence of grain boundary diffusion path and severe lattice distortion in the amorphous structure.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Article
Nanoscience & Nanotechnology
N. N. Liang, R. R. Xu, G. Z. Wu, X. Z. Gao, Y. H. Zhao
Summary: A nanocrystalline high-entropy alloy was produced by high pressure torsion, and the evolution of microhardness and microstructure during subsequent isochronal annealing was studied. The alloy exhibited nano-grains and deformation nano twin lamella, which contributed to its hardness. Annealing below 600°C induced hardening without precipitation effect, while annealing above 600°C resulted in evident recrystallization and grain growth. The high thermal stability of the alloy was attributed to kinetic sluggish diffusion effect and deformation twin boundaries.
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
(2022)
Article
Materials Science, Multidisciplinary
Piyush Kumar, M. R. Rahul, Sumanta Samal, Abhijit Ghosh, Gandham Phanikumar
Summary: The microstructure and texture evolution of a high-entropy alloy with chemical composition Fe11.5Co20.6Ni40.7Cr12.2Al7.8Ti7.2 (at. pct) during high-temperature deformation was investigated. The alloy showed significant flow softening at low temperatures due to cracking, while high-temperature softening was attributed to dynamic recrystallization. The study also analyzed the flow stress and deformation mechanism, and characterized the microstructure and texture of the deformed sample.
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
(2023)
Article
Chemistry, Physical
Kaiwei Zhang, Feng He, Zhongsheng Yang, Dingcong Cui, Junjie Li, Zenan Yang, Jincheng Wang, Zhijun Wang
Summary: The study found that Re and Ru have certain effects on the stability and coarsening kinetics of the L1(2) phase in the Ni29Co27Fe27Cr3Al7Ti7 high entropy alloy. Both Re and Ru can promote the formation of L2(1) precipitates, and they reduce the coarsening rate of the L1(2) phase by slowing down atomic diffusion.
JOURNAL OF ALLOYS AND COMPOUNDS
(2021)
Article
Chemistry, Physical
Mohammadreza Mokhtare, Milad Zohrevand, Amir Momeni, Saeed Sadeghpour, Mahesh Somani
Summary: The influence of Re addition on the thermal stability of the AlMo0.5NbTa0.5TiZr refractory high-entropy alloy was investigated. The addition of Re significantly improved the phase stability of the alloy under aging conditions, attributing to the decelerated atomic diffusion. The segregation of Zr and the formation of large needle-like HCP precipitates in the microstructure were effectively restricted by the addition of Re, resulting in the appearance of only spherical fine precipitates.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Materials Science, Multidisciplinary
Abhishek Mehta, Yongho Sohn
Summary: Experimental measurements of chemical and tracer diffusion coefficients in Al0.25CoCrFeNi high-entropy alloy suggest that diffusion may not necessarily be sluggish, indicating a more complex diffusion behavior in high-entropy alloys than previously thought.
MATERIALS RESEARCH LETTERS
(2021)
Article
Chemistry, Physical
Zhong Zheng, Hong Zhao, Lixian Sun, Marcela M. Bilek, Zongwen Liu
Summary: The thermal stability of dual-phase AlCrFeCoNiCu0.5 high entropy alloy thin films at high temperatures (up to 600 degrees C, under vacuum) was studied. The microstructure and chemical composition evolution were analyzed using X-ray diffraction, transmission Kikuchi diffraction, and transmission electron microscopy. The mechanical properties were determined by nanoindentation. The results showed that the FCC phase fraction increased with annealing temperature, and the morphology and size of the grains varied with temperature. The mechanical properties of the films also improved with annealing temperature. These findings provide important insights into the microstructure and property changes of dual-phase HEA thin films at high temperatures.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Materials Science, Multidisciplinary
Jia Liu, Shubin Wang, Junfeng Wang, Peiying Shi, Jiayu Cui, Da Shu, Zhibo Du, Weichao Wang, Donghong Wang, Baode Sun
Summary: This work assesses the laser beam weldability of an equiatomic TiZrHfNbTa refractory high entropy alloy (HEA) and the dissimilar weldability of TiZrHfNbTa to C103 niobium-based alloy. The single BCC phase remains stable in both the TiZrHfNbTa welding joint and HEA-C103 dissimilar welding joint. Fine equiaxed grains are obtained in both weld fusion zones with no detectable cracks. Despite the presence of some porosity in the fusion zone, the tensile properties of the welded samples are comparable to the base materials. This study confirms the excellent laser weldability of the prototype TiZrHfNbTa refractory HEA and its good dissimilar weldability to the commonly used C103 alloy.
INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
Sheetal Kumar Dewangan, Ornov Maulik, Devesh Kumar, Saurav Kumar, Vinod Kumar, Byungmin Ahn
Summary: In this study, the impact of heat treatments on AlFeCuCrMgx alloys prepared by mechanical alloying and spark plasma sintering was investigated. The phase evolution and microstructure changes of these alloys at different temperatures were studied using XRD, SEM, and TEM techniques.
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T
(2023)
Article
Chemistry, Physical
Zahra Zarei, Milad Zohrevand, Amir Momeni, Saeed Sadeghpour, Mahesh Somani
Summary: This paper investigates the effect of heat treatment process on the microstructure evolution and hardness variation of a cast and homogenized AlMo0.5NbTa0.5TiZr refractory high-entropy alloy (RHEA). The study reveals that phase decomposition occurs in a shorter time than reported previously, with Zr and Ti separation identified as the main cause. The decomposition leads to the formation of Zr-rich needle-like phase constituents and Ti-rich globular ones. The presence of these phases results in a transformation of crystal structure from body-centered cubic (BCC) to hexagonal close-packed (HCP). The increase in annealing temperature and/or time further enhances the proportion of HCP phase, and the hardness of the alloy increases significantly.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Materials Science, Multidisciplinary
Jianren Zhou, Mark Kirk, Pete Baldo, Shengmin Guo, Fengyuan Lu
Summary: The HfNbTaTiVZr refractory high entropy alloy fabricated by arc melting exhibits single-phase body centered cubic structure. Radiation-induced amorphization is observed at 2 displacements per atom at 298 K, with the specimen maintaining its crystal structure at 423 K. The large atomic size mismatch in the studied RHEA facilitates the amorphization process, challenging the current understanding of phase stability of RHEAs upon irradiation.
Article
Materials Science, Ceramics
Stephan Stich, Kuan Ding, Qaisar Khushi Muhammad, Lukas Porz, Christian Minnert, Wolfgang Rheinheimer, Karsten Durst, Juergen Roedel, Till Froemling, Xufei Fang
Summary: Experimental modulation of dislocation-based plasticity in single-crystal SrTiO3 by increasing oxygen vacancy concentration impacts dislocation nucleation and motion. This is evidenced by nanoindentation and bulk compression tests on a nano-/microscale level.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2022)
Article
Materials Science, Multidisciplinary
Kuan Ding, Enrico Bruder, Christian Dietz, Karsten Durst, Xufei Fang
Summary: The study demonstrates that high-pressure torsion processing improves the oxidation resistance and mechanical properties of FeCr alloy with ultrafine-grained microstructure. Thin and dense oxide scales formed on top of the samples after oxidation, providing excellent protection for the metallic substrate. Nanoindentation study reveals dislocation nucleation, crack formation, and oxide scale penetration events during indentation.
Article
Materials Science, Multidisciplinary
Christian Minnert, Karsten Durst
Summary: Different loading protocols have been developed to investigate the creep properties of materials using instrumented indentation testing technique, with a recent focus on a new indentation creep method maintaining constant contact pressure. This study compares results from constant contact pressure creep tests with uniaxial and constant load hold indentation creep experiments, revealing similar stress exponents between constant contact pressure and uniaxial tests. Additionally, a significant change in the power law exponent at large stress reductions was observed in both uniaxial and constant contact pressure tests, indicating a shift in deformation mechanism of ultrafine grained metals.
JOURNAL OF MATERIALS RESEARCH
(2022)
Article
Materials Science, Multidisciplinary
Timo Fromm, Sebastian Bruns, Marie-Christin Mueller, Alexander Fink, Rudolf Borchardt, Stefan M. Rosiwal, Karsten Durst
Summary: A novel process was developed for fabricating diamond-metal laminates, with the successful creation of diamond-based biomimetic brick-and-mortar structures. The laminates exhibit high nominal strengths exceeding other ceramic-metal composites by at least a factor of two, with fracture energy in a medium range. Diamond layers provide damage tolerance in the laminates.
MATERIALS & DESIGN
(2022)
Article
Multidisciplinary Sciences
Julia Auernhammer, Markus Langhans, Jan-Lukas Schaefer, Tom Keil, Tobias Meckel, Markus Biesalski, Robert W. Stark
Summary: Researchers used an atomic force microscopy-based method to investigate the local stiffness of fibers as a function of indentation depth. They found that the walls in the fiber structure provide protection against mechanical loading and established a spatially resolved mechanical map of the fiber. Additionally, they compared their results with imaging from fluorescence confocal laser scanning microscopy by labeling the fibers with fluorescent proteins.
SN APPLIED SCIENCES
(2022)
Article
Materials Science, Multidisciplinary
M. Takhsha Ghahfarokhi, F. Casoli, C. Minnert, S. Bruns, E. Bruder, R. Cabassi, K. Durst, O. Gutfleisch, F. Albertini
Summary: Nanoindentation was applied to study the effect of localized plastic deformation on the martensitic transformation of epitaxial Ni-Mn-Ga films on a MgO substrate. The cooling and heating curves for the nanoindented areas were analyzed, showing a thermodynamically governed local increase of the martensitic transformation temperature as a function of applied loads. The observed effect is local and disappears beyond a certain distance from the pile-ups around the residual impressions.
Article
Chemistry, Multidisciplinary
Sebastian Bruns, Christian Minnert, Laszlo Pethoe, Johann Michler, Karsten Durst
Summary: The increasing use of oxide glasses in high-tech applications demonstrates the demand for novel engineering techniques on nano- and microscale. Shaping operations of oxide glasses at room temperature usually require high temperatures close or beyond the point of glass transition T-g. However, electron irradiation has been found to facilitate the viscous flow of amorphous silica at room temperature, offering potential for local microengineering.
Article
Materials Science, Multidisciplinary
Franziska Staab, Enrico Bruder, Lukas Scha, Konstantin Skokov, David Koch, Benjamin Zingsem, Esmaeil Adabifiroozjaei, Leopoldo Molina-Luna, Oliver Gutfleisch, Karsten Durst
Summary: Textured nanocrystalline SmCo5-Cu magnets are produced by high-pressure torsion (HPT) of powder blends consisting of SmCo5 and Cu powder. The process overcomes limitations imposed by the phase diagram as in conventional sintering routes, enabling a free selection of the magnetic phase and the grain boundary phase. Increasing number of rotations during HPT leads to structural refinement, increasing coercivity, and amorphous structure of strongly deformed SmCo5 particles. The magnetic hardening is attributed to microstructural refinement and magnetic decoupling of hard magnetic SmCo5 grains by Cu.
Article
Chemistry, Physical
Paul Braun, Philipp Gruetzmacher, Leonie Frohnapfel, Frank Muecklich, Karsten Durst
Summary: In this study, metallic substrates with a nanocrystalline grain size were structured down to the micro-and nanometre range using a room temperature nanoimprinting process. Hard metal dies patterned by Direct Laser Interference Patterning (DLIP) were used to deform the metallic substrates, transferring the pattern onto a nanocrystalline CuZn30 model alloy. The replication process allowed for the formation of separated dimples and LIPSS on the alloy surface.
APPLIED SURFACE SCIENCE
(2023)
Article
Chemistry, Physical
S. Gonzalez, A. K. Sfikas, Spyros Kamnis, S. E. John, Z. W. Nye, M. Spink, C. Allen, R. Martinez-Sanchez, S. W. Naung, M. Rahmati, T. Keil, K. Durst, R. J. Lancaster
Summary: The suitability of determining the strain rate sensitivity (SRS) of the CoCrFeMnNi high-entropy alloy (HEA) by small punch (SP) testing has been assessed. The stress increased with the displacement rate, while the plastic strain distributions were similar. Casting defects caused a drop in strength and ductility at a higher displacement rate. The strain-rate sensitivity exponent (m) was found to be 0.1387, slightly larger than the value predicted by Finite Element Analysis (FEA). The relationship between experimental and predicted properties from the SP tests showed a high level of agreement for maximum stress properties.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Materials Science, Multidisciplinary
Jianing Liu, Ying Yang, Franziska Staab, Carlos Donate-Buendia, Rene Streubel, Bilal Goekce, Fernando Maccari, Philipp Gabriel, Benjamin Zingsem, Detlef Spoddig, Karsten Durst, Michael Farle, Oliver Gutfleisch, Stephan Barcikowski, Konstantin Skokov, Anna R. Ziefuss
Summary: The use of nanoparticle-modified magnetic microparticle powder feedstock can improve the microstructure of suction-cast Nd-Fe-B-based alloys. Ag nanoparticles result in smaller, more uniform grain sizes, while ZrB2 nanoparticles result in uniformly distributed grain sizes at lower mass loadings. This study highlights the potential of using nanoparticles to develop new powder feedstocks for additive manufacturing, improving the final part's properties.
ADVANCED ENGINEERING MATERIALS
(2023)
Article
Materials Science, Multidisciplinary
S. Gonzalez, A. K. Sfikas, S. Kamnis, S. E. John, N. C. Barnard, C. Gammer, J. Eckert, C. G. Garay-Reyes, R. Martinez-Sanchez, S. W. Naung, M. Rahmati, T. Keil, K. Durst, R. J. Lancaster
Summary: High entropy alloys (HEAs) are metallic materials with unique properties due to their chemical composition and atomic arrangement. This research investigated the strain rate sensitivity (SRS) of two HEA CoCrFeMnNiTix (x = 0, 0.3) alloy compositions using shear punch testing. The results showed that only one of the alloy compositions exhibited SRS at room temperature.
MATERIALS & DESIGN
(2023)
Proceedings Paper
Engineering, Electrical & Electronic
Tamira Stegmann, Andre Schwoebel, Wolfgang Schmitt, Stefan Gunst, Karsten Durst, Peter Klar, Nils Neugebauer, Jan Luka Dornseifer
Summary: Low-temperature silver sintering joining technology has become increasingly attractive in power electronics due to the promising properties of silver. The bonding quality of sintered silver not only depends on the microstructure, but also on the interfacial properties to the joining materials. The presence and thickness of copper oxide layers affect the bonding performance, with an optimal bond strength achieved on CuO. However, if the oxide layer becomes too thick, bonding is no longer guaranteed. Higher sintering temperature and pressure result in a denser sintered layer and stronger bonding on copper substrates.
2023 IEEE 73RD ELECTRONIC COMPONENTS AND TECHNOLOGY CONFERENCE, ECTC
(2023)
Proceedings Paper
Metallurgy & Metallurgical Engineering
T. Keil, C. Minnert, E. Bruder, K. Durst
Summary: Two different alloy series were selected to investigate the effects of solutes on the saturation grain size, thermal stability, and mechanical properties after high pressure torsion. The results showed that solutes increase the strength and thermal stability of the alloys, and the grain size is correlated with solid solution hardening.
42ND RISO INTERNATIONAL SYMPOSIUM ON MATERIALS SCIENCE: MICROSTRUCTURAL VARIABILITY: PROCESSING, ANALYSIS, MECHANISMS AND PROPERTIES
(2022)
Article
Materials Science, Ceramics
Chukwudalu Okafor, Kuan Ding, Xiandong Zhou, Karsten Durst, Juergen Roedel, Xufei Fang
Summary: A simple method is reported to mechanically tailor dislocation densities in single-crystal SrTiO3 by increasing the number of indenting cycles using a millimeter-sized Brinell indenter. This approach creates large and crack-free plastic zones over hundreds of micrometers, opening new opportunities in the area of dislocation-tuned functional and mechanical studies.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2022)
