Refractory complex concentrated alloys, composed of multiple principal refractory elements, are promising candidates for high-temperature structural applications due to their exceptional thermal stability and high melting points. However, their mechanical performance is often compromised by interstitial impurities, particularly oxygen, nitrogen, and carbon, which segregate to grain boundaries and promote embrittlement. In this study, we investigate the solubility and thermodynamic behavior of oxygen interstitials in a model NbTiHfTa RCCA system. We synthesized NbTiHfTa alloys with varying oxygen contents via plasma arc melting and characterized their phase evolution and microstructure using XRD, SEM, and TEM. Complementary computational modeling was performed using machine-learning interatomic potentials integrated with Monte Carlo simulations to probe oxygen interactions at the atomic scale. Our results reveal a solubility limit for oxygen between 0.8 and 1.0 atomic percentage, beyond which HfO2 formation is energetically favorable. This combined experimental-computational framework provides a predictive approach for managing interstitial behavior in RCCAs, enabling improved alloy design strategies for enhanced mechanical performance.
Determinants of Self-Interstitial Energetics in Refractory High-Entropy Alloys
Key Laboratory of Automobile Materials (Jilin University), Ministry of Education, Department of Materials Science and Engineering, Jilin University（吉林大学汽车材料教育部重点实验室，材料科学与工程学院）
Plasticity in body centered cubic (bcc) refractory metals are largely due to the stress tensor induced either by solute or thermal activation. The mechanism of the solute atom(s) residence causes instability in such metals. Earlier research have considered the mechanism of oxygen (O) or carbon (C) in tungsten (W), even though the major component of the environment is nitrogen (N). In this article, the density functional theory (DFT) was employed to investigate the thermodynamic stable site for an interstitial solute (N or O) in the bcc refractory metals (Mo and Nb) by calculating the equilibri…
We develop a fast and accurate machine-learned interatomic potential for the Mo-Nb-Ta-V-W quinary system and use it to study segregation and defects in the body-centred cubic refractory high-entropy alloy MoNbTaVW. In the bulk alloy, we observe clear ordering of mainly Mo-Ta and V-W binaries at low temperatures. In damaged crystals, our simulations reveal clear segregation of vanadium, the smallest atom in the alloy, to compressed interstitial-rich regions like radiation-induced dislocation loops. Vanadium also dominates the population of single self-interstitial atoms. In contrast, due to its…
Enhanced Elevated-Temperature Strength in Refractory Complex Concentrated Alloys via Temperature-Induced Transition from Screw-to-Edge Dislocation Control
University of California, Davis（加州大学戴维斯分校）；Oak Ridge National Laboratory（橡树岭国家实验室）；University of Tennessee, Knoxville（田纳西大学诺克斯维尔分校）
The ability to predict the composition- and temperature-dependent stability of refractory complex concentrated alloys (RCCAs) is vital to the design of high-temperature structural alloys. Here, we present a model based on first-principles calculations to predict the thermodynamic stability of multicomponent equimolar solid solutions in a high-throughput manner and apply it to screen over 20,000 compositions. We develop a database that contains pairwise mixing enthalpy of 17 refractory metals using density-functional theory (DFT)-based total energy calculations. To these, we fit thermodynamic s…
Effect of cold rolling strain on the microstructural evolution in equimolar MoNbTaTiZr refractory complex concentrated alloy: Comprehensive characterization
Sluggish and Chemically-Biased Interstitial Diffusion in Concentrated Solid Solution Alloys: Mechanisms and Methods
City University of Hong Kong（香港城市大学）；City University of Hong Kong Shenzhen Research Institute（香港城市大学深圳研究院）；Hong Kong Institute for Advanced Study, City University of Hong Kong（香港城市大学香港高等研究院）
High-entropy alloys (HEAs) with concentrated solid solutions are conceived to possess a rugged atomic and energy landscape in which dislocation motion necessarily proceeds to accommodate mechanical deformation. Fundamental questions remain as to how rough the energy landscape is and to what extent it can be influenced by the local ordering of their constituent elements. Here, we construct and report the potential energy landscape (PEL) governing screw dislocation motion in refractory HEAs that reveals a hierarchical and multilevel structure with a collection of small basins nested in large met…
Using ab initio calculations and special quasirandom structures, we have characterized the distribution of defect formation energy and migration barrier in Ni-based solid-solution alloys: Ni_{0.5}Co_{0.5}, Ni_{0.5}Fe_{0.5}, Ni_{0.8}Fe_{0.2} and Ni_{0.8}Cr_{0.2}. As defect formation energies depend sensitively on elemental chemical potential, we have developed a computationally efficient method for determining it which takes into account the global composition and local short-range order. We find that Fe has the biggest alloy effects for Ni among these four elements. Our results show that the d…
Interfacial segregation and chemical short-range ordering influence the behavior of grain boundaries in complex concentrated alloys. In this study, we use atomistic modeling of a NbMoTaW refractory complex concentrated alloy to provide insight into the interplay between these two phenomena. Hybrid Monte Carlo and molecular dynamics simulations are performed on columnar grain models to identify equilibrium grain boundary structures. Our results reveal extended near-boundary segregation zones that are much larger than traditional segregation regions, which also exhibit chemical patterning that b…
Point defects in body-centred cubic Fe, Cr and concentrated random magnetic Fe-Cr are investigated using density functional theory and theory of elasticity. The volume of a substitutional Cr atom in ferromagnetic bcc Fe is approximately 18\% larger than the volume of a host Fe atom, whereas the volume of a substitutional Fe atom in antiferromagnetic bcc Cr is 5\% smaller than the volume of a host Cr atom. Elastic dipole $\boldsymbol{P}$ and relaxation volume $\boldsymbolΩ$ tensors of vacancies and self-interstitial atom (SIA) defects exhibit large fluctuations, with vacancies having negative a…
Nanoindentation induced plasticity in equiatomic MoTaW alloys by experimentally guided machine learning molecular dynamics simulations
National Centre for Nuclear Research, NOMATEN CoE（国家核研究中心，NOMATEN卓越中心）；Institute for Technology of Nuclear and Other Mineral Raw Materials（核及其他矿物原料技术研究所）
Modeling the Equilibrium Vacancy Concentration in Multi-Principal Element Alloys from First-Principles
École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院）；Institute of Materials, École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院材料研究所）；Laboratory of materials design and simulation (MADES), Institute of Materials, École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院材料研究所材料与模拟实验室）；National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院新材料计算设计与发现国家中心）
