More Like this

1. Cross-kinks control screw dislocation strength in equiatomic bcc refractory alloys

   Zhou, X. ; He, S. ; Marian, J. ( April 2021 , Acta materialia)

   null (Ed.)

   Refractory multi-element alloys (RMEA) with body-centered cubic (bcc) structure have been the object of much research over the last decade due to their high potential as candidate materials for high- temperature applications. Most of these alloys display a remarkable strength at high temperatures, which cannot be explained by the standard model of bcc plasticity based on thermally-activated screw disloca- tion motion. Several works have pointed to chemical energy fluctuations as an essential aspect of RMEA strength that is not captured by standard models. In this work, we quantify the contribution of screw dis- locations to the strength of equiatomic Nb-Ta-V alloys using a kinetic Monte Carlo model fitted to solu- tion energetics obtained from atomistic calculations. In agreement with molecular dynamics simulations, we find that chemical energy fluctuations along the dislocation line lead to measurable concentrations of kinks in equilibrium in a wide temperature range. A fraction of these form cross-kink configurations, which are ultimately found to control screw dislocation motion and material strength. Our simulations (i) confirm that the evolution of cross kinks and self-pinning are strong contributors to the so-called ‘cocktail’ effect in this alloy at low temperature, and (ii) substantiate the notion that screw dislocation plasticity alone cannot explain the high temperature strength of bcc RMEA. 

   more » « less
2. Effects of local compositional and structural disorder on vacancy formation in entropy-stabilized oxides from first-principles

   https://doi.org/10.1038/s41524-022-00780-0  

   Chae, Sieun ; Williams, Logan ; Lee, Jihang ; Heron, John T. ; Kioupakis, Emmanouil ( April 2022 , npj Computational Materials)

   Entropic stabilization has evolved into a strategy to create new oxide materials and realize novel functional properties engineered through the alloy composition. Achieving an atomistic understanding of these properties to enable their design, however, has been challenging due to the local compositional and structural disorder that underlies their fundamental structure-property relationships. Here, we combine high-throughput atomistic calculations and linear regression algorithms to investigate the role of local configurational and structural disorder on the thermodynamics of vacancy formation in (MgCoNiCuZn)O-based entropy-stabilized oxides (ESOs) and their influence on the electrical properties. We find that the cation-vacancy formation energies decrease with increasing local tensile strain caused by the deviation of the bond lengths in ESOs from the equilibrium bond length in the binary oxides. The oxygen-vacancy formation strongly depends on structural distortions associated with the local configuration of chemical species. Vacancies in ESOs exhibit deep thermodynamic transition levels that inhibit electrical conduction. By applying the charge-neutrality condition, we determine that the equilibrium concentrations of both oxygen and cation vacancies increase with increasing Cu mole fraction. Our results demonstrate that tuning the local chemistry and associated structural distortions by varying alloy composition acts an engineering principle that enables controlled defect formation in multi-component alloys.

    

   more » « less
3. Modeling environment-dependent atomic-level properties in complex-concentrated alloys

   https://doi.org/10.1063/5.0076584  

   Farnell, Mackinzie S. ; McClure, Zachary D. ; Tripathi, Shivam ; Strachan, Alejandro ( March 2022 , The Journal of Chemical Physics)

   Complex-concentrated-alloys (CCAs) are of interest for a range of applications due to a host of desirable properties, including high-temperature strength and tolerance to radiation damage. Their multi-principal component nature results in a vast number of possible atomic environments with the associated variability in chemistry and structure. This atomic-level variability is central to the unique properties of these alloys but makes their modeling challenging. We combine atomistic simulations using many body potentials with machine learning to develop predictive models of various atomic properties of CrFeCoNiCu-based CCAs: relaxed vacancy formation energy, atomic-level cohesive energy, pressure, and volume. A fingerprint of the local atomic environments is obtained combining invariants associated with the local atomic geometry and periodic-table information of the atoms involved. Importantly, all descriptors are based on the unrelaxed atomic structure; thus, they are computationally inexpensive to compute. This enables the incorporation of these models into macroscopic simulations. The models show good accuracy and we explore their ability to extrapolate to compositions and elements not used during training. 

   more » « less
4. Multiplicity of dislocation pathways in a refractory multiprincipal element alloy

   https://doi.org/10.1126/science.aba3722  

   Wang, Fulin ; Balbus, Glenn H. ; Xu, Shuozhi ; Su, Yanqing ; Shin, Jungho ; Rottmann, Paul F. ; Knipling, Keith E. ; Stinville, Jean-Charles ; Mills, Leah H. ; Senkov, Oleg N. ; et al ( October 2020 , Science)

   Refractory multiprincipal element alloys (MPEAs) are promising materials to meet the demands of aggressive structural applications, yet require fundamentally different avenues for accommodating plastic deformation in the body-centered cubic (bcc) variants of these alloys. We show a desirable combination of homogeneous plastic deformability and strength in the bcc MPEA MoNbTi, enabled by the rugged atomic environment through which dislocations must navigate. Our observations of dislocation motion and atomistic calculations unveil the unexpected dominance of nonscrew character dislocations and numerous slip planes for dislocation glide. This behavior lends credence to theories that explain the exceptional high temperature strength of similar alloys. Our results advance a defect-aware perspective to alloy design strategies for materials capable of performance across the temperature spectrum.

    

   more » « less
5. High‐Throughput Computational Characterization of 2D Compositionally Complex Transition‐Metal Chalcogenide Alloys

   https://doi.org/10.1002/adts.202000195  

   Wang, Duo ; Liu, Lei ; Basu, Neha ; Zhuang, Houlong L. ( October 2020 , Advanced Theory and Simulations)

   2D binary transition‐metal chalcogenides (TMCs) such as molybdenum disulfide exhibit excellent properties required for energy conversion applications. Alloying binary TMCs can form 2D compositionally complex TMC alloys (CCTMCAs) that possess remarkable properties from the constituent TMCs. High‐throughput workflow performing density functional theory (DFT) calculations based on the virtual crystal approximation (VCA) model (VCA‐DFT) is designed. The workflow is tested by predicting properties including in‐plane lattice constants, band gaps, effective masses, spin–orbit coupling, and band alignments of the Mo‐W‐S‐Se, Mo‐W‐S‐Te, and Mo‐W‐Se‐Te 2D CCTMCAs. The VCA‐DFT results are validated by computing the same properties using unit cells and supercells of selected compositions. The VCA‐DFT results of the abovementioned five properties are comparable to that of DFT calculations, with some inaccuracies in several properties of MoSTe and WSTe. Moreover, 2D CCTMCAs can form type II heterostructures as used in photovoltaics. Finally, Mo_0.5W_0.5SSe, Mo_0.5W_0.5STe, and Mo_0.5W_0.5SeTe 2D CCTMCAs are used to demonstrate the room‐temperature entropy‐stabilized alloys. They also exhibit high electrical conductivities at 300 K, promising for light adsorption devices. This work shows that the high‐throughput workflow using VCA‐DFT calculations provides a tradeoff between efficiency and accuracy, opening up opportunities in the computational design of other 2D CCTMCAs for various applications.

    

   more » « less