Realistic microstructure evolution of complex Ta-Nb-Hf-Zr high-entropy alloys by simulation techniques

Abstract

Over last 15 years high-entropy alloys (HEAs) and complex concentrated alloys (CCAs) have gained much appreciation for their numerous superior properties. In this paper we have shown a novel simulation methodology to realistically predict the nanometer level local structural features of complex Ta0.25Nb0.25Hf0.25Zr0.25 HEA. This involves prediction of the morphology of the short-range clustering (SRCs), their quantitative atomic composition at the nano level and the thermodynamic aspects. An alloy structure model containing 11664 atoms was created and this was subjected to structure evolution at 1800 °C. The structure evolution technique is based on a combined hybrid Monte Carlo and molecular dynamics (MC/MD) approach. The simulated results from this work are further validated against experiments and material characterizations reported in literature and done by high-resolution transmission electron micrograph (HRTEM) for the nano-level microstructure, atom probe tomography (APT) for the local chemical compositions and X-ray diffraction at synchrotron sources for the local lattice relaxation effects. This work qualitatively and quantitatively reproduces the materials characterization results reasonably well from the developed simulation methodologies. The structure evolution methods as described in this work are based on independent computer simulations and does not involve any manual intervention for input based on experiments on evolving SRCs. This work shows the potential of utilizing MC/MD based computational methods to reduce the number of costly experimental characterizations and accelerate the pace for materials development.

Computational property predictions of Ta–Nb–Hf–Zr high-entropy alloys

“…As this is the situation experienced by the dislocations causing yielding and plastic deformation in dislocation pile-up and crack tip propagation, the high stress simulations indicate a low degree of expected ductility for the 15 MC swap structure. This is getting reflected in experiment on the very low ductility of below 1% for the 1-day annealed alloy, which in term resembles the 15 MC swap evolved structure of this study and the previous study on structure evolution 19 .…”

“…The resultant elastic constants from the EAM potential for the elements are compared against the input elastic constant in Table 1 of our previous publication in Ref. 19 and found to correlate well. The LAMMPS readable format of the EAM potential file for the Ta–Nb–Hf–Zr system can be found in the Materials Cloud Archive 37 .…”

“…The application of computational techniques to predict the properties of R-HEAs could provide an alternative to tedious experiments. In literature there had been some effort to computationally predict some of the properties of TaNbHfZr R-HEAs like the sequential nanostructure evolution, nature of SRO/SRC and local lattice distortions 19 . But the domain size of the simulated R-HEA system was rather small and the hybrid Monte Carlo/Molecular Dynamics (MC/MD) based thermodynamic properties were only limited to change in enthalpy.…”

“…The simulations for this study are done with the help of EAM potentials as also used in Ref. 19 for the same TaNbHfZr alloy system.…”

Microstructures and Properties of High‐Entropy Materials: Modeling, Simulation, and Experiments

“…There is even a small amount of twin appearing, resulting in the increased ductility of BCC HEAs, while the strength may reduce. [ 177–180 ] Therefore, similar to traditional metals, the low strength in HEAs is still a problem that needs to be solved urgently.…”