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.
Highlights
Over last 15 years high-entropy alloys (HEAs) and complex concentrated alloys (CCAs) have gained much appreciation for their numerous superior properties
To overcome this difficulty of dealing with tiny lengthscale and timescales involved in density functional theory (DFT) and molecular dynamics (MD) techniques, some accelerated dynamics techniques were developed in combination with Monte Carlo based MD (MC/MD) techniques[23]
Near the node the short-range clustering (SRCs) look like forming a cross-type pattern, which was experimentally found in the system during annealing treatment at 1800 °C as characterized by highresolution transmission electron micrograph (HRTEM) and APT19
Summary
Over last 15 years high-entropy alloys (HEAs) and complex concentrated alloys (CCAs) have gained much appreciation for their numerous superior properties. It was generally found that the different types of hybrid sequential or mixed MC/MD techniques can accelerate the dynamics by a factor of 107, which would transform the dynamics timescale of MD simulation from the nanosecond/ microsecond to the more practical and realistic seconds timescale[23] Inspired by these MC/MD methodologies, ab-initio based MC/MD simulations were tried on HEAs for the theoretical investigation of SRO/ SRC effects, prediction of equilibrium intermetallic phases and limited information about lattice distortion effects by Widom et al in recent years[24,25]. We have computationally studied equimolar TaNbHfZr HEA for its nanostructure morphology evolution for high-temperature annealing, evolution of SRO/SRC, local lattice relaxations, which closely validates these structural characteristics obtained from the abovementioned high-end experimentations like HRTEM, APT and synchrotron XRD19. MC/MD technique with EAM type MD potentials were utilized in this work
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