Phase Composition of a CrMo0.5NbTa0.5TiZr High Entropy Alloy: Comparison of Experimental and Simulated Data

Oleg Senkov,Fan Zhang,Jonathan Miller

doi:10.3390/e15093796

Oleg Senkov, Fan Zhang + Show 1 more

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https://doi.org/10.3390/e15093796

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Abstract

Microstructure and phase composition of a CrMo0.5NbTa0.5TiZr high entropy alloy were studied in the as-solidified and heat treated conditions. In the as-solidified condition, the alloy consisted of two disordered BCC phases and an ordered cubic Laves phase. The BCC1 phase solidified in the form of dendrites enriched with Mo, Ta and Nb, and its volume fraction was 42%. The BCC2 and Laves phases solidified by the eutectic-type reaction, and their volume fractions were 27% and 31%, respectively. The BCC2 phase was enriched with Ti and Zr and the Laves phase was heavily enriched with Cr. After hot isostatic pressing at 1450 °C for 3 h, the BCC1 dendrites coagulated into round-shaped particles and their volume fraction increased to 67%. The volume fractions of the BCC2 and Laves phases decreased to 16% and 17%, respectively. After subsequent annealing at 1000 °C for 100 h, submicron-sized Laves particles precipitated inside the BCC1 phase, and the alloy consisted of 52% BCC1, 16% BCC2 and 32% Laves phases. Solidification and phase equilibrium simulations were conducted for the CrMo0.5NbTa0.5TiZr alloy using a thermodynamic database developed by CompuTherm LLC. Some discrepancies were found between the calculated and experimental results and the reasons for these discrepancies were discussed.

Highlights

A new, high-entropy alloying strategy for the development of high strength and high-temperature alloys has been recently proposed [1,2]
Solidification simulation (Scheil model) results showing the presence of the eutectic reaction with the formation of the BCC2 and Laves phases in the CrMo0.5NbTa0.5TiZr high entropy alloy seem to support the experimental observations and explain the morphology of the microstructure, with the mixture of the BCC2 and Laves phases forming a continuous network between the BCC1 particles
Microstructure and phase composition of a CrMo0.5NbTa0.5TiZr high entropy alloy were studied in the as-solidified condition and after heat treatment at 1450 °C for 3 h and 1000 °C for 100 h

Summary

Introduction

A new, high-entropy alloying strategy for the development of high strength and high-temperature alloys has been recently proposed [1,2]. High configurational entropy of mixing of the alloying elements is believed to stabilize the more ductile disordered solid-solution phases relative to the brittle intermetallic phases. This strategy is based upon the simple thermodynamic argument that random solid-solutions of multi-principal alloying elements will have higher mixing entropies than intermetallic compounds, and will tend to be more stable (i.e., they have a lower Gibbs free energy of formation, G = H − T S). The design and development of HEAs is built upon the fact that high configuration entropy makes a significant contribution to the phase stability of random mixed disordered solution phases. Integration of the calculation of phase diagrams (CALPHAD) approach with key experiments has been used as an effective approach in the determination of complicated multi-component phase diagrams [9]

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