Computationally-driven engineering of sublattice ordering in a hexagonal AlHfScTiZr high entropy alloy

Lukasz Rogal,Fritz Körmann,Piotr Bobrowski,Blazej Grabowski,Sergiy Divinski,Frank Stein

doi:10.1038/s41598-017-02385-w

Abstract

Multi-principle element alloys have enormous potential, but their exploration suffers from the tremendously large range of configurations. In the last decade such alloys have been designed with a focus on random solid solutions. Here we apply an experimentally verified, combined thermodynamic and first-principles design strategy to reverse the traditional approach and to generate a new type of hcp Al-Hf-Sc-Ti-Zr high entropy alloy with a hitherto unique structure. A phase diagram analysis narrows down the large compositional space to a well-defined set of candidates. First-principles calculations demonstrate the energetic preference of an ordered superstructure over the competing disordered solid solutions. The chief ingredient is the Al concentration, which can be tuned to achieve a D019 ordering on the hexagonal lattice. The computationally designed D019 superstructure is experimentally confirmed by transmission electron microscopy and X-ray studies. Our scheme enables the exploration of a new class of high entropy alloys.

Highlights

Alloy design by combining multiple elements in near-equimolar ratios has the potential of creating new, unique engineering materials, commonly known as high entropy alloys (HEAs) or multi-principal element alloys[1,2,3,4,5]
Even if a parametrization was available, it could not be guaranteed that it provides a reasonable description of the HEA system for which it has not been optimized
In particular we investigate whether an ordered D019 superstructure can be energetically stable over the fully disordered hcp A3 and bcc A2 solid solutions, which are the most relevant phases according to the above phase diagram analysis

Summary

Introduction

Alloy design by combining multiple elements in near-equimolar ratios has the potential of creating new, unique engineering materials, commonly known as high entropy alloys (HEAs) or multi-principal element alloys[1,2,3,4,5]. The original idea behind this concept is to maximize the configurational entropy to achieve a single phase disordered solid solution Such concentrated disordered solutions have been shown to exist on the face-centered cubic (fcc) and body-centered cubic (bcc) lattice[1,2,3], and more recently on the hexagonal close-packed (hcp) lattice[23,24,25,26]. Just one atomic species could reveal a preference to a given sublattice whereas all other atoms may be distributed As this comment should make clear, a large number of potential types of ordering is possible in HEAs, thereby opening new perspectives for alloy optimization and development. We apply this strategy to the Al-Hf-Sc-Ti-Zr system with the goal of finding a new HEA with an ordered D019 superstructure on the hcp lattice

Methods

Results

Conclusion