Chemical short-range orders and the induced structural transition in high-entropy alloys

Abstract

The chemical short-range orders (CSROs) of high entropy alloys (HEAs) play an important role in their structural transitions and advanced properties. However, it is difficult to describe the CSROs with local atomic structures. The present work introduces a cluster-plus-glue-atom model to understand the CSROs of Al-Ni-Co-Fe-Cr HEAs. This model dissociates the solid-solution structure into a cluster part and a glue atom part, as expressed with a uniform composition formula of [cluster](glue)m. Two HEAs with a composition of Al2M14 (M presents different combinations of transition metals) are designed, which is derived from two cluster models of [Al-M12](M2Al1) in the FCC structure and [Al-M14]Al1 in the BCC structure. M = Ni4Co4Fe3Cr3 renders the HEA with a FCC-based structure, while the matrix will be transformed into a BCC structure when M = Ni1Co1Fe2Cr1. These two cluster models are then used to simulate the pair distribution function (PDF) at short inter-atomic distances. The calculated PDFs within the frame of cluster models can describe experimental neutron PDFs better than ones based on the average crystal structures. It provides a clear indication of the existence of CSROs in HEAs and proves fesability of the cluster structural model. This cluster model demonstrates a novel way to understand the CSROs and the induced structural transition due to the local lattice distortion, which would be developed into a new alloy design strategy for high-performance HEAs.