Enhancing the mechanical properties of TiZr-based multi-principal element alloys via leveraging multiple short-range orders: an atomic-scale study

Chemical short-range order (SRO) in multi-principal element alloys (MPEAs) and its unprecedented benefits on materials performance have been elucidated in recent experimental observations. Hence, manipulating the fine structure of SRO and its interaction with other coexisting SROs or defects becomes increasingly crucial for MPEAs design. Here, using TiZrNb, TiZrVNb, and TiZrV as the model systems, SRO and its interaction with surrounding environment, as well as its effects on mechanical properties are comprehensively explored through density functional theory-based Monte Carlo simulations. We find that both TiZrNb and TiZrVNb exhibit Ti-Zr SRO and Nb-Nb short-range clustering (SRC), whereas in TiZrV, Zr-V SRO occurs in addition to Ti-Zr SRO. SRO largely increases the modulus and the unstable stacking fault energy (USFE). At the electronic scale, SRO is found accompanied with a deeper pseudo-energy gap at Fermi level, and with a covalent bonding character between the metallic atoms. Due to the SRO-oxygen attraction, oxygen centered and Ti/Zr enriched octahedron coined as (O, 2Ti, 4Zr)-octahedron populates in TiZrNb-O and TiZrV-O. In TiZrVNb-O, there mainly exist two types of octahedral: (O, 2Ti, 4Zr) and (O, 3Ti, 3Zr). Quantitatively, forming these (O, Ti, Zr)-octahedra, the modulus and USFE of MPEAs are further increased compared to the individual contribution from SRO or oxygen, but the improvement does not surpass the sum of the increments induced by the two individuals. The present findings deepen the understanding of SROs and their interactions with surrounding environments, pushing forward the effective utilization of SRO in materials design.