Ubiquitous short-range order in multi-principal element alloys

TL;DR

This study reveals that short-range order (SRO) in multi-principal element alloys (MPEAs) is an inherent feature formed during solidification, largely unaffected by processing conditions, which impacts how we can engineer these materials for desired properties.

Contribution

The paper demonstrates that SRO in MPEAs forms during solidification and is insensitive to cooling rates and thermal treatments, providing new insights into SRO formation mechanisms.

Findings

SRO levels are similar across different processing conditions.

Atomistic simulations confirm SRO forms during rapid solidification.

SRO is an inherent characteristic of most MPEAs.

Abstract

Recent research in multi-principal element alloys (MPEAs) has increasingly focused on the exploration and exploitation of short-range order (SRO) to enhance material performance. However, the understanding of SRO formation and the precise tuning of it within MPEAs remains poorly understood, limiting the comprehension of its impact on material properties and impeding the advancement of SRO engineering. Here, leveraging advanced additive manufacturing techniques that produce samples with a wide range of cooling rates (up to 10^7 K/s) and an improved quantitative electron microscopy method, we characterize SRO in three CoCrNi-based MPEAs to unravel the role of processing route and thermal history on SRO. Surprisingly, irrespective of the processing and thermal treatment applied, all samples exhibit similar levels of SRO, suggesting that prevalent SRO may form during the solidification process. Atomistic simulations of solidification verify that local chemical ordering arises in the liquid-solid interface (solidification front) even under the extreme cooling rate of 10^11 K/s. This phenomenon stems from the swift atomic diffusion in the supercooled liquid, which matches or even surpasses the rate of solidification. Therefore, SRO is an inherent characteristic of most MPEAs, insensitive to variations in cooling rates and annealing treatments typically available in experiments. Integrating thermal treatment with other strategies, such as mechanical deformation and irradiation, might be more effective approaches for harnessing SRO to achieve controlled material properties.