# Al-Induced Unusual Grain Growth in Ni-Co-Cr Multi-Principal Element Alloys

## TL;DR

This paper investigates how adding aluminum to a specific type of alloy causes unusual grain growth, and how other elements like tungsten and molybdenum can counteract this effect.

## Contribution

The study reveals how substitutional Al affects grain boundary mobility and how W and Mo can suppress Al-induced grain growth in multi-principal element alloys.

## Key findings

- Al reduces activation energy for grain growth, enhancing grain boundary mobility.
- W and Mo increase activation energy and inhibit Al-induced grain growth.
- Al-induced grain growth has a lower activation energy of 219 kJ/mol compared to 251 kJ/mol with W and Mo.

## Abstract

Substitutional elements are introduced to face-centered cubic (FCC) multi-principal element alloys (MPEAs) to effectively enhance the mechanical performance by solid solution strengthening and second-phase strengthening. Commonly, relatively large atomic radius elements introduced into the alloy matrix result in lattice distortion and hinder grain boundary migration, thus achieving matrix strengthening. However, owing to the complex compositions of MPEAs, different substitutional elements introduced affect the microstructure evolution behavior and corresponding strengthening effects. In this work, an abnormal grain growth behavior of Ni-Co-Cr-based MPEAs based on Al alloying was observed. Systematic annealing experiments combined with quantitative grain growth analysis were conducted to clarify the effects of Al, W, and Mo on grain boundary migration. The results show that substitutional Al reduces the apparent activation energy for grain growth, resulting in both a lower grain growth component (n = 2) and a lower activation energy for grain growth of 219 kJ/mol, thereby enhancing grain boundary mobility. On the contrary, minor additions of high-melting-point W and Mo effectively inhibited the Al-induced rapid grain growth by increasing the activation energy and resulting in a higher grain growth component and a lower activation energy for grain growth of 251 kJ/mol. These findings provide new insights into the role of substitutional solutes in controlling grain growth kinetics in multi-principal element alloys.