Processing-Driven Chemical Ordering and Its Effect on Magnetic Properties in a High Entropy Alloy

Abstract

The influence of chemical ordering and its length scale on the magnetic behavior of the Al0.2Ti0.3Co1.5CrFeNi1.5 high entropy alloy (HEA) was investigated across three distinct microstructural conditions, including a solution annealed state, an annealed condition at 750 °C, and a cold rolled plus annealed condition. These processing routes produced changes in the volume fraction, size, and morphology of L12 ordered precipitates along with the formation of a minor L21 phase in the annealed states. Magnetic measurements performed between 2 K and 300 K revealed clear differences in saturation magnetization, coercivity, and magnetic transition temperatures across the three conditions. The solution annealed condition exhibited a single magnetic transition near 48 K and low coercivity, consistent with a fine dispersion of coherent L12 precipitates. In the annealed and cold rolled conditions, coarsening and morphological evolution of the L12 phase led to the emergence of a second magnetic transition at lower temperatures, attributed to partial magnetic decoupling of the precipitates. Coercivity increased significantly in these conditions due to enhanced domain wall pinning, while residual hysteresis at 300 K is attributed to a combination of minor L21 phase at grain boundaries and microstructural features in the cold-worked condition. These results demonstrate that chemical ordering and its structural evolution play a central role in governing low temperature magnetic behavior in this alloy system. The findings contribute to the broader understanding of multifunctional HEA that combine tunable magnetic properties with excellent mechanical performance.