EFFECT OF ANNEALING ON THE MICROSTRUCTURE AND HARDNESS OF THE FeCoNiCrAl0.25Mn0.75 HIGH ENTROPY ALLOY

Abstract

In this study, the effect of annealing treatment on the microstructural evolution and hardness of the FeCoNiCrAl_0.25Mn_0.75 high-entropy alloy was systematically investigated. The alloy was examined in the as-cast condition and after annealing at 600, 700, and 800°C for 4, 8, 16, and 24 h, respectively. The as-cast microstructure primarily consisted of a FeCoNi-rich FCC solid solution accompanied by a minor fraction of an AlNi-rich BCC phase. The precipitation of needle-like AlNi-rich BCC phases within the FCC matrix was initiated after annealing at 600°C for 16 h, whereas similar precipitates were observed after only 4 h at annealing temperatures of 700 and 800°C. The volume fraction of the precipitated phase increased progressively with annealing time at all investigated temperatures, reaching a maximum value of approximately 52% under the 800°C/24 h condition. This pronounced precipitation behavior contributed significantly to the strengthening of the alloy, resulting in a maximum hardness of about 205 HV3, compared to 139 HV3 in the as-cast state. These results demonstrate that annealing treatment plays a crucial role in tailoring the microstructure and enhancing the mechanical performance of the FeCoNiCrAl_0.25Mn_0.75 high-entropy alloy, providing valuable insights for the design and development of structural materials.