Synergistic effects of deep cryogenic treatment and aging on microstructure and mechanical properties of (FeCoNi)86Al7Ti7 high-entropy alloy

Abstract

The influence of deep cryogenic treatment (DCT) on the microstructure and mechanical properties of the (FeCoNi)₈₆Al₇Ti₇ high-entropy alloy (HEA) was systematically investigated. Combination of aging and the DCT treatments resulted in notable changes in grain size, phase morphology, and mechanical performance of the alloy. Incorporating DCT (with two complete cycles of holding at − 196 °C for 12 h followed by warming to 30 °C for 1 h) refined the grain size and also increased the volume fraction of L1₂ precipitates with their size reduced and their morphology altered. Aging at 720 °C produced spherical L1₂ phases, while aging at 820 °C led to a cuboidal morphology, achieving a balance between mechanical strength and thermal stability. Specifically, the yield strength and ductility were improved from 1080 MPa and 5.2% to 1105 MPa and 7.1%, respectively, by DCT prior to aging at 720 °C. However, a slight decrease in ductility from 26.5 to 23.5% was observed when DCT was applied after aging at 820 °C, despite an enhanced yield strength to 1090 MPa. The findings in this study underline DCT’s role in optimizing HEA microstructure, demonstrating its capacity to refine grains, promote uniformity, and boost mechanical performance, and thereby provide valuable insights for tailoring advanced alloys to meet stringent application demands.