Strengthening and Toughening of the Co34Cr32Ni27Al3.5Ti3.5 Alloy Through Coherent L12 Nanoprecipitates

Abstract

Herein, the L12‐strengthened Co34Cr32Ni27Al3.5Ti3.5 medium‐entropy alloy (MEA) with outstanding strength and ductility is developed through cold rolling and annealing (CRA). The CRA promotes the formation of coherent L12 nanoprecipitates in the matrix and precipitates inside the grains (Ti‐rich phases), resulting in dislocation sliding and multiplication during deformation. The as‐cast sample exhibits low yield strength (YS) of ≈498.5 MPa, ultimate tensile strength (UTS) of ≈820.5 MPa, and uniform elongation (UE) of ≈29.8%. After cold rolling and annealing, the YS, UTS, and UE are significantly increased to ≈678.4, ≈1109.3 MPa, and ≈44.5%, respectively. The excellent mechanical performance results from dislocation strengthening and precipitation strengthening of the L12 phase. The trade‐off of strength‐ductility is resolved by achieving an appropriate balance between the hard phase rich in L12/Ti and the soft face‐centered cubic phase. This finding demonstrates that the CRA method can be used to create coherent L12 nanoprecipitates that are beneficial for strong and ductile MEA. This work provides a broader perspective for CoCrNi‐based MEAs with high performance in the future.