Thermodynamically Driven Evolution of Coherent BCC/B2 Microstructures and Their Impact on Mechanical Properties in an Al‐Containing Multiprincipal Element Alloy

Abstract

A novel Al 1.5 Ti 6.5 Zr 2 Nb 3 Ta 2 Mo 0.5 Cr 0.5 multiprincipal element alloy (MPEA) with a coherent BCC/B2 microstructure containing cuboidal BCC precipitates was designed. The microstructural evolution and corresponding mechanical properties under different heat‐treatment conditions were systematically investigated. After aging at 873 K, a coherent BCC/B2 microstructure is formed, exhibiting an excellent combination of high yield strength (~1200 MPa) and good compressive plasticity (~50%). This good mechanical performance is attributed to the cooperative deformation of kink bands and the BCC/B2 microstructure, where dislocation shearing of ordered B2 phase and the associated structure formation provide effective strengthening while maintaining plastic deformability. With increasing aging temperature to 973–1073 K, the B2 phase becomes thermodynamically unstable, leading to the precipitation of hexagonal Al 3 Zr 5 phases and subsequently (Al, Cr) 2 Zr Laves phases, accompanied by a degradation in both strength and ductility. High‐temperature compression tests reveal that the 873 K‐aged alloy retains a relatively high strength (~912 MPa) at 873 K, whereas a pronounced softening occurs at higher temperatures due to the transformation into a single BCC solid solution driven by enhanced elemental solubility. This work highlights the critical role of coherent BCC/B2 microstructures in governing both strengthening and deformation mechanisms in MPEAs.