Microstructural evolution and duplex structure-enhanced high-temperature mechanical properties of Al-doped VCoNi medium entropy alloy

Abstract

The microstructures and mechanical properties of 7 at% Al-added VCoNi medium entropy alloy are studied and compared with those of the undoped alloy at various temperatures. Doping Al promotes the formation of a microstructure composed of the FCC matrix and the BCC-L21 phase, which remains stable until the matrix gradually transforms into the HCP-к and tetragonal-σ phases after 600 °C. Compared with the VCoNi alloy, the differences involve that the Al addition suppresses the strain-induced FCC-HCP transformation at 25 °C, and delays the eutectoid reaction at 700 °C. Corresponding to the microstructure evolution, the doped alloy preserves higher strength and strain hardening capacity until 600 °C due to the high-content harder BCC phase but comparable values at 700 and 800 °C with the relatively less HCP phase. Besides, the added Al can also reduce the susceptibility to the serration flow. The results reveal that the (VCoNi)93Al7 alloy has high potentials for intermediate-temperature applications.