A comparison of the microstructures and hardness values of non-equiatomic (FeNiCo)-(AlCrSiTi) high entropy alloys having thermal histories related to laser direct metal deposition or vacuum remelting

Abstract

Compared with conventional casting process, laser direct metal deposition (LDMD) can effectively reduce component segregation in non-equiatomic high entropy alloys (HEAs). However, the non-equilibrium thermal history imparted by this method has a significant effect on the microstructure and mechanical properties of the HEA. The present work prepared non-equiatomic (FeNiCo)-(AlCrSiTi) HEAs using the LDMD process, after which some samples were subjected to a subsequent vacuum remelting (VRM) treatment. The variations in phase composition, microstructure and hardness between the HEAs processed using the LDMD or VRM methods were investigated. Differences in phase composition increased with increases in the proportion of the Al, Cr, Si and Ti components. Compared with the HEA samples processed using the VRM method, the LDMD specimens possessed much finer and simpler microstructures mainly comprising solid solution phases. At relatively high concentrations of the Al, Cr, Si and Ti components (32 at% and 40 at% in total), the HEAs processed under LDMD conditions had similar grain morphologies, intermetallic phases and microhardness values, while the VRM specimens presented completely different microstructures and properties.