Novel as-cast NiAlCoFeNb dual-phase high-entropy alloys with high hardness

Abstract

• A novel class of NiAlCoFeNb HEAs were synthesized by vacuum arc melting. • These HEAs consist of NiAl-rich B2 phase and FeNb-rich hexagonal Laves phase. • The hardness increases with the incremental volume fraction of Laves phase. • The equiatomic Ni 20 Al 20 Co 20 Fe 20 Nb 20 HEA has ultrahigh hardness of ∼ 818 HV. The microstructure, phase constitution and microhardness of Ni 20 Al 20 Co 20 Fe 20 Nb 20 , Ni 25 Al 25 Co 20 Fe 20 Nb 10 and Ni 30 Al 30 Co 20 Fe 15 Nb 5 high-entropy alloys (HEAs) synthesized by vacuum arc melting have been investigated. These as-cast HEAs have a dual-phase structure including intermetallic NiAl-rich B2 phase and FeNb-rich hexagonal Laves phase, and the Nb increase leads to more fraction of Laves phase. Ultrahigh hardness of ∼ 818 HV was achieved in the equiatomic Ni 20 Al 20 Co 20 Fe 20 Nb 20 dual-phase HEA, which is consisted of 61.8 vol% Laves phase and 38.2 vol% B2 phase.