Effect of Ni3Ti on strength improvement in corrosion resistant Ni40Fe32Cr20Ti4Mo4 High-entropy alloy

摘要

Due to the exhibited promising comprehensive properties [1], High-entropy alloys (HEAs) has received increasing attention ever since it was first reported. Among various HEAs, precipitation -hardened HEAs (PH -HEAs) has exhibited outstanding mechanical properties. The extensively studied HEAs hardened by secondary phases such as L12 and B2 phase have high-strength and large-ductility at room temperature. However, secondary phase in most reported HEAs with good strength and ductility usually contains harmful elements to corrosion resistance, such as Al [2], and the application was restricted. Ni 3Ti phase eliminates the negative effect of Al on passive film and has good strength and plasticity. Different from the widely studied corrosion behavior of B2 [3] and L1 2 phase [4], Ni 3Ti phase received little concern. To design corrosion resistan t Ni 3Ti-hardened HEAs, it is necessary to study its corrosion behaviour. In this work, Ni3Ti-hardened Ni40Fe32Cr20Ti4Mo4 HEA (Ti4Mo4) was designed, and was produced via inductive arc melting furnace. Spherical Ni3Ti phase (SNPs, enriched in Ni, Ti with minor Fe and Cr) precipitated at grain interior, lamella Ni3Ti phase (LNPs, enriched in Ni and Ti) precipitated at partial grain boundary. Effect of Ni 3Ti phase in Ti4Mo4 on corrosion resistance and passive film properties in 15 wt.% NaCl, as well as mechanic al properties and crack initiation during tensile was investigated. Transpassivation potential of Ti4Mo4 reached 1.05 mVSCE, ultimate tensile stress was 1189 MPa, elongation was 27%. The continuous and protective passive film on whole surface resulted in t he good corrosion resistance, and no pits formed. The plastic deformation ability of Ni3Ti phase contributed to the good mechanical properties.