Development and characterization of novel Ni-rich high-entropy alloys

Abstract

The novel Ni-rich high-entropy alloys (HEAs) of Ni40Fe30Co20Al10 (Ti-0) and (Ni40Fe30Co20Al10)90Ti10 (Ti-10) consisting of dendritic structures were designed and fabricated by vacuum arc-melting. As-cast Ti-0 HEA shows a single FCC phase (γ), whereas Ti addition induces the precipitation of BCC phase from γ matrix in interdendrite region of Ti-10 HEA. However, the γ matrix in dendrite region is filled with large amounts of multi-elemental L12 nanoparticles (γʹ) with sizes around 40 nm and 160 nm. Despite the high microhardness and wear resistance, Ti-10 shows unexpected tensile properties. It is mainly attributed to the selective location and huge size difference of γʹ precipitations. However, it is interesting that the as-cast Ti-0 HEA exhibits good strength-ductility combination as benchmarked with state-of-the-art single-FCC HEAs prepared by casting alone. It is rationalized by the distinct three-stage work-hardening behavior, dense dislocation walls formed along the γ phase boundary, and semi-coherence boundaries in the as-cast Ti-0 HEA. Compared with 304L steel and Ti-0 HEA, the Ti-10 HEA presents good comprehensive corrosion resistance in seawater solution. Ti addition is favorable for the formation of passivation film.