Formation, structure and properties of pseudo-high entropy clustered bulk metallic glasses

Abstract

The formation, structure and properties of clustered glassy alloys were reviewed in correlation with pseudo-high entropy (PHE) type alloy components on the basis of our recent data. The features of the PHE bulk metallic glasses (BMGs) in Fe- and Zr-based alloy systems were also presented in comparison with high entropy glassy and crystalline alloys. The selection of PHE alloy compositions enables the formation of a clustered glassy phase in the wide temperature range below the onset temperature of the second exotherm peak. The presence of the glassy phase without appreciable precipitates even after the completion of the first exotherm peak has not been reported so far in spite of a large number of crystallization data on amorphous and glassy alloys. The precipitates at the temperatures just below the second exotherm peak for PHE Fe- and Zr-based glassy alloys are big cubic χ-FeCoNiCrMo(B) with a lattice parameter of about 0.90 nm and Zr2M (M = Al,Fe,Co,Ni,Ag) with a lattice parameter of about 1.2 nm, respectively. The precipitation of these metastable phases with large unit volumes needs long-range atomic rearrangements, but the atomic diffusivity in the PHE glassy alloys is very low, resulting in the formation of the clustered glassy phase. The clustered glassy alloys exhibit high strength and unprecedented plasticity for PHE Zr–Nb–Al–Ni–Cu BMGs, very high coercive force for Nd-Fe-Al BMGs, good soft magnetic properties in conjunction with better plasticity for PHE Fe–B–Si–P–Cu BMG and high thermal resistance to crystallization for PHE Zr–Al–Ni–Cu–Ag BMGs, and hence are expected to become important as a new type of engineering glassy material.