Enhanced microhardness in Zr65.0Al7.5Ni10.0Cu17.5 amorphous rods on coprecipitation of nanocrystallites through supersaturated intermediate solid phase particles

Abstract

Amorphous rods of 4 mm diameter of Zr_65.0Al_7.5Ni_10.0Cu_17.5 crystallize in a very fine microstructure, with an average size of the crystallites of 19 nm, on an isochronal heating over 655–860 K for a short period of 300 s. The multiple primary crystallization occurs with subsequent precipitation transformation of Zr‐rich supersaturated tetragonal Ni₁₁Zr₉‐ type (T phase) and cubic NiZr₂‐ type (I phase) phases to a thermally stable three phase mixture of α‐Zr (hexagonal), T and I phase finely dispersed one into another. It results in an enhanced microhardness of 6.9 GPa in the crystallized sample in comparison to 4.6 GPa in the amorphous sample, 5.7 GPa in the well‐crystallized bulk ingots, or 1.75 GPa or lower in the pure Zr or other elemental starting components. The results are discussed with the refined microstructure and the formalism of the local precipitations of α‐Zr nanocrystallites in the locally phase separated microscopic domains of related supersaturated intermediate phases.