Formation of crystalline phase in strip cast Zr-Ti-Cu-Ni-Be bulk amorphous alloy

Abstract

A feasibility study has been made to fabricate the Zr-base amorphous alloy strips by strip casting which can offer cooling rates of 10(2) - 10(3) K/s. Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 (at. %) alloy was cast into 2 mm thick strips at a speed of 4.2 m/min. It has been shown that the microstructure of the strip consists of a small volume fraction of the polygonal crystalline particles in amorphous matrix. TEM and AES analyses show that the polygonal crystalline particles have FCC structure (a = 1.185 nm) with the composition rich in Be and poor in Zr and Ti. Some of the polygonal crystalline particles appear to be nucleated from the relatively coarse primary amorphous particles. DSC analyses and simulated heat treatments of the alloy show that the polygonal crystalline particles form in the melt at high temperature prior to the contact of the undercooled melt with the roll of strip caster.