Nucleation, growth, and glass formation in an electron-beam surface-processed Cu47Zr53 alloy

Abstract

A Cu47Zr53 alloy was surface processed with a directed-energy electron beam. Optical microscopy, x-ray diffraction, and transmission electron microscopy were used to identify the resolidified phases obtained under systematically varied rapid solidification conditions. The results of the investigation indicate that the underlying bulk substrate always nucleates the growth of a crystalline phase that was identified as a metastable CuZr phase with an ordered bcc (B2) structure. The maximum growth velocity of this phase was determined to be between 0.05 ± 0.02 m/s. This limit was compared under different assumptions to the predictions of a reaction rate growth theory. As the solidification speed increased beyond this limit, the crystalline growth eventually ceased and glass formation occurred in the remaining undercooled liquid under rapid cooling conditions. Crystalline particles also nucleated and grew in the liquid at intermediate cooling rates. These particles had a dendritic morphology and were also a CuZr phase with the B 2 structure.