A TEM study on the crystallization behavior of an yttrium-doped Zr-based bulk metallic glass

Transmission electron microscopy (TEM) is used to conduct the systematic study of the annealing induced crystallization, both continuously and isothermally, of a Zr-based metallic glass. Through detailed microstructure analysis, it is found that the crystallization of this metallic glass is initialized by a nano-scaled primary crystallization process with a tetragonal structured crystal (a = 0.96 nm and c = 2.82 nm) as the primary phase. A eutectic crystallization is followed afterwards with two types of crystalline phases as the crystallization products, one of which is determined to be a metastable orthorhombic phase (a = 0.69 nm, b = 0.75 nm and c = 0.74 nm). Upon annealing at a raised temperature or isothermal treatments, a solid state phase transformation takes place and the orthorhombic metastable phase transforms into two types of tetragonal crystalline phases. The whole crystallization process of this metallic glass is in turn realized, and the thermal stability and nano-crystallization mechanism are discussed based on the microstructure and thermal analyses.