Effect of cryogenic thermal cycling on the microstructure and mechanical properties of Zr-based bulk metallic glasses

This article investigates the effects of cryogenic thermal cycling (CTC) on the microstructure and plasticity of Zr60Cu20Al10Ni10 (Zr60) bulk metallic glass (BMG). The microstructure and mechanical properties of Zr60 BMGs at different energy states are assessed through room-temperature compression and nanoindentation tests. The heterogeneity of the internal structure of the CTC-treated samples causes a different response to thermal expansion resulting in a non-uniform local stress field distribution, which increases the energy state of Zr60 BMGs. At the same time, in the CTC-treated Zr60 BMGs, more free volume (or flow defects) is introduced, and the plasticity is increased. It has been found that, after CTC, the room-temperature plasticity of Zr-based BMGs can be significantly improved by 2-3 times compared to that of the as-cast samples. This introduces flow defects and the inhomogeneous distribution of the strain field causes the serration behavior during the deformation of BMGs to occur more frequently and the second peak of the relaxation spectrum to be more pronounced. This phenomenon indicates a more frequent generation of shear transition zones and shear band movement within them.