Effects of Size and Volume Fraction of Precipitated Crystalline Phase Induced by Friction Stir Processing on Hardness in Zr–Al–Ni–Cu Bulk Metallic Glass

Abstract

The effects of the size and volume fraction of the precipitated crystalline phase induced by friction stir processing (FSP) on the hardness in Zr–Al–Ni–Cu bulk metallic glass (BMG) was examined. The microstructure in the friction zone (FZ) exhibits an amorphous “band-like” structure with a small number of nanoscale crystalline particles. On the other hand, the microstructure in the FZ near the finishing point of the process exhibits a large number of nanocrystalline particles with a size of less than 20 nm and amorphous phase. The difference in the microstructures of FSP regions is explained in terms of differences in the heat input by FSP. The hardness in both FSP regions is greater than that of heat-treated specimens with almost the same volume fraction of the crystallized phase. Control of the size and volume fraction of precipitated crystalline phase induced by FSP offers the possibility of further improvement in the mechanical properties of BMGs.