Microstructural changes of Zr-based metallic glass during micro-electrical discharge machining and grinding by a sintered diamond tool

Micro-electrical discharge machining (micro-EDM) and grinding of Zr-based metallic glass (MG) were performed by using sintered polycrystalline diamond (PCD) as a hybrid tool. The microstructural changes of the workpiece surface layer were investigated. X-ray diffraction (XRD) patterns indicated that the ZrC phase and a few other unknown crystalline phases existed in the surface layer after micro-EDM. After shallow grinding, other new crystalline phases were detected on the surfaces. After deep grinding, however, the crystalline phases disappeared and an amorphous surface was obtained, the XRD and micro-Raman characteristics of which were similar to those of the as-cast MG surface. These results suggested that crystallization of MG in micro-EDM was hierarchical along the depth direction with different mechanisms. The results of surface morphology showed that grinding after micro-EDM not only effectively removed the crystallization layers to obtain an amorphous MG surface, but also improved the surface quality. The hybrid process provides a promising method to create three-dimensional micro features on a MG surface.