科研之友
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摘要
Bulk metallic glass composites (BMGCs) have good combination of mechanical properties when compared with monolithic bulk metallic glasses (BMGs) and conventional crystalline alloys. However, with high strength, high hardness and metastable atomic structures, BMGCs are classified as difficult-to-cut materials, and how to process BMGCs is important before their engineering applications. In this work, die-sinking electrical discharge machining (EDM) of BMGCs was conducted, and compared with conventional industrial pure Zr (Zr702), under both rough and refined conditions. The EDM performance, including material removal rate (MRR), surface roughness, surface morphology, element variation, and crystallization, was investigated. The findings have shown that the peak current contributed most to the variation of MRR and surface roughness of BMGCs, followed by pulse-on time. BMGC workpiece material was more easily removed by sparking than Zr702 due to the relatively lower melting point and smaller thermal conductivity. During sparking, the melted BMGC workpiece material tends to have smaller viscosity and larger explosive forces, resulting in larger craters, corrugated ridges, and resultant higher surface roughness. Nevertheless, good surface quality with low surface roughness comparable to conventional Zr702 was also obtained for BMGCs under refined conditions. After EDM, the composite microstructure of BMGCs changed to amorphous matrix and ZrC/TiC carbides for ZrCu-based and TiCu-based BMGCs, respectively. The mechanisms for the change of atomic structures in BMGCs during die-sinking EDM were discussed, and the findings have shown that the carbonization effect can be reduced or even eliminated by optimizing the processing parameters. Finally, strategies for achieving better die-sinking EDM performance of BMGCs were proposed.
