Bulk metallic glasses (BMGs) exhibit exceptional properties, but are difficult to machine due to their high hardness and brittleness. In this study, we propose a novel hybrid machining strategy integrating cold plasma (CP) pretreatment with ultrasonic vibration-assisted micromilling (UVAM), termed CP-UVAM, to overcome these challenges. We reveal the fundamental mechanism by which CP independently optimizes machining: it transforms the BMG surface from hydrophobic to superhydrophilic (contact angle<10°) through oxidation and the introduction of polar groups, thereby enhancing lubricant penetration. Crucially, CP treatment increases the near-surface free volume, significantly improving plastic deformability, as evidenced by nanoindentation (15%–20% reduction in the first pop-in force) and nanoscratching tests. Four methods—conventional milling (CM), CP-assisted milling (CPAM), UVAM, and CP-UVAM—were systematically compared. While CPAM alone delivered the best surface finish and least tool wear, UVAM achieved a 29.02% cutting force reduction at the cost of severe tool edge chipping. The synergistic CP-UVAM approach retained the force reduction advantage of UVAM (34.36% reduction vs CM) while dramatically mitigating UVAM-induced tool damage, reducing edge chipping by 43.97%, and achieving superior surface consistency (a surface roughness of 2.601 µm in the stable state). This study demonstrates that CP independently enhances BMG machinability and works synergistically with UVAM, enabling high-precision micromilling of this challenging material through the combination of plasma-induced plasticity and wettability with ultrasonic vibration-assisted force reduction.
Li et al. (Tue,) studied this question.