Plasma electrolytic polishing for improving the surface quality of zirconium-based bulk metallic glass

Zr-based bulk metallic glass (Zr-based BMG) biomedical parts are polished to produce the clinically desired surfaces. In view of this, the present work proposes an environmentally friendly flexible plasma electrolytic polishing (PeP) technique for processing the Zr52.5Cu17.9Ni14.6Al10Ti5 BMG. The stable polishing process and the postelectrochemical composition changes of the Zr-based BMG were investigated, and the surface smoothing mechanism was thus revealed. The roughness and gloss of the polished surface were evaluated to optimize the electrolyte composition ratios and other important process parameters. The crystallization degree and corrosion resistance of the polished surfaces were examined to ensure the applicability of PeP for biomedical Zr-based BMGs. The results showed that a high voltage of 300-380 V led to the development of a steady vapor gaseous envelope and plasma channels for Zr-based BMG polishing. It was noted that the preferential plasma discharge of the high parts (Zr elements) during PeP reacted with the fluoride salt electrolyte and formed a water-soluble zirconium fluoride (ZrF4). Moreover, by using an optimal electrolyte with 3% ammonium salt and 0.1% fluoride salt, the workpiece could be polished efficiently without crystallization. Overall, the surface roughness of the workpiece after the PEP was reduced by 8 times, while the gloss was increased by 10 times and the surface corrosion resistance was enhanced remarkably.

Automated summary

In this study, an environmentally friendly flexible plasma electrolytic polishing (PeP) technique was proposed for processing Zr-based BMG biomedical parts. By optimizing the electrolyte composition ratios and process parameters, the surface roughness of the workpiece was greatly reduced, the gloss was significantly increased, and the surface corrosion resistance was remarkably enhanced.