Evaluation of thickness variation of recast layer formation on nitinol from electrical discharge coatings process

Nitinol is an intermetallic alloy with outstanding properties that suitable as biomaterial. This alloy is capable of recovering to its initial shape after external loading through transformation of the crystalline structure. Unfortunately, excessive exposure of nickel element from this alloy is harmful to human body if released. Thus in this study, the alloy surface was deposited with an oxide layer via electrical discharge coating (EDC) process. The process was performed in deionized water and pure titanium as the electrode. The variation thickness of the recast layer formation was examined by analysing the effects of polarity, gap voltage and erosion depth. Single crater images and electrical waveforms were captured and utilised to elucidate the aforementioned effects. The results exhibited a significant change of layer thickness variation due to different polarity conditions. It was also confirmed that the single crater formation at different polarity was influenced by discharge energy. On other hand, the increase in the open gap voltage can expand the recast layer thickness in lower variation of reverse polarity condition. Finally, erosion depth attributed to a constant layer thickness but in low thickness variation when reverse polarity was employed.