Effect of different galvanic coupling methods on the surface chemical transformation of TC4 titanium alloy

Abstract

In clinical applications, titanium and its alloy implants often suffer from corrosion, wear and tear, and poor biological activity. Surface modification is critical for improving the stability and bioactivity of titanium and its alloys. Zinc phosphate chemical conversion has received increasing attention as a promising technique for biomedical applications. However, the presence of a passive oxide layer on the TC4 (Ti6Al4V) surface poses challenges for conventional chemical conversion methods. In this study, the principle of galvanic coupling was utilized to facilitate the surface chemical transformation of TC4 titanium alloy, referred to as galvanic coupling phosphate chemical conversion (GCPCC). The effects of two types of galvanic coupling and different plastic deformations on the surface chemical transformation of TC4 titanium alloy at different temperatures were mainly investigated. The results indicate that the Ti/Fe multipoint coupling formed by magnetron sputtering during chemical transformation at 70 °C significantly enhances the nucleation sites of hopeite (Zn3(PO4)2·4H2O) and accelerates the nucleation rate. Compared with line-coupled conversion coatings, multipoint coupling GCPCC coatings exhibit superior uniformity and finer microstructure, and the thickness of the laths is significantly reduced from 5 to 10 μm to less than 1 μm. Moreover, the temperature exerts a substantial influence on the formation of conversion coatings. At 70 °C, the GCPCC coating primarily comprises hopeite, while the coating resulting from chemical conversion treatment consists of both hopeite and an amorphous ZnP-like granular coating at 50 °C.