Synergistic Effect of F- and Persulfate in Efficient Titanium Alloy Chemical Mechanical Polishing

Titanium alloys require excellent surface quality to achieve superior performance in biomedicine. In this paper, chemical mechanical polishing (CMP) was employed to prepare a satisfactory TC4 alloy surface. F- and persulfate were used as critical additives to improve the CMP efficiency. In comparison with the basic slurry without F- and persulfate, the slurry containing only F-, and the slurry containing only persulfate, the slurries containing both F- and persulfate lead to a noticeable increase in the material removal rate (MRR), which is attributed to the synergistic effect of F- and persulfate. After adding 80 mM NaF and 100 mM (NH4)2S2O8 to the basic slurry, the MRR increases significantly from 11 nm/min to 203 nm/min, and the surface roughness Ra reaches 3.4 nm. Moreover, there is no processing damage in the substrate. For the synergistic effect, Ti in TC4 alloy is first oxidized to Ti3+ and Ti4+ oxides by persulfate, and then HF, F- and HF2- attack the oxides to produce soluble complex compounds, promoting the corrosion and the resultant MRR. This study provides a feasible way to achieve the high-efficiency CMP of titanium alloys via the synergistic effect of complexing agent and oxidizer to enhance the corrosive wear.