Effects of pH and H2O2 on the chemical mechanical polishing of titanium alloys

Titanium alloys have been widely used in many high-end components and parts in various fields, and the excellent surface quality of titanium alloys is highly required. In this study, chemical mechanical polishing (CMP) was used as an effective surface processing technology, and the effects of pH and H2O2 on the CMP performance of titanium alloys TA2 (pure titanium) and TC4 (Ti-6Al-4 V) were thoroughly investigated. It is shown experimentally that TA2 and TC4 perform the similar CMP performance as a function of either pH or H2O2. As pH increases from 4 to 10, the material removal rate (MRR) decreases while the surface roughness Ra increases; At pH 4, as the H2O2 concentration increases, the MRR first rapidly increases, reaches the summit at approximately 0.05 wt% H2O2, and then gradually decreases, while the Ra first decreases and then slightly increases. An optimal polishing performance can be achieved at 0.05 wt% H2O2 and pH 4. By characterizing the surface films of TA2, it is revealed that an oxide film with 3-4 nm thickness is formed after polishing, and the crystal structure of the underneath substrate remains complete without damage. The oxide film consists of two layers. The H2O2dependent CMP performance can be attributed to the change of the outer oxide layer. Specifically, by adding 0.05 wt% H2O2, the oxide film can be rapidly formed, matching with the abrasion, and the outer oxide layer becomes compact, and thus the MRR increases and the Ra decreases. The findings can provide a feasible CMP process for titanium alloys to achieve a satisfactory polishing performance.