Atomic surface of titanium alloy using novel chemical mechanical polishing with rare earth composite abrasives

Titanium (Ti) alloy is a typical difficult-to-process material, rising a challenge to obtain atomic surface for chemical mechanical polishing (CMP). Furthermore, toxic and polluted slurries are usually applied to CMP, resulting in the potential threat to the environment. To solve these items, novel green CMP was developed for a Ti alloy, containing lanthanum‑cerium oxyfluoride, silica, citric acid, hydrogen peroxide, glycine and deionized water. After CMP, atomic surface with surface roughness Sa of 0.155 nm is achieved, at a measurement area of 50 × 50 μm², and the material removal rate (MRR) is 20.16 μm/h. To the best of our knowledge, for an atomic surface, the surface roughness and MRR are both the best for a Ti alloy. CMP mechanisms are elucidated by electrochemical measurements, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Firstly, Ti alloy was oxidized by hydrogen peroxide, generating oxides of Ti and aluminum (Al). The oxides were dissolved by hydrogen ions derived from citric acid. Ti and Al ions were chelated with hydrogen peroxide and citric acid, respectively. Chelation formulas were suggested between Al ions and citric acid. Finally, the soft oxidized layer on the surface of Ti alloy was removed by abrasives and a polishing pad. The developed green CMP proposes new insights to achieve atomic surface on a Ti alloy with a high MRR, providing a novel method to polishing difficult-to-process material.