Close-to-Atomic Precision Surface Achieved through a Neutral and Eco-friendly Slurry in Chemical Mechanical Polishing of TC4 Alloy

Abstract

Atomic and close-to-atomic scale manufacturing represents a leading-edge method for improving the operational performance of titanium alloy components within the aerospace, biomedical, and new energy fields. Regrettably, despite chemical mechanical polishing (CMP) being presently one of the most efficient techniques for achieving atomic layer polishing, the absence of a neutral and environmentally sustainable slurry capable of producing ultrasmooth and low-damage surfaces in titanium alloy CMP is notable. In this study, a neutral and eco-friendly slurry composed of H₂O₂ and alkali metal ions is proposed, which is different from the traditional TC4 alloy polishing where H⁺, OH^–, or hazardous chemicals require deep involvement. The results demonstrate that the decreasing dynamic ionic radius of alkali metal ions significantly promotes the interfacial mechanochemical reactions. Therefore, an ultrasmooth surface with close-to-atomic precision (S_a ≤ 1 nm) can be achieved by adding only 150 mmol/L K₂SO₄ and 10 wt % H₂O₂. The presence of H₂O₂ predominantly affects the electrochemical behavior, contributing to enhanced chemical corrosion. K₂SO₄ causes the effective thickness of the electrical double layer to decrease to 0.56 nm. The thinner electrical double layer can amplify the action of chemical corrosion and mechanical wear. They synergistically contribute to the equilibration of mechanochemical reactions at the sliding interface. The novel slurry is highly desirable for both the environment and people as well as for Ti alloy CMP industries.