Achievement of sub-nanometer surface roughness of bearing steel via chemical mechanical polishing with the synergistic effect of heterocyclic compounds containing N and S

An ultra-smooth surface is required for mechanical components to improve the lubrication performance. In this study, the combination of 5-methyl-1H-benzotriazole (5-methyl-BTA) and thiazole (TA) was used as an effective composite corrosion inhibitor for chemical mechanical polishing of GCr15 bearing steel. The results reveal that, compared with the single corrosion inhibitor 5-methyl-BTA or TA, their combination results in lower surface roughness. By the synergistic corrosion inhibition effect of 5-methyl-BTA and TA, an ultra-smooth GCr15 steel surface with a sub-nanometer surface roughness Ra is achieved and the underneath substrate is free of damage. Specifically, 5-methyl-BTA can be first rapidly adsorbed on the GCr15 steel surface through the chemical and physical pathways. Then TA can be physically adsorbed on the GCr15 steel surface, and in addition, a part of TA may be further physically adsorbed on the outer layer of the surface film. As a result, the effective corrosion inhibition film is formed and cooperates with the oxide film to suppress the corrosive wear. Through our developed two-step polishing method, a rough GCr15 steel surface with the Ra of 263 nm can become ultra-smooth with the Ra of 0.8 nm in 21 min, providing a promising ultra-precision processing technique for industry.