Exploring the role of --NH₂ functional groups of ethylenediamine in chemical mechanical polishing of GCr15 bearing steel

Ethylenediamine with two -NH₂ functional groups was used as a critical complexing agent in chemical mechanical polishing (CMP) slurries for a high carbon chromium GCr15 bearing steel (equivalent to AISI 52100). The polishing performance and corresponding mechanism of -NH₂ functional groups were thoroughly investigated as a function of pH. It is revealed that, when polished with ethylenediamine and H₂O₂-based slurries, the material removal rate (MRR) and surface roughness R_a of GCr15 steel gradually decrease as pH increases. Compared with acidic pH of 4.0, at alkaline pH of 10.0, the surface film of GCr15 steel has much higher corrosion resistance and wear resistance, and thus the material removal caused by the pure corrosion and corrosion-enhanced wear are greatly inhibited, resulting in much lower MRR and R_a. Moreover, it is confirmed that a more protective composite film, consisting of more Fe³⁺ hydroxides/oxyhydroxides and complex compounds with -NH₂ functional groups of ethylenediamine, can be formed at pH of 10.0. Additionally, the polishing performance of pure iron and a medium carbon 45 steel exhibits a similar trend as GCr15 steel. The findings suggest that acidic pH could be feasible for amine groups-based complexing agents to achieve efficient CMP of iron-based metals.