Atomic-Level Surface on Bearing Steel Produced by Environmentally Friendly Chemical Mechanical Polishing Using Silica and Ceria Hybrid Abrasives

Bearing steel is very hard and has the nature of wear resistance, making it a typically difficult-to-process alloy. In this regard, it is a challenge to achieve an atomic-level surface on bearing steel. To solve this challenge, we propose an environmentally friendly chemical mechanical polishing (CMP), and the CMP slurry contains silica and ceria hybrid abrasives, malic acid, hydrogen peroxide, and disodium ethylenediaminetetraacetate. After CMP, a surface roughness (Sa) of 0.162 nm is achieved, and the material removal rate is 249.5 nm/min. Transmission electron microscopy (TEM) reveals that the thickness of the damaged layer is 7.5 nm. To the best of our knowledge, both the Sa and the thickness of the damaged layer are the lowest for an atomic-level surface on bearing steel so far. Nanoscratching was carried out by molecular dynamics (MD) simulations. MD simulations confirm that when the cutting depth is 25 Å, the thickness of the damaged layer is about 7 nm, which is in good agreement with that of TEM measurements. They also indicate that the damaged layer suffer from local extrusion, plastic flow induced by shear, stress concentration, and dislocation proliferation. CMP mechanisms are unraveled by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). XPS shows that a chelation reaction happened due to the appearance of the O–C═O/C–O peak for Cr 2p at 288.7 and 288.3 eV after CMP and immersion in the slurry, respectively. The chelation reaction is also verified by O 1s through the emergence of C–O/COO – peak at 534.3 eV. FTIR further displays that the chelation reaction occurred after immersion in the CMP slurry because of the generation of vibrational peak of C–H at 2921 and 2849 cm –1, as well as the production of COOH peak at 1665 cm –1 . CMP mechanisms concluded that hydrogen peroxide oxidized the surface of bearing steel, forming oxides of iron and chromium. Then, Cr 3+ and Fe 3+ ions were released in H + environment derived from malic acid. The released ions were complexed by malic acid and disodium ethylenediaminetetraacetate. Our findings provide insights into fabricating an atomic-level surface on bearing steel using environmentally friendly CMP for a hard and wear-resistant alloy.