Atomic level surface of nickel superalloy induced by novel chemical mechanical polishing and its material removal mechanism elucidated by nanoscratching through molecular dynamics simulations

Nickel (Ni) superalloy is hard, and has the nature of corrosion and wear resistance. Therefore, it rises a challenge to achieve atomic level surface. To solve this challenge, novel chemical mechanical polishing (CMP) was developed on a self-made polisher. The CMP slurry contains silica and praseodymium oxide abrasives, hydrogen peroxide, glutamic acid, and sodium carbonate. After CMP, surface roughness Sa of 0.144 nm is garnered, and material removal rate is 118.3 nm/min. To the best of our knowledge, Sa is the lowest compared with previous reports hitherto. Material removal mechanisms are interpreted by nanoscratching performed through molecular dynamics (MD) simulations. Calculated surface roughness Sa by MD simulations increases from 0.121 to 0.272 nm with increasing nanoscratching depth from 5 to 20 Å. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy reveal that Ni superalloy was oxidized by hydrogen peroxide. Released metal ions dissolved by H + ions were chelated by glutamic acid, and chelating equations are proposed. The chelation of metal ions by glutamic acid occurs at amino and carboxyl groups, due to the change of stretching vibration frequency of N-H varied from 3111 to 3060 cm -1 , as well as symmetrical stretching frequence of C=O shifted from 1683 to 1641 cm -1 . Our findings provide new insights for Ni superalloy to acquire atomic level surface using CMP and its material removal mechanism unraveled by MD simulations via nanoscratching.