Attaining Ultra-Smooth 18CrNiMo7-6 Case Hardening Steel Surfaces with Chemical Mechanical Polishing

Abstract

Smooth surfaces are conducive to improving the lubrication of gears in mechanical systems. In this study, chemical mechanical polishing (CMP) was used to process 18CrNiMo7-6 case hardening steel, a typical material for gears. The results reveal that compared with formic acid and oxalic acid, citric acid can be used as a suitable complexing agent without causing apparent corrosion, probably due to the fact of its relatively stable adsorption. A synergistic effect exists between citric acid and H2O2. At pH 3, with 0.067 M citric acid and 1 wt% H2O2, a satisfactory CMP performance (i.e., a 514 nm/min material removal rate (MRR) and a 0.85 nm surface roughness Sa) was achieved. After polishing, no observable defects were found on the surface, and no discernible processing damage occurred to the substrate. In terms of the CMP’s mechanism, iron is first oxidized to Fe2+ and Fe3+, which then react with citric acid to form complexes. On the one hand, most of the complexes may stay on the surface to prevent further corrosion and, thus, the surface quality is excellent. On the other hand, the complexes may reduce the surface integrity and, thus, the MRR is high. The findings open new avenues for attaining ultra-smooth steel surfaces with CMP through controlling corrosive wear.

Enhancing Chemical Mechanical Polishing Efficiency of Steel with Sulfate

“…Figure 5 shows the FTIR results. Considering the surface film is very thin and only several nanometers, 12,28 but the FTIR measuring depth is about micrometers, 29 the signal can be relatively weak. Here we used the FTIR data to analyze the trend qualitatively.…”

“…6 In recent years, our research group has extendedly applied CMP to process steels. [7][8][9][10][11][12] Jiang et al 8 investigated the effects of pH, the complexing agents such as glycine, H 2 O 2 , and benzotriazole (BTA) on the CMP performance of AISI 52100 steel (equivalent to GCr15 steel). With the slurry containing 4.0 wt% colloidal silica, 0.1 M glycine, 1.0 wt% H 2 O 2 , 10 mM BTA and at pH 4.0, the surface roughness R a could reach 1.8 nm.…”

“…However, the material removal rate (MRR) seems low, only about 40 nm min −1 . For the CMP of 18CrNiMo7-6 steel, Peng et al 12 tried carboxylic acids as the complexing agents. It was found that citric acid could be a proper complexing agent because it could be stably adsorbed on the steel surface and weaken the surface during CMP.…”