Performance improvement of magnetorheological finishing using chemical etchant and diamond-graphene based magnetic abrasives

Thermally sprayed tungsten carbide coating is extensively engaged in wear resistance applications due to its good tribological properties. For some applications in aerospace, automotive, printing and forming industries, these coated components require a nanolevel surface finish. In the current investigation, magnetorheological fluid based finishing (MRF) process is carried out on the pre-polished tungsten carbide coating using standard magnetorheological (MR) fluid which contains diamond powder as the abrasive particles. In this case, the lower gripping strength of non-magnetic abrasives into the chain structures of carbonyl iron particles (CIPs) is responsible for inadequate material removal rate (MRR) and irregular polishing. To overcome these problems, MRF is conducted with a chemical etchant and that leads to a higher finishing rate due to the integrated effect of etching and polishing. However, it is perceived that the ability of normal MRF technique and MRF with chemical etchant is somehow restricted at a higher wheel velocity. To address these challenges of MRF process, CIP-diamond and CIP-diamond-graphene composite abrasives are introduced in this investigation. Due to the resilient attraction force among the composite abrasives, a much higher yield stress is observed and that leads to higher MRR and less spilling of MR fluid even at an elevated wheel speed. Composite magnetic abrasives are characterized using nanohardness tester, magnetometer and rheometer to assess its mechanical and magnetic behaviours. The lowest surface roughness (Sa) of 55 nm and highest MRR are attained using MRF with CIP-diamond-graphene abrasives.