A Hybrid Electrochemical Magnetorheological Finishing Process for Surface Enhancement of Biomedical Implants

Abstract The proposed novel polishing method, hybrid electrochemical magnetorheological (H-ECMR) finishing, combines electrochemical reactions and mechanical abrasion on the workpiece surface to reduce finishing time. Moreover, H-ECMR finishing on the biomaterial surface produces a uniform, thick passive oxide layer to improve corrosion resistance. Herein, the electrolytic solution facilitates the chemical reaction and acts as a carrier medium for carbonyl iron particles (CIPs) in magnetorheological (MR) fluid. The synergic action of the two processes reduces the surface finishing time, which takes longer in the case of the conventional magnetorheological Finishing (MRF) process, as observed experimentally. The developed H-ECMR finishing process employs an electromagnet, maneuvering in situ surface quality variation by altering the magnetic field during finishing. The magnetic shield material (i.e., mu-metal) confines the bottom of the electromagnet core to restrict the magnetic field's leakage and provide a uniform and concentrated magnetic field at the polishing spot. The effectiveness of the H-ECMR process is evaluated based on various surface roughness parameters (i.e., average surface roughness (Ra), skewness (Rsk), and kurtosis (Rku)) and compared with the MRF process. A 96.4% reduction in Ra value is attained in the H-ECMR polishing compared to 49.6% in MRF for identical polishing time. Furthermore, an analytical model is developed to evaluate the final Ra attained from the developed H-ECMR polishing process and agrees well with the experimental results. The impact of different process parameters on surface roughness values is also analyzed. The electrochemical reaction forms a thick and unvarying passive layer on the Ti–6Al–4V surface as layer thickness increases to 78 nm from 8 nm. A case study on the femoral head of the Total Hip Arthroplasty (THA) for enhancement in the surface roughness and biocompatibility is performed through the developed H-ECMR polishing. The Ra value is decreased to 21.3 nm from 326 nm on the femoral head surface through the contour-parallel radial toolpath strategy.