Characterization of wear resistance and corrosion during magnetorheological fluid assisted finishing (MFAF) of Ti-6Al-4V and duplex stainless steel for enhanced biocompatibility

Abstract

The sustainability of biomaterials relies on their interaction with the proteins, fluid, and cells present inside the human body. The biomaterials’ enhanced surface roughness parameters and mechanical properties (i.e. wear resistance) are responsible for reducing degradation (i.e. corrosion rate) to enhance life span during musculoskeletal interaction. The present study compares the biocompatibility between two biomaterials (i.e. Ti-6Al-4V and DSS) polished through the Magnetorheological Fluid Assisted Finishing (MFAF) process. MFAF process can produce nano-level average surface roughness (R_a) and is used to improve the quality of the biomaterial's surface. However, apart from R_a, two other surface roughness parameters, namely skewness (R_sk) and kurtosis (R_ku) analyze the characteristics of the irregularities formed on the polished surface. During the MFAF process, Trochoidal, a high-speed surface finishing toolpath, is used to map the workspace on the Duplex Stainless Steel (DSS) and Ti alloy (Ti-6Al-4V) biomaterials to enhance their biocompatibility with a reduced finishing time. However, during the pin-on-disc wear tests, an Ultra High Molecular Weight Polyethylene (UHMWPE) is used as the disc to imitate the interface of the bone with the implants for analyzing wear resistance. During experimentation, it is observed that the wear resistance of DSS and Ti-6Al-4V is improved to 3.19 × 10⁻⁶ and 0.123 × 10⁻⁵ mm³/min from its initial value of 7.65 × 10⁻⁶ and 2.68 × 10⁻⁵ mm³/min, respectively. Furthermore, the dependency of initial surface roughness parameters over the wear resistance of the biomaterials is also analyzed. A three-electrode-based electrochemical test with 0.5 M NaCl concentration is utilized to replicate the human body fluid while analyzing the corrosion resistance of the biomaterials. It is observed that the MFAF process enhances the corrosion resistance of the DSS and Ti-6Al-4V to 0.0037 and 0.0114 mm/year, from its initial values of 0.0079 and 0.0130 mm/year, respectively.