Investigation of surface characteristics on post processed additively manufactured biomaterial through magnetorheological fluid assisted finishing process

Abstract

Additive Manufacturing (AM) is recently used to manufacture biomedical implants as the customized fabrication of the desired complex shapes is easily achievable with reduced manufacturing time and material waste. However, the poor surface quality of additively manufactured products is a major concern over biomaterials' functionality. Magnetorheological Fluid Assisted Finishing (MFAF) process is an advanced surface finishing process used to improve the workpiece surface quality without altering surface topography. Selective Laser Melting (SLM) is utilized in the presented study to fabricate biomaterials using SS316L powder, and surface quality is further enhanced through the MFAF process. However, average surface roughness (Ra) only delivers the details regarding the average altitude of peaks and depth of valleys from the central line. Therefore, kurtosis (Rku) and skewness (Rsk) analysis of the polished surface are also carried out to determine detailed surface characteristics. The bio-tribology analysis of the polished surface of the AM implant determines its sustainability inside the human body. Hence, a wear test utilizing the pin-on-disc process is performed on the finished surface to determine the efficiency of the polishing process during tribological contact of the biomaterials with the bone. Further, the improved surface roughness parameters (Ra, Rku, and Rsk) after the MFAF of AM implant's surface are also investigated with an optical profilometer and scanning electron microscope. The MFAF process produced a highly polished surface on the biomaterial and a final Ra value of 32.46 nm is attained after polishing from its initial value of 8.32 μm with a decrease in wear rate (i.e., from 9.86 × 10−5 mm3/min to 0.46 × 10−5 mm3/min). The value of kurtosis less than three (i.e., 0.79) indicates that the flat peaks are generated on the surface irregularities after MFAF. Similarly, the negative skewness (i.e., Rsk = −0.28) represents that the number of peaks is less than the valleys. It indicates that the chances of wear out of the surface irregularities from the workpiece on their tribological contact are very low.