Characteristics of Cobalt Chromium Alloy Surfaces Finished Using Magnetic Abrasive Finishing

Freeform surfaces, including the femoral components of knee prosthetics, present a significant challenge in manufacturing. The finishing process is often performed manually, leading to high variation in quality. This study proposes using Magnetic Abrasive Finishing (MAF) to finish the cobalt chromium (Co-Cr) alloy femoral components of knee prosthetics and varying the surface pattern to alter surface wettability, which influences the tribological properties of the surfaces. As a first step, flat workpieces of the same material were used in this paper. To obtain an understanding of the relationship between surface pattern and wettability, two sets of finishing conditions were developed to yield two different surface patterns while maintaining roughness values (2–5 nm Ra). One surface consists of long cutting marks exhibiting strong directionality, while the other consists of short, intermittent cutting marks. The surface with strong directionality resulted in an increased contact angle between the workpiece and de-ionized water (from 90.0°±1.5° to 93.8°±2.5°), thus a decrease in wettability. The other surface showed a decreased contact angle (from 98.7°±5.3° to 93.3°±3.7°), thus an increase in wettability. This study experimentally demonstrates the feasibility of MAF to alter surface pattern—and to potentially alter the wettability—while maintaining initial surface roughness at a nanometer scale.