Comparative Study on Wear Behavior, Corrosion Resistance, and Bioactivity Performance of Conventional and nTopology-Designed DMLS Co-Cr Alloys for Biomedical Implant Applications

Objectives: To make a comparative study on the wear behavior, corrosion resistance, and bioactivity performance of conventional Co-Cr (Cobalt-Chromium) alloy and nTopology-designed Co-Cr alloy sintered by Direct Metal Laser for biomedical implant applications. Method: Comparative investigations were made on the CM-CoCr (Conventional Co-Cr) alloy and NT-DMLS-CoCr (nTopology-designed DMLS Co-Cr) alloy specimens. By using pin-on-disc tribometer wear tests were performed under 10, 30, and 50 N loads at a sliding velocity and a sliding distance of 1.25 m/s and 1000 m respectively. Corrosion behavior was also evaluated with the help of potentiodynamic polarization test in simulated body fluid (SBF) at 37ºC. Bioactivity behavior was assessed by immersing the specimens in SBF for a duration of up to 28 days and monitoring the apatite formation. Here CM-CoCr was chosen as the control material for comparison. Findings: The NT-DMLS-CoCr specimens exhibited better tribological, electrochemical, and bioactive performance when compared with CM-CoCr. At 50 N, the wear rate decreased from 6.24 × 10-5 mm3/Nm for CM-CoCr to 3.46 × 10-5 mm³/Nm for NT-DMLS-CoCr, representing a reduction of approximately 44.5%. The friction coefficient also gets decreased from 0.55 to 0.43. Potentiodynamic polarization studies concluded that the corrosion current density gets decreased from 1.76 μA/cm2 to 0.42 μA/cm2, while the corrosion rate gets reduced from 0.017 mm/year to 0.004 mm/year. Bioactivity evaluation revealed enhanced apatite formation, with NT-DMLS-CoCr achieving apatite coverage of 95% after 28 days compared to that of 68% for CM-CoCr. The enhanced performance is attributed in the refined DMLS microstructure and interconnected gyroid lattice architecture, which improved load distribution, passive film stability, and biomineralization behavior. Novelty: This study presents a comparative evaluation of conventional and nTopology-designed DMLS Co-Cr alloys, exhibiting the advantages of lattice-engineered additive manufacturing best suited for biomedical implant applications. Keywords: Co-Cr, nTopology, DMLS, Biomedical applications