Tribo-Mechanical and Electrochemical Properties of Carbonitrided 316 Austenitic Stainless Steel by rf Plasma for Biomedical Applications

AISI 316 austenitic stainless steel was carbonitrided using rf plasma with purpose of using low-cost orthopedic implant materials in biomedical applications besides the manufacturing requests. The plasma treatment process was accomplished at low working gas pressure of 0.075 mbar in nitrogen-acetylene gaseous mixture. The plasma-processing time was fixed at 10 min while the plasma-processing power was varied from 450 to 650 watt. The effect of plasma treatment power on the structure, tribological, mechanical, electrochemical and biocompatibility of AISI 316 has been investigated. The structural results demonstrated the formation of nitrogen and carbon solid solutions, chromium nitride, iron carbide and iron nitride phases in the treated samples. The microhardness of the treated layer increases with increasing the processing power to reach a maximum value of approximately 1300 HV0.1 at 600 W which represents more than 6-folds increase in microhardness in comparison with the untreated matrix. The wear and corrosion resistance of the treated AISI 316 were enhanced compared to the untreated one. The friction coefficient was reduced from nearly 0.5 for the untreated substrate to nearly 0.3 for the carbonitrided sample. The surface energy and wettability of the carbonitrided samples were augmented as the plasma-processing power increased. Furthermore, the numbers of grown mesenchymal stem cells are higher for carbonitrided samples compared to the untreated one. The formation of nitrogen and carbon solid solution, chromium nitride, iron nitride and iron carbide hard phases after carbonitriding process is responsible for achieving good mechanical, tribological, biocompatibility and electrochemical properties for AISI 316 alloys.