Preliminary study on plasma surface modification of medical grade 316LVM and high nitrogen austenitic stainless steels

Specimens of 316LVM (F138) and high N (F1586) medical grade austenitic stainless steels ( ASS) have been low temperature plasma surface alloyed with nitrogen and carbon, at temperatures between 370-550 degrees C, to enhance their tribological properties and corrosion resistance. Systematic materials characterisation was conducted to investigate the microstructure, phase constituents, composition and surface mechanical properties of the plasma alloyed layers. The tribological and corrosion properties of the surface engineered materials have been evaluated by pin on disc tribometer and electrochemical corrosion tests. Experimental results showed that the surface hardness of both materials was significantly improved by all plasma treatments. Wear resistance was increased by up to 109 times, and wear volumes differed only slightly between treatments. Wear modes were altered from severe abrasive wear to mild oxidative wear. Anodic polarisation test results revealed that when nitrided at <= 400 degrees C and carburised at <= 450 degrees C corrosion properties are maintained or improved. Therefore, it is feasible to achieve combined improvements in wear and corrosion resistance for medical grade austenitic stainless, which has a great potential for the production of cost effective, long life ASS joint prostheses.