Low temperature plasma carbonitriding of ASTM F138 and ASTM F1586 biomedical stainless steels

Low temperature carbonitriding has been reported to improve the wear resistance of engineering grade AISI 316 through the formation of a hybrid S phase, but little or no research work has been applied to medical grade austenitic stainless steels. In this study, the aforementioned hybrid S phase has been successfully implemented in the surface of two medical grade austenitic stainless steels, ASTM F138 and ASTM F1586, as well as on engineering grade AISI 316 for comparison. The wear behaviour of the plasma carbonitrided and the untreated samples was compared using reciprocating sliding wear tests in air, Ringer's solution and distilled water. Experimental results have demonstrated that low temperature plasma carbonitriding can effectively reduce the wear of these two medical grade materials independent of the testing conditions. Wear results from the reciprocating wear test have shown that for the ASTM F138 alloy an improvement over the untreated material of 450% (in air) and 100% (in Ringer's solution) was registered; for the ASTM F1586 stainless steel, the improvements over the untreated materials were 380% (in air) and 40% (in Ringer's solution). It is proposed that the improved performance of the treated samples can be attributed to a desired combination of the significantly improved hardness which provides a better support to the surface oxide layer and the retained good corrosion resistance.