Evaluation of microstructural evolution during torsion fatigue and surface performance of high nitrogen stainless steels suitable for biomedical applications

Abstract

In this contribution the microstructural changes of four different solution annealed face centered cubic/FCC materials subjected to torsion fatigue were studied. Standard materials X5CrNiMo17‐13‐2 (1.4441, AISI 316 L) and the Co‐base alloy CoCr29Mo6 in addition to two high‐nitrogen stainless steels X13CrMnMoN18‐14‐3 (1.4452) and X6CrNiMnMoN22‐10‐4‐3 were investigated. The torsional fatigue tests were carried out by means of stress controlled incremental step tests at 25 Hz and 3 Hz, respectively. Simultaneously the shear strains were measured in order to gain stress‐strain hysteresis at every 30th cycles. The solution annealed X13CrMnMoN18‐14‐3 (1.4452) and X6CrNiMnMoN22‐10‐4‐3 nitrogen containing steels as well as 316 L‐type stainless steels have been tested and their fatigue endurance limits were determined and compared to that of the CoCr alloy. Transmission electron microscope observations were carried out for the investigated materials before and after the fatigue tests. The results of Transmission electron microscope observations reveal the effect of further nitrogen additions on the fatigue properties. Microstructure observations depicted the effect of nitrogen additions on the modification of slip behavior and the role of the stacking fault energy herein. Wear tests for alloys with substantially more nitrogen than can be accommodated interstitially, form coarse CrN precipitates. These precipitates significantly influence the abrasive wear characteristics of the alloy, particularly when they are large (i. e., 50 μm in width).