Improvement of fretting fatigue strength of stainless steel by hybrid surface treatment composed of plasma nitriding and fine-particle bombarding

Abstract

This study was conducted to improve fretting fatigue strength of austenitic stainless steel JIS SUS316 by the hybrid surface treatment composed of plasma nitriding (hereafter, PN) and fine-particle bombarding (FPB). In the study, finite element analysis (FEA) was also performed to investigate local stress-strain response induced at the contact edges in fatigue specimens. Since the above hybrid surface treatment didn't affect the microstructure in the substrate, there was no influence on the mechanical properties. Fretting fatigue strength was markedly improved by the hybrid surface treatment, and its improvement percentage reached 50%. The results of FEA showed that "shakedown" occurred at the contact edges under applied cyclic stress so that local mean stress there became zero. The formed hardened layer had no effect to improve wear condition at the contact edges. Accordingly, it was suggested that the improvement of fretting fatigue strength resulted from the increase in crystallographic slip resistance by the formed hardened layer.