Effect of Stress Frequency and Chemical Medium on the Corrosion-Fatigue Behaviour of 316L Stainless Steel

Among most used materials in implantology and the manufacture of surgical instruments, one finds the austenitic stainless steel AISI 316L, considered for its well adapted mechanical characteristics, its biocompatibility and in particular its resistance to uniform corrosion. The implants are often subjected to cyclic mechanical loads during normal activity of the human body, but they can also be attacked chemically by the physiological medium, under certain conditions. Between several mechanical and chemical parameters that can influence the corrosion-fatigue behavior of such material, the load frequency parameter is highlighted in this work. The aim is to determinate the effect of load frequency changes on the crack growth rate in corrosion-fatigue and to compare this effect in pure fatigue. To make experimental evidences, notched austenitic steel specimens have been submitted to cyclic bending tests inside a chlorine solution simulating the physiological medium (NaCl 0.9%). The bending stress value was taken equal to 200 MPa with a stress ratio R of 0, at different stress frequency values, respectively of 0.5, 1 and 2 Hz. When immersed in the chemical medium, the mechanical behavior of the steel sheets appears to be worst as the frequency decreases, as long as the crack size remains less than the critical one. In pure fatigue, the mechanical behavior changes with the increase of frequency and becomes detrimental. This corroborates different author works for such material.