OS3-2-4 Non-destructive characterization of laser-peened materials with synchrotron radiation of SPring-8

Abstract

Laser peening without coating (LPwC) is an emerging surface technology to enhance fatigue strength and prevent stress corrosion cracking (SCC) of metallic materials. LPwC was applied to SUS304 austenitic stainless steel and AC4CH cast aluminum alloy samples with a Q-switched and frequencydoubled Nd:YAG laser. Residual stress depth profile over the top surface of the SUS304 sample was precisely measured by a constant penetration depth (CPD) method, which is in the framework of the sin^2Ψ method and can strictly control the X-ray penetration depth into the sample material. By combining the CPD method with high energy X-ray of SPring-8, the depth profile was evaluated non-destructively before, during and after heat treatment up to 673 K (400 ℃). The residual stress in the top surface of the SUS304 sample is entirely compressive despite the direct irradiation of intense laser pulses on the material and the thermal loading. High-cycle fatigue testing was performed for AC4CH samples with and without LPwC, which demonstrated that LPwC significantly prolonged the fatigue life. Replication technique was applied to evaluate the propagation behavior of fatigue cracks on surface. Three-dimensional (3D) images of fatigue cracks were reconstructed by micro tomography (μCT) with phase contrast effect using highly parallelized coherent X-ray of SPring-8. The retardation of crack growth was confirmed in the material with LPwC in the images of μCT.