The effect of laser shock processing on mechanical properties of an advanced powder material depending on different ablative coatings and confinement medias

Abstract

Based on the effect of confinement media and ablative coating, laser shock processing (LSP) is a surface modification processing with properties of high efficiency, cleaning, and non-pollution. At room temperature, water is used as the common confinement media and black tape is used as ablative coating in LSP. However, due to the instability of water and black tape at high temperature, warm laser shock processing (WLSP) favors silicone oil as confinement media and aluminum foil as ablative coating, where aluminum foil is pasted on specimen surface by thin vacuum grease. Due to the differences in confinement media and ablative coating, this work focuses on the effect of confinement media and ablative coating on surface quality and mechanical property of FGH98 powder material treated by LSP. FGH98 specimens were strengthened by LSP at room temperature with different confinement medias and ablative coatings. Three groups were divided based on confinement media and ablative coating: water+black tape, water+aluminum foil, and silicone oil+aluminum foil. The group of black tape and silicone oil was removed for the absence of practical significance in engineering. 2D and 3D surface topography was observed by white-light interference surface profilometer (WLI). In addition, surface microhardness and compressive residual stress were determined. The results show that a circular pit is induced by LSP, and its shape is similar to the shape of the Gaussian curve. Compared with the other groups, the 2D surface topography of the circular pit section in the silicone oil+aluminum foil group is smoother, which would delay crack initiation. After LSP treatment, surface microhardness is improved by 7.8-10.6%, and compressive residual stress raises from 355MPa to 896MPa in the first group. According to the comparison of residual stress and surface quality, the effect of confinement media and ablative coating groups on laser shock pressure is ranked in order: water+black tape > water+aluminum foil > silicone oil+aluminum foil. The main reasons for that group order are that shock pressure may be consumed by grease cream and the reduced acoustic impedance of silicone oil is lower than that of water.