Effects of laser shock peening on Inconel 738LC to improve mechanical and fatigue characteristics

Abstract

The effectiveness of laser shock peening at both room and elevated temperatures was examined for Inconel 738 low-carbon, a material widely used for gas turbine blades. Laser shock peening was performed with a Nd:YAG laser (wavelength = 532 nm, pulse duration = 8 ns, repetition rate = 10 Hz, top-hat profile) using aluminum foil (100 μm thick) as the protective coating at a laser intensity of 10 GW/cm2 and pass number of 10. As a result of laser shock peening, the surface hardness increased by 38%, and the compressive residual stress increased by approximately eleven times compared with that of the unpeened samples. A low cycle fatigue test was performed at room temperature and elevated temperature (850 °C) under strain control. At room temperature, the fatigue life of laser shock-peened samples increased by approximately 2.4 times that of the unpeened samples. At the high temperature of 850 °C, the fatigue life of the laser shock peened samples was overall similar to that of the unpeened samples, either slightly higher or lower depending on the applied total stress level. The results showed that laser shock peening is beneficial for enhancing fatigue strength at low temperatures, but its effectiveness largely disappears at a temperature as high as 850 °C, possibly owing to severe thermal relaxation.