High-temperature fatigue crack growth characteristics of IN718 Ni-based alloy treated by laser peening

The characteristics of fatigue crack growth (FCG) of laser peened IN718 Ni-based alloy at high temperature with different laser power densities were studied. The residual stress relaxation and micro-structure evolution of the samples at high temperature after laser peening (LP) were analyzed by X-ray diffraction technique and scanning electron microscopy (SEM), respectively. Meanwhile, SEM was used to characterize the fracture morphologies of the samples. The strengthening mechanism of LP on the high-temperature FCG resistance of IN718 Ni-based alloy was discussed. The results showed that large compressive residual stress, fine grains and complex grain boundaries induced by LP could significantly enhance the resistance of FCG at 700 degrees C. As a result, the FCG rate was decreased and fatigue life of the sample was increased. In addition, the laser power density was found to be inversely proportional to the average spacing of fatigue striations and directly proportional to the size and depth of dimples, which indicated that the increase in laser power density can improve the high-temperature FCG resistance of IN718 Nibased alloy.