Experiment Study on Improving Fatigue Strength of K24 Nickel Based Alloy by Laser Shock Processing without Coating

Laser shock processing without coating (LSPwC) was used to improve the fatigue resistance of K24 nickel based alloy. Firstly, high cycle vibration fatigue experiment was adopted to verify the LSPwC strengthening effect. Compared to the untreated samples, the results of the vibration fatigue experiments show that the fatigue strength of K24 alloy is enhanced and improved from 282 MPa to 328 MPa after LSPwC. Secondly, the effects of multiple impacts on mechanical properties and fatigue fracture morphologies were investigated, which were observed and measured by scan electron microscope (SEM), X-ray diffractometer and microhardness tester. The results indicate that the residual stress presents compressive state on the superficial layer with about 150 μm depth and the maximum value reaches -595 MPa. The microhardness (HV_0.5) is about 5260 MPa with about 100 μm depth from the top surface after three impacts. The fracture observation indicates that the flatness area is larger in the fatigue crack initiation (FCI) after LSPwC; meanwhile, the growth rate of fatigue crack is decreased. Lastly, the strengthening mechanism of LSPwC on the fatigue resistance was discussed based on the experimental results.