Experiment study on improving fatigue strength of K24 nickel based alloy by laser shock processing without coating

Abstract:

Laser shock processing without coating (LSPwC) is a novel surface treatment, which can effectively increase the fatigue strength of metal materials by introducing compressive residual stress and microstructural changes. The objective of this work is to improve the fatigue resistance of K24 nickel based alloy by LSPwC. 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 showed that the fatigue strength of K24 alloy was enhanced and improved from 282MPa to 328MPa 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 indicated that residual stress presented compressive state on the superficial layer with about 150μm depth and the maximum value reaches -595MPa. The microhardness is about 526 HV0.5 with about 100 μm depth from the top surface after three impacts. The fracture observation indicated that the flatness area was larger in the FCI after LSPwC, meanwhile, the growth rate of fatigue crack was decreased. Lastly, the strengthening mechanism of LSPwC on the fatigue resistance was discussed based on the experimental results.