Effects of laser shock peening on fatigue performance of an ultrahigh-strength low-alloy steel fabricated via laser powder bed fusion

The present paper describes the main results from an experimental investigation into the effects of surface integrity modified via laser sock peening (LSP) on high cyclic fatigue (HCF) strength of an ultrahigh-strength low-alloy steel fabricated via laser powder bed fusion. Sets of specimens were treated by LSP under two wavelengths, from one to seven laser passes, and in two different confinement mediums to optimize the parameters for achieving superior fatigue performances. A set of baseline specimens before LSP are also tested for comparisons. The measured fatigue performances of the specimen sets were discussed as significantly affected by multiple surface integrity factors induced by different LSP process parameters such as surface roughness measured via confocal microscopy and mechanical hardness measured via nanoindentation. Moreover, the beneficial compressive residual stress fields near the surface were inferred indirectly using electron backscattered diffraction measured kernel average misorientation fields. Remarkably, results have shown that the endurance limit of the baseline material can be improved 54% via LSP surface processing. Results of comprehensive testing and characterization highlighting the LSP parameters to achieve peak improvements are presented and discussed. In closing, differences in the crack initiation and propagation amongst the specimens are discussed based on images of the fracture surfaces. The findings underscore the potential of LSP as a vital technology for enhancing the durability of engineering materials, while emphasizing the importance of establishing proper process parameters.