Effects of micro-scale laser shock peening without coating on the tribological property of nickel-based powder metallurgy superalloy

The mortise region of powder superalloy turbine disks is highly susceptible to wear and fatigue fractures, necessitating advanced surface strengthening techniques. Conventional laser shock peening faces challenges in this application due to the area's confined geometry and complex surface topography, which hinder the uniform application of protective coatings. To address this, micro-scale laser shock peening without coating (LSPwC) is employed. This study examines the surface morphology and microstructure of LSPwC-treated samples using SEM and EDS, alongside friction and wear tests to evaluate improvements in wear resistance. Results reveal that LSPwC generates a gradient hardening layer on the surface, increasing hardness by 46.98 % (from 466.72HV to 686.00HV). The process induces thermomechanical loading, triggering material remelting and severe plastic deformation, which forms a heterogeneous remelted layer. This layer comprises unevenly distributed aluminum-rich oxides and MC-type carbides. The remelted layer's formation is attributed to rapid surface interactions during LSPwC, including localized melting, vaporization, shockwave propagation, and high cooling rates. The non-uniform deposition of remelted material elevates surface roughness from 0.593 to 2.522. Despite increased roughness, LSPwC-treated specimens exhibit significantly enhanced wear resistance compared to untreated samples. This improvement stems from the synergistic effects of the remelted surface layer, subsurface hardening, and compressive residual stresses, which collectively mitigate wear progression.