Effect of ultrasonic shot peening surface alloying on microstructure and tribological behavior of Inconel 718 superalloy

Ultrasonic shot peening (USP) surface alloying can enhance the surface strength and achieve the microstructure modification concurrently. In this paper, Inconel 718 superalloy was subjected to USP surface alloying with Nb powder, followed by post-annealing treatment. The microstructure and tribological behavior of the samples were investigated. After USP alloying and subsequent annealing, a Nb alloying layer with a thickness of similar to 7 mu m was fabricated on substrate surface, and a grain refinement layer with a depth of 100 mu m was formed. The introduced alloying layer promoted the precipitation of additional reinforcing phases through thermal activation, thereby engendering heightened hardness values within the sub-surface layer as compared to samples treated only by USP. The frictional test results showed that the lowest friction coefficient and smallest wear rate were obtained in sample treated by USP alloying and annealing, which was closely related to the highest hardness in the nearsurface layer. Moreover, the wear mechanisms of these samples were subsequently discussed.