Investigation of surface integrity in inconel 718 enhanced by heat treatment, ultrasonic impact and multi-media jet processing.

This paper explores the surface characteristics of Inconel 718 following a composite surface enhancement process that combines heat treatment, ultrasonic impact, and solid particle-water jet (HT-UIT-SPEWJ). The research focuses on analyzing the impact of various process parameters on the microstructure, surface roughness, microhardness, residual stress, and XRD patterns of the treated material. The results indicate that after HT-UIT-SPEWJ treatment, the Inconel 718 surface predominantly features "crater-like" formations and debris adhesion. There is a notable inverse relationship between surface roughness and aging temperature, with aging temperature emerging as the most critical factor affecting surface roughness. The surface roughness initially decreases and then increases with the ultrasonic shock frequency, reaching its lowest value of 1.552 μm at 140 Hz. A similar trend is observed with jet pressure, where surface roughness decreases initially and then increases. In addition, the study reveals that the surface microhardness and residual compressive stress of the specimens are significantly improved after treatment, and both show a positive correlation with aging temperature. Microhardness exhibits an initial rise, followed by a decrease and another increase as ultrasonic shock frequency increases, while residual compressive stress peaks at -1027.47 MPa at 120 Hz before decreasing. Similar patterns are observed with varying jet pressures for both microhardness and residual compressive stress. The HT-UIT-SPEWJ treatment induces considerable residual compressive stress, penetrating depths greater than 250 μm, and results in prominent diffraction peaks corresponding to γ(111), γ(200), and γ(220) in the treated specimens.