Precipitation and Residual Stress Relaxation Kinetics in Shot-Peened Inconel 718

Mechanical surface treatment by shot peening followed by aging at 700 and 740 °C was performed on Inconel 718. A previously proposed XRD method (Ref 10) for the quantitative phase analysis of Inconel 718 allowed for the determination of the precipitation kinetics of the γ'' phase in the shot-peened layer and the matrix, respectively. The residual compressive stress field induced by shot peening and its relaxation behavior during aging were also determined. The relaxation process can be described by the Zener-Wert-Avrami function. The precipitation rate in the γ'' phase in the shot-peened layer is greatly accelerated, which causes differences in the γ'' phase amounts between the skin and the core during aging, especially during the initial stage. The high precipitation rate of the γ'' phase in the shot-peened layer can be interpreted by the nonequilibrium segregation of niobium.[PUBLICATION ABSTRACT]