Influence of stress on γ″ precipitation behavior in Inconel 718 during aging

Abstract

The precipitation behavior of the γ″ phase and mechanical properties in Inconel 718 alloy during aging under an external applied stress or internal quench-in residual stress were studied. The results show that nucleation and precipitation of the γ″ phase are strongly promoted by external stress in the early stages of aging. The γ″ precipitates exhibit homogeneous nucleation and always maintain a coherent relationship with the matrix. Further, the competitive growth of γ″ particles, namely coarsening, is the dominant process in the intermediate and late stages of aging. Aging under external stress may promote the nucleation rate, and therefore produce a higher number density of nuclei and, consequently, smaller precipitates after aging for 8 h. Moreover, the strength increment is sensitive to the mean size of γ″ precipitates. The decrease in strength is mainly due to the size reduction of precipitates in samples aged under external stress for 8 h. In the second experiment, the internal residual stress is distributed unevenly, resulting in inhomogeneous microstructure and mechanical properties in the workpiece.