Microstructure and tensile properties of IN718 superalloy aged with temperature/stress coupled field

The microstructures and tensile properties of the IN718 superalloy aged with and without stress were investigated. The results showed that in the temperature/stress coupled field, the coarsening of the γ″ phase and precipitation of the δ phase in the alloy were significantly accelerated. The alloys aged with stress showed lower strength and plasticity compared to those without stress, indicating that the degradation of the tensile properties was accelerated by the applied stress when aging, and such degradation was explained as follows. The accelerated coarsening and quantity reduction of the γ″ phase was caused by the coupled effect of temperature and stress. This weakens the strengthening effect of the γ″ phase on the alloy and the ability to capture and accumulate dislocations. When many needle-like δ phases precipitated near the grain boundaries, many micro-cracks formed, propagated rapidly, and connected along the zones without γ″ phases. Such microcrack propagation was unstable, resulting in plastic deformation localization.