Fine-grained pretreatment process and superplasticity for INCONEL718 superalloy

A new method, superplastic forming (SPF) has been proposed for the production of complex-shaped INCONEL® alloy 718 components. For SPF, a microstructure with fine grain is one of the necessary factors. In this paper, one fine-grained pretreatment process to obtain a microstructure with fine grain (ASTM 11-12) for common INCONEL alloy 718 plate is reported, and this processing route includes a solution treatment at 1050 °C for 0.5 h with successive water quenching, hot-rolling (about 60%), cold-rolling (about 40%) and annealing treatment at 950 °C for 0.5 h. For the fine-grained INCONEL alloy 718, superplastic properties such as strain rate sensitivity and total uniform elongation are presented and discussed. The microstructural features such as grain size stability and cavitations following superplastic deforming are also presented. It is shown that the elongation to failure of the fine-grained INCONEL alloy 718 varied from 180 to 368.2% when the alloy was deformed at temperatures between 920 and 960 °C with initial strain rates ranging from 6.1×10−4 to 1.2×10−2 s−1, and the elongation to failure increases with decreasing strain rate. The strain rate sensitivity m of the alloy is always higher than 0.3. Dynamic grain growth was present during superplastic deforming for the alloy, and after superplastic deforming, cavities were found.