Necking characteristics and dynamic recrystallization during the superplasticity of IN718 superalloy

The necking extent of the superplasticity of IN718 alloy is difficult to quantificationally evaluate because of its point fracture (with extreme small final fracture area) after failure. In this investigation, we have defined a necking angle to donate the necking extent after failure and systematically investigated the superplastic behavior of the alloy at temperatures between 935 °C and 1010 °C in strain rate range 5×10−4-10−2 s−1. In the temperature range 935-980 °C, the elongation was found to decrease with the increasing strain rate while the necking angle (extent) increased because softening source provided by the dynamic recrystallization increased with the increasing strain rate at necking zone. In contrast, at 1010 °C, due to a good balance between the grain refinement by recrystallization and the dynamic grain growth, a peak elongation of 225% was obtained at 10−3 s−1. Our study has emphasized the vital role of the dynamic recrystallization during the superplasticity of IN718 alloy.