Cavitation and failure in a fine-grained Inconel 718 alloy having potential superplastic properties

Experiments were conducted to evaluate the failure behavior and the cavitation characteristics of an Inconel 718 alloy with a potential for superplastic forming. Tensile testing was performed on the as-received alloy at a temperature of 950 °C and using initial strain rates from 10−4 to 10−2 s−1. All specimens were pulled to failure and then examined using optical microscopy and a quantitative image analysis facility. The results show evidence for extensive necking at a strain rate of 10−2 s−1 but there is less necking and more internal cavitation at the lowest strain rate of 10−4 s−1. Quantitative measurements of internal cavitation show the area fraction of cavities and the average cavity area both increase with increasing strain and with decreasing strain rate. It is concluded that the cavities grow initially by diffusion but there is an important additional contribution from cavity interlinkage.