Dissolution kinetics of δ phase and its influence on the notch sensitivity of Inconel 718

The dissolution kinetics of 8 phase in Inconel 718 at 980 degrees C, 1000 degrees C and 1020 degrees C and its influence on high temperature notch sensitivity have been studied using a quantitative X-ray diffraction (XRD) method and high temperature stress rupture life tests of notched specimens. The amount of 6 phase decreases gradually during holding time at 980 degrees C, 1000 degrees C and 1020 degrees C. The 6 phase will be fully dissolved in the austenitic matrix at 1020 degrees C for more than 2h. A certain amount of 6 phase still exists after holding at 980 degrees C and 1000 degrees C for times up to 6h; the amount remaining are 3wt.% and 0.6wt.%, respectively. The dissolution rate remains at a high level at the beginning, and then decreases gradually with an increase of holding time. A dynamic equilibrium state can be approached after holding at 980 degrees C for more than 30min and at 1000 degrees C for more than 2h. The alloy with 6 phase amounts higher than 0.62wt.% does not exhibit notch sensitivity, whereas serious notch sensitivity exists if the concentration is below 0.43wt.%. (c) 2006 Elsevier Inc. All tights reserved.