The effects of solution and intermediate heat treatments on the notch-rupture behavior of Inconel 718

Abstract

The effects of solution and intermediate heat treatments on the notch stress-rupture properties of Inconel 718 were investigated using commercial quality bar stock. It was determined that a solution heat treatment of 1038°C for as short a time as 20 min could render this alloy notch-sensitive by solutioning extensive quantities of the orthorhombic Ni₃Cb delta (δ) phase. Restoration of notch ductility subsequent to a 1038°C (20 min) solution heat treatment was accomplished by the insertion of a 917°C (10 h) intermediate heat treatment, prior to aging, during which significant quantities of the δ phase were precipitated. This intermediate heat treatment was not successful in restoring notch ductility to specimens which had been given longer, 1 h, solution heat treatments at 1038°C. A 954°C (3 h) intermediate heat treatment was also not successful in restoring notch ductility to specimens solution heat treated for 20 min at 1038°C. It was confirmed that the most important factors controlling the notch-rupture ductility in Inconel 718 are the size, quantity and distribution of the δ phase. The grain size of the material did not directly control the notch properties.