Effect of solution treatment temperature on the microstructure and tensile properties of P/M (HIP) processed superalloy Inconel 718

Abstract

Inert gas atomized superalloy Inconel 718 powder was hot isostatically processed (HIPed) at 1200°C / 120 MPa / 3h. This material was then subjected to a standard heat treatment schedule adopted for wrought IN 718 (955°C / 1 h. / water quenching and two - step ageing at 720°C / 8 h. / furnace cooling to 620°C / 8 h. / followed by air cooling to room temperature), which showed substantial improvement in strength but a drastic decrease in ductility. Since, the solution treatment temperature has a significant influence on microstructure development, the HIPed compacts were subjected to various solution treatment temperatures between 850 and 1270°C, while the same ageing treatment was retained. The microstructure of the compacts in the as - HIPed, solution treated and aged conditions was studied in detail. The tensile properties of these samples were evaluated at room temperature and at 650°C. The microstructure corresponding to the solution treatment temperature of 1270°C, showed incipient melting at the particle boundaries leading to enhanced bonding across the particles and resulting in a considerable improvement of ductility.