Effect of heat treatment on the microstructure and properties of In 718 alloy prepared via PM-HIP

The Inconel 718 alloys were prepared by the power metallurgy hot isostatic pressing (PM-HIP). The obtained alloy ingots were subjected to heat treatments under three different parameters, holding at 980℃ for 1 hour followed by water quenching, then holding at 780℃ for 8 hours followed by air cooling, holding at 1020℃ for 1 hour followed by water quenching, then holding at 720℃ for 8 hours followed by air cooling, holding at 1080℃ for 1 hour followed by water quenching, then holding at 780℃ for 8 hours followed by air cooling, respectively. Tensile strength and microstructure of as-HIPed alloy were characterized via the Optical Microscope (OM), X-ray diffractometer (XRD), Scanning Electron Microscope (SEM), and Transmission Electron Microscope (TEM) et al. Results indicated that: the tensile strength of as- HIPed Inconel 718 alloy at room temperature is equivalent to that of forged parts, while the ductility is lower than that of the as-forged parts owing to the presence of prior particle boundaries (PPBs). Part of PPBs were eliminated during the solution treatment, thus the ductility of the as-HIPed alloy was improves. As the aging temperature increased, the γ''/γ' phases were over-aged, the strength of the material decreased and the ductility increased. The optimized heat treatment process was as follows: holding at 1020℃ for 1 hour followed by water quenching, then holding at 780℃ for 8 hours followed by air cooling.