Study of the influence of outgassing parameters, powder particle size and HIP temperature in the mechanical properties of IN718

In this work the influence of outgassing parameters on the strength and ductility and on the microstructure and oxygen content of IN718 has been studied because oxide and carbide precipitates on prior particle boundaries (PPB) limit interparticle bonding and are the main cause of poor ductility of HIPped IN718. Three outgassing temperatures were chosen in this work: room temperature, 800 °C and 1100 °C. It was found that outgassing at 800 °C and 1100 °C maintained the same oxygen level from the initial powder in the as-HIP samples and the ductility and strength were not improved after high temperature outgassing. It was found that HIP temperatures above the Laves/gamma eutectic are required to obtain good mechanical properties. The ductility was found to increase with the HIP temperature while the strength decreases. However at temperatures of the first stage of melting the increase in the ductility was related to incipient melting and not to a decrease of PPB content. The as-HIPped microstructures have been analysed, using scanning electron microscopy after different HIP processes, in order to understand the influence of the microstructure on the mechanical properties.