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. It is known that oxide and carbide precipitates on particle boundaries (PPB) limit interparticle bonding and are the main cause of poor ductility of HIPped IN718. Therefore an extended study has been carried out of the reduction of oxygen content during outgassing. Three outgassing temperature 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. However the ductility and strength were not improved after high temperature outgassing. In addition samples that were reduced in hydrogen before outgassing at 800°C showed a reduction of 30% of oxygen in gas atomised powder with a 45+150µm particle size, but the ductility in as-HIP materials was decreased.
It was found that the minimum HIP temperature for obtaining good mechanical properties was 1220oC. The ductility was found to increase with the HIP temperature while the strength decreases. However this increase in the ductility was related to incipient melting and not to a decrease of PPB content. Furthermore it was found that smaller powder particle sizes helped to achieve higher ductility levels without decreasing the strength. 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.