Development of Prior Particle Boundary Free Hot-Isostatic-Pressing Process for Inconel 718 Powder

Abstract

Hot isostatic pressed (HIPed) powder metallurgy (PM) Inconel 718 has the potential to be applied in turbine engines. However, the precipitation of high-density carbide particles along the prior particle boundaries (PPBs) leads to its poor ductility and is the main obstacle to be overcome if further and wider applications are pursued. In the past few years, we conducted research aimed at solving this problem, and a HIPing method that could eliminate the PPBs was developed. This paper summarizes the results in three parts: the first is on the influence of HIPing temperature on microstructure and tensile fracture modes of the HIPed alloy; several temperatures ranging from below the Laves incipient temperature to super-solidus were selected. In the second part, typical heat treatments for Inconel 718 were employed for mechanical property optimization of the HIPed alloy. It is found that HIPing at super-solidus temperatures could completely eliminate the PPBs, but the grain size is large and detrimental Laves phase also present. In the third part, a new HIPing process was developed, which consists of a short time holding above the solidus and a long time annealing below the incipient temperature of the Laves phase. This process could produce alloy free of PPBs and Laves phase. After heat treatment, the mechanical properties of the alloy are excellent.