The effects of Hot Isostatic Pressing on parts fabricated by binder jetting additive manufacturing

Hot Isostatic Pressing (HIP) is a technique of applying high pressures through a fluid medium at high temperatures to enclosed powders, castings and pre-sintered metal parts to eliminate porosity. Due to uniform volumetric shrinkage expected from this process, it can be a useful post-processing technique for complex-geometry parts fabricated using Additive Manufacturing (AM) techniques. In order for the technique to work effectively, parts are typically required to have a minimum density of 92%, where surface porosity is closed. While HIP has been used in conjunction with powder bed fusion AM processes, its use for parts made using Binder Jetting (BJ) has not been investigated in detail due to the limitations of BJ in fabricating sufficiently high-density parts without infiltration. In this work, detailed investigations on the effect of HIP on BJ parts printed from three different powder configurations, which led to varying levels of porosity, are performed. The effects of HIP on the density, microstructure, tensile strength, and ductility of the resulting parts is reported. A maximum density of 97.32% was achieved by HIP of printed and sintered parts created via bimodal powders. Both the tensile strength and ductility were found to improve following HIP, which suggests that the reduction in porosity is predominant compared to the detrimental effects of grain coarsening. © 2018 Elsevier B.V.