The effect of hot isostatic pressing pressure level and solution annealing cooling rate on CM247 LC nickel-based superalloy processed by laser-based powder bed fusion

In the present work, CM247 LC samples produced by laser-based powder bed fusion (PBF-LB) were heat treated inside a hot isostatic pressing (HIP) furnace (HIP quench treatment) at 1260 degrees C for 3 h to combine the solution annealing with the elimination of defects of the additively manufactured parts. In particular, the effects of different applied pressures (50-170 MPa) and cooling rates (from 162 to 2450 degrees C/min) on the final densification, grain coarsening, and gamma' precipitation were studied. The results were also compared to a sample heat treated in a low-pressure furnace and gas-quenched at 195 degrees C/min. The study revealed that the applied pressure has a negligible effect on densification, grain coarsening, and the size and shape of gamma', which is always irregular after solution annealing, independently from the cooling rate. For this reason, first aging was subsequently applied at 1080 degrees C for 4 h to HIP-quenched samples, revealing that this step of treatment is effectively responsible for the final cubic shape of gamma', even if a starting irregular morphology is considered. Finally, additional samples were heat treated in an air furnace and air cooled to room temperature prior to the HIP quench; this procedure allowed assessing the solutioning effectiveness of the HIP quench with coarse precipitates typical of conventional processing (e.g., investment casting). Overall, this study underscores the efficacy of the HIP quench in enhancing microstructural attributes and mitigating defects, providing valuable insights for enhancing the properties of challenging Ni-based alloys fabricated through additive manufacturing techniques.