Microstructural and corrosion effects of HIP and chemically accelerated surface finishing on laser powder bed fusion Alloy 625

Hot isostatic pressing (HIP) and surface smoothing are two common post-processing methods to improve the mechanical properties of additively manufactured (AM) laser powder bed fusion (L-PBF) parts. While HIP increases part density and surface smoothing improves fatigue performance, it is unknown how, individually and together, these processes affect a component’s corrosion response. This study evaluated the resulting microstructures, surface roughness, and corrosion response of L-PBF Alloy 625 in the as-printed condition and after a standard HIP process to reduce porosity and after chemically accelerated vibratory finishing (CAVF) to improve surface finish. To assess any differences in build orientation, specimens evaluated were printed both vertically (Z-direction) and parallel (XY-direction) to the build platform. None of the specimens pitted during electrochemical evaluation, thus suggesting that the improved corrosion response of the CAVF specimens was due to a reduction in surface area. The Z-oriented as-printed specimen had significantly enhanced corrosion resistance due to a consistent distribution of alloying elements and a densely formed passive layer. Aside from the one exception, the results generally show HIP and CAVF result in minor impacts on the corrosion responses compared to as-printed L-PBF Alloy 625 despite differences in elemental distribution, surface morphology, and microstructural features. These post-processing methods may be employed to improve the mechanical properties of L-PBF Alloy 625 without concern of greatly altering the alloy’s inherently good corrosion properties.