Effect of Laser Powder Bed Fusion Parameters and Hot Isostatic Pressing on the Microstructure and Mechanical Properties of C22 Alloy

A nickel-based Hastelloy C22 powder with a nominal composition was gas atomized and tested for its suitability as a feedstock in Laser Powder Bed Fusion (LPBF). The primary objective was to optimize laser power and scanning speed to manufacture specimens with maximum density. The optimal parameters identified were 150 W for power and 200 mm/s for scanning speed, leading to a relative density of 99.6%. Further experiments utilized increased power of 225 W and scanning speed of 1200 mm/s for higher production rates. Post-processing treatments including solution heat treatment and hot isostatic pressing (HIP) were conducted on the additively manufactured parts. Various analytical techniques were employed, such as optical microscopy and scanning electron microscopy, to evaluate microstructures, while microhardness and tensile tests assessed mechanical properties. The research revealed typical cellular and columnar dendritic structures in as-printed samples and highlighted the role of Mo-rich nanoparticles in strengthening the materials. HIP was found to significantly reduce defects in samples, whereas the impact of solution treatment on mechanical properties was less pronounced. The findings suggest that combining LPBF with HIP is essential for achieving near-full density in C22 alloys with desired mechanical characteristics.