Microscopic investigation of as built and hot isostatic pressed Hastelloy X processed by Selective Laser Melting

Highlights: • Columnar dislocation cells turn into columnar sub-grains after hot isostatic pressing. • As-built material exhibits nano-precipitates mostly on dislocation walls. • Hot isostatic pressed material additionally exhibits Cr₂₃C₆ at some grain boundaries. • Hot isostatic pressing causes decrease of micro hardness. -- Abstract: Microstructural characteristics of Hastelloy X produced by Selective Laser Melting have been investigated by various microscopic techniques in the as built (AB) condition and after hot isostatic pressing (HIP). At sub-grain level the AB material consists of columnar high density dislocation cells while the HIP sample consists of columnar sub-grains with lower dislocation density that originate from the original dislocation cells, contradicting existing models. The sub-grains contain nanoscale precipitates enriched in Al, Ti, Cr and O, located at sub-grain boundaries in the AB condition and within the grains after HIP. At some grain boundaries, micrometer sized chromium carbides are detected after HIP. Micro hardness within the grains was found to decrease after HIP, which was attributed to the decrease in dislocation density due to recovery annealing.