The effects of hydrogen on the tensile properties of additively manufactured Hastelloy-X for hot parts

Mitsubishi Heavy Industries, Ltd. Group has made continuous efforts to develop hydrogen-related products, such as hydrogen-firing gas turbine, in pursuit of achieving carbon neutrality. Currently, we are considering the application of additive manufacturing technique for specific hot parts. Thus, we investigated the effects of hydrogen on the tensile properties of additively manufactured Hastelloy-X, one of the Ni-based superalloys for hot parts. In this study, Hastelloy-X specimens were fabricated by laser powder bed fusion (L-PBF) process. The relative density exceeded 99.9%. After fabrication, the specimens were heat-treated to relieve residual stress. In addition, rolled Hastelloy-X specimens were prepared for conventional manufacturing material. Subsequently, hydrogen was precharged into specimens via gas charging method and slow strain rate tensile tests (SSRT tests) were conducted on both hydrogen-charged and non-charged specimens at room temperature under atmospheric environment, with the strain rate of 5.0 × 10-5/s. The results of the SSRT tests indicated that the additively manufactured specimens were affected by hydrogen, with the relative elongation (the ratio of elongation of hydrogen-charged specimens to non-charged specimens) decreased. This decrease was slightly larger than that observed in the rolled specimen. From this result, it is considered that the microstructure and strength properties specific to the additively manufactured Hastelloy-X may have influenced its hydrogen embrittlement resistance.