Effect of solution heat treatment and hot isostatic pressing on the microstructure and mechanical properties of Hastelloy X manufactured by electron beam powder bed fusion

Abstract

• As-built PBF-EB Hastelloy X has anisotropic microstructure and mechanical behavior. • Grain coarsening from solution heat treatment and HIP reduced the yield strength. • Crystallographic texture along 〈100〉 remained unaffected even after post-treatment. • Anisotropy in yield strength and ductility weakened following post-treatment. • Solid solution strengthening is the main contributor towards overall yield strength. Prior to the application of AM components for critical applications, it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties of such parts. In this study, efforts were made to achieve an in-depth understanding of the effect of post-fabrication Solution Heat Treatment (SHT) and Hot Isostatic Pressing (HIP) on the microstructure and mechanical properties of Hastelloy X parts built by electron beam powder bed fusion (PBF-EB) process. The effects of SHT and HIP on porosity, microstructure, texture and mechanical properties have been investigated and compared with that of as-built PBF-EB Hastelloy X. Post-fabrication HIP treatment led to a significant reduction in the porosity content, whereas no notable difference in porosity was observed between SHT and as-built parts. There was no evidence of any recrystallization occurring following the post-fabrication treatments as elongated columnar grain structures observed within as-built part were found to be maintained even after SHT and HIP process alongside the strong 〈100〉 crystallographic texture. Emphasis was laid upon understanding the influence of SHT and HIP on mechanical properties through stress-strain curves and work-hardening behaviour.