Microstructures and mechanical properties evolution of IN939 alloy during electron beam selective melting process

Abstract Microstructure formation and transformation during electron beam selective melting (EBSM) is a unique process that has rarely been investigated, but can significantly influence the mechanical properties of parts. In this study, defect-free IN939 superalloy specimens were prepared and characterized using the EBSM method. It was found that the microstructures of the EBSM IN939 specimens consisted of primary, middle, and coarse γ' phases, and the ƞ phases had a gradient attribute. Transmission electron microscopy, selected-area electron diffraction, and energy dispersive spectroscopy tests were performed at different specimen heights, as well as a series of tensile tests. The results showed that the yield strength was influenced by the gradient microstructure. Higher yield strengths were obtained at the top of the fabricated specimens. Post-treatment was adopted to homogenize the gradient microstructure. Fracture analyses after the tensile test demonstrated the effects of different strengthening phases on the fracture behavior.