Additive manufacturing of γ' precipitate-strengthened nickel-based superalloy UNS N07001 by electron beam melting: Effects of post-heat treatment on microstructure and mechanical properties

Abstract

The γ' precipitate-strengthened nickel-based superalloy UNS N07001 is widely used in gas turbines because of its high-temperature strength and corrosion resistance. In this paper, optimal process parameters of electron beam melting were determined to shorten the lead time of UNS N07001. In addition, the effects of post-heat treatment on the microstructure and mechanical properties of UNS N07001 were evaluated. The optimal process parameters were determined by evaluating the appearance, surface roughness, relative density, and Brinell hardness of UNS N07001 blocks built with 32 different parameter combinations. The UNS N07001 sample produced using the optimal parameters was subjected to hot isotropic pressing (HIP) and solution treatment and aging (STA). Microstructural observation, precipitate analysis, and tensile tests of the resulting specimens were conducted. Microstructural observations and precipitate analysis revealed that the as-built specimen contained cracks and pores. These defects disappeared after HIP treatment. Additionally, STA after HIP treatment resulted in a high content of fine γ'-phase precipitate. Tensile tests revealed that the mechanical properties of the specimen were barely changed by HIP treatment, whereas STA after HIP markedly improved the mechanical properties of the specimen to a level comparable to the requirements for the wrought material. The beneficial mechanical properties of the specimen treated by HIP and STA may be attributed to the high content of fine γ' precipitates.