The role of powder atomisation route on the microstructure and mechanical properties of hot isostatically pressed Inconel 625

Abstract

Abstract The powder's characteristics and its purity can greatly influence the properties of nickel (Ni)-base superalloys parts produced by near net-shape powder metallurgy hot isostatic pressing (NNS PM HIP) manufacturing process. In this study, Inconel 625 (IN625) powders produced using four different atomisation routes, argon, nitrogen, plasma and water atomisation (AGA, NGA, PA, WA, respectively) were investigated. The first section of this study is focused on the determination of powder characteristics which includes chemical composition, particle size distribution (PSD), tap density and powder's cross-section analysis, whereas the second section is about hot isostatic pressing (HIPping) of the four powder types and to assess the impact of the powder characteristics on the microstructure-property development after HIPping. To gain an understanding of the surface chemistry of the powders, X-ray photoelectron spectroscopy (XPS) analysis were carried out on the surface of the four powders. The latter analysis highlighted fundamental differences on the powder's surface, especially the differences in the surface and near-surface distribution of the alloying elements i.e. C, O, Cr, Mo and Nb present in the alloy chemistry. The micrographs of the four IN625 hot isostatically pressed (HIPped) powders revealed a fully dense microstructure with the presence of prior particle boundaries (PPBs). The atomisation route greatly impacted the nature and amount of PPBs, as well as on the fractions and sizes of oxides, carbides, oxycarbides and oxycarbonitrides precipitates. WA showed the most severe presence of PPBs, followed by NGA, AGA and lastly PA. The powder quality has a greater impact on the mechanical properties of as-HIPped materials, especially on ductility. Overall, PA HIPped IN625 possessed the optimum balance between tensile strength, ductility and Charpy impact properties once compared to the others and match the properties to wrought IN625 material.