Shaped metal deposition of a nickel alloy for aero engine applications

Manufacturing trials in support of shaped metal deposition (SMD) as a commercial process for the near net shape processing of aero engine components are reported. Initially, relatively simple multi-pass linear weld deposition beads employing the nickel-based polycrystalline superalloy Alloy 718 were characterized, to define the microstructural condition of the substrate and superimposed welds. Subsequently, a developmental combustion outer casing was fabricated via a hybrid-manufacturing route. This casing was formed from a forged ring with additive features, which included an internal, circumferential flange of Alloy 718, built up via an automated, high volumetric deposition rate MIG process. Under both circumstances, in the post-deposition heat-treated condition (aged but not solution heat treated), the γ matrix contained laves micro-stringers, typically orientated parallel to the axis of epitaxy, with associated δ phase precipitation. On the micro-scale, such micro-stringers were intimately associated with cracking or shrinkage porosity. Bi-axial stress fields imposed during the cooling of the large-scale casing structure appear to influence the macroscopic organisation of these weld deposition defects.