Spark Plasma Sintering of Nickel-Based Superalloys: A New Route to Produce Dual-Alloy Turbine Disks

Spark Plasma Sintering was used to join powders of two nickel-based superalloysNickel-based superalloy containing over 40% volume fraction of γ’ phase and considered very difficult to weld. After 1 min of sintering, a very high relative density was reached, and both alloys were successfully solid-state joined without precipitationPrecipitation of detrimental phases in the diffusionDiffusion-affected zone. Solutioning of samples showed that a dual-alloy microstructureMicrostructure, composed of a coarse-grained alloy in the rim and a fine-grained alloy in the core, could be produced by this technique. In both as-received and fully-heat-treated states, assemblies exhibit tensile strengths at least higher than the weakest parent material. The heat-treatment sequence enables modulating strain partitioning during tension, leading to a more homogeneous deformation at very high stresses. Thus, failure occurs in the weakest parent material, far from the weld, with no alteration of the ductility, suggesting a sound joint has been produced during the short sintering time. The study on the viscoplastic response by means of tensile stress relaxationStress relaxation tests shows that a dual-alloy diskDisk technology has a high potential, resulting in improved creep propertiesCreep properties, chemical stability, and corrosion resistance in the rim section.