Evolution of secondary phases in alloy ATI 718Plus®during processing

Abstract

ATI 718Plus® is a polycrystalline Ni-base superalloy for aero-engine disc applications, which relies on the precipitation of η-phase (Ni6 Nb[Al,Ti], D024 ) at grain boundaries for resistance to intergranular failure and grain size control. The nucleation and evolution of the η particles have been examined throughout the manufacturing process. During hot working below the η solvus, existing precipitates lose their orientation relationship with the matrix and become aligned with the forging flow. During heat treatment, a dual morphology develops by the uniform growth of those incoherent precipitates into coarse plates, together with the new nucleation of thin lamellae from selected grain boundaries. The balance between the two morphologies in the final component can be achieved by controlling precipitation and dissolution processes during forging.