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

¹ Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK
² Escuela de Ingeniería Aeronáutica y del Espacio, Plaza del Cardenal Cisneros 3, 28040 Madrid, Spain
³ Rolls-Royce plc, PO Box 31, Derby DE24 8BJ, UK

^a Corresponding author: ac773@cam.ac.uk

Abstract

ATI 718Plus^® is a polycrystalline Ni-base superalloy for aero-engine disc applications, which relies on the precipitation of η-phase (Ni₆Nb[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.