Dissimilar linear friction welding of Ni-based superalloys

Abstract

Linear friction welding is a solid-state, near-net shape manufacturing method for metallic alloys which is characterised by complex deformation and metallurgical actions at the weld interface. However, a lack of understanding of the welding parameter interaction and subsequent welding mechanisms is hindering the joint integrity enhancement of dissimilar linear friction welding. In this study, we investigated the influence of various process parameters on macro/micro-formation, microstructural evolution, and properties to establish optimal welding conditions for the sound linear-friction-welded joint integrity of dissimilar superalloys, IN718, and the powder metallurgy FGH96. Increased oscillation frequency or decreased applied pressure promoted continuous dynamic recrystallisation and grain refinement, although discontinuous dynamic recrystallisation remained dominant. Enhanced dissolution of the strengthening phases (γ′ phase on the FGH96 side and δ phase on the IN718 side) was observed from the thermomechanically affected zone to the interface. The subsequent correlation between the microstructure and mechanical properties indicated that solid–solution strengthening was the dominant mechanism for enhancing interfacial bonding, which was promoted by mutual material deformation on both sides. Accordingly, to achieve synergistic plastic deformation in dissimilar linear friction welding, an optimisation strategy of welding parameter combination was proposed and validated by investigating hot compressive dissimilar Ni-based superalloys. The results of simulations of sub-size workpieces showed that using linear friction welding to manufacture bimetallic bladed disks, from conception to completion, was feasible. The paper offers an integrated solution for the full-scale manufacturing of an IN718/FGH96 blisk using linear friction welding based on microstructure–property interactions and relevant simulations, which can ideally serve as the basis for future bimetallic bladed disk manufacturing.