Microstructure and mechanical properties of an inertia friction welded INCOLOY alloy 909 -INCONEL alloy 718 joint for rotating applications

摘要

Inertia welding is a common practice to join axially symmetrical parts for aero-engine applications. The shaft for a new advanced high-pressure compressor will be produced by joining the high strength superalloys INCOLOY~R alloy 909 (Incoloy909) and INCONEL~R alloy 718 (IN718). IN718 is the work-horse nickel-iron-chromium alloy for a variety of parts for aero-engine applications due to a good combination of relevant mechanical properties, good corrosion resistance and easy fabricability. Incoloy909 is a nickel-iron-cobalt alloy used in aero-engines due to an interesting combination of a nearly constant low coefficient of thermal expansion combined with a constant modulus of elasticity and high strength over a wide range of temperatures. Both alloys are strengthened by precipitation-hardening through additions of niobium and titanium. Ring shaped specimens of fully heat-treated Incoloy909 and IN718 are joined by inertia welding. The microstructure in the welded zone is investigated by optical microscopy and transmission electron microscopy with the focus on the Incoloy909 side. Post-weld heat-treatments (PWHT) are evaluated by microstructural investigations and by hardness measurements. The chosen PWHT is characterized by its tensile, creep and load controlled fatigue properties. The results of the mechanical tests are described in terms of the microstructural changes observed in the welded zone.