The purpose of this project is to establish a broad based understanding of the microstructural factors controlling the high temperature properties (including creep and fatigue life) of turbine blade and disc alloys.
A range of superalloys proposed for aeroengine turbine disc applications are being compared in the time-dependent fatigue crack growth regime, where oxidation, creep and fatigue processes interact synergistically. A number of alloys: N18, Udimet720Li and low solvus high refractory (LSHR) alloys will be compared, in both powder metallurgy and cast and wrought form.
Both sub-solvus and super-solvus solution heat treatments are being investigated. The project is studying fatigue initiation and propagation mechanisms in air and vacuum for these alloys over a range of temperature (e .g. 650oC-725oC) providing a mechanism map for the initiation and growth of fatigue cracks. Tests are being carried out on notched bend bars to study initiation and early fatigue crack growth in the local stress field associated with a notch simulating a turbine blade root fixing. Relevant crack propagation studies are also being carried out, and mean stress level and varying stress range effects studied.