Creep Life Degradation and Microstructure Degeneration in a Low-Pressure Turbine Blade of a Military Aircraft Engine

Military aircraft engines operate under arduous environmental conditions with rapid throttle excursions as a part of its mission requirements. Life of an aircraft engine particularly of a military class is limited by the longevity of hot end components. Total technical life of a gas turbine component is dictated by the bulk properties while time between overhaul is decided by the aero-thermal degradation which in turn is influenced by the surface protective coating. In the present research, stress rupture tests were carried out to evaluate the creep life of blades while swelling of the coating and secondary reaction zone (SRZ) were evaluated to assess the coating damage. Further, an investigation was made to assess the degradation in creep life and microstructure degeneration during the service period when turbine blades made of wrought nickel-based alloy is provided with aluminide coating. Minimum creep rate and time to rupture are used as the characteristic parameters to evaluate the degradation in creep life. Coarsening of gamma prime ( γ ′) and degeneration of carbides was evaluated for microstructure degeneration in the bulk material. Degradation in coating life was evaluated by volume fraction of β-phase and development of SRZ in the coating.