SEDL / STP / STP1263-EB / STP16446S

Effects of Cycle Type and Coating on the TMF Lives of a Single Crystal Nickel Based Gas Turbine Blade Alloy

Bressers, J
Institute for Advanced Materials, Joint Research Centre, ZG Petten,

Timm, J
Institute for Advanced Materials, Joint Research Centre, ZG Petten,

Williams, SJ
Rolls-Royce plc, Derby,

Bennett, A
Rolls-Royce plc, Derby,

Affeldt, EE
MTU Motoren und Turbinen Union München, München,

Pages: 12    Published: Jan 1996

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Abstract

Strain controlled thermo-mechanical fatigue cycles simulating the temperature-strain-time history at critical locations of blades of advanced aero gas turbines are applied to the single crystal nickel based alloy SRR99 in the uncoated and aluminide coated conditions. The TMF cycle selection includes a −135‡lag cycle and an in-phase cycle, with various R-ratios, T^min=300‡C, and T^max=1050‡C and 850‡C, respectively. The cycle-specific stress response is analyzed and discussed in terms of the accumulation of inelastic strain during the TMF tests, and the inelastic strain build-up is correlated with the cyclic hardening / softening behaviour. The number of cycles for initiating microcracks is measured by means of a computer vision system. Various modes of crack initiation and crack growth are observed and correlated with the TMF cycle type, with the strain range imposed, and with the ductile/brittle behaviour of the coating. The differences in TMF lives are discussed in terms of the material and TMF parameters