Crack behaviour under creep and creep-fatigue conditions of nickel-base superalloy MAR-M 247.

The crack initiation time and crack growth rate were determined in [1] for aero engine and stationary gas turbine engine blade material nickel-base-superalloy MAR-M 247. Long-term tests (up to 3 000h) at 850°C in conventional cast and 950°C in directionally solidified condition had been performed. Creep-, fatigueand creep-fatigue loading were applied. Component similar corner-crack-specimens had been examined. The crack starter notch had been applied using the razor-blade method, which provides a crack tip radius of less than 10 μm. Crack initiation times and growth rates had been correlated with the stress intensity factor KI. Additionally, the results of tests obtained on special designed cross drilled tubular specimens, simulating the cooling drills in real turbine blades, were compared with the results on corner-crack specimens. This allows an evaluation of the transferability of test results obtained on standard fracture-mechanic specimens to components subjected to creep-, fatigueand creep-fatigue interaction.