In Situ Imaging of High Cycle Fatigue Crack Growth in Single Crystal Nickel-Base Superalloys by Synchrotron X-Radiation

A novel X-ray synchrotron radiation approach is described for real-time imaging of the initiation and growth of fatigue cracks during ultrasonic fatigue (f=20 kHz). We report here on new insights on single crystal nickel-base superalloys gained with this approach. A portable ultrasonic fatigue instrument has been designed that can be installed at a high-brilliance X-ray beamline. With a load line and fatigue specimen configuration, this instrument produces stable fatigue crack propagation for specimens as thin as 150 {mu}m. The in situ cyclic loading/imaging system has been used initially to image real-time crystallographic fatigue and crack growth under positive mean axial stress in the turbine blade alloy CMSX-4.