CONTRIBUTIONS OF OXIDATION AND CREEP TO HIGH TEMPERATURE FATIGUE CRACK SUSCEPTIBILITY IN WASPALOY
The aggressive mechanical and environmental conditions in the hot sections of jet engines leads to creep and oxidation enhanced fatigue damage on high-performance metal components. Understanding the relative contribution of oxidation, cyclic damage accumulation, and creep is needed. Crack growth kinetics data were gathered on SENT fracture mechanics specimens using the direct current potential drop method. Specimens were tested in lab air and vacuum at elevated temperature at a constant ΔK and loaded according to a trapezoidal waveform with dwells ranging from 1 to 300 seconds. Plastic deformation and dislocation cell structure along the crack wake was assessed using high resolution electron backscatter diffraction and TEM. Quantitative comparisons of crack growth kinetics and deformation character for each test condition are performed and show variations in crack growth rates and size and intensity of plastic damage along the crack wake. These results provide insight into the contribution of creep and oxidation to crack growth and inform modeling high temperature fatigue behavior.