Fatigue-crack-propagation thresholds in a nickel-base superalloy at high frequencies and temperatures

Fatigue-crack-propagation (FCP) thresholds in a nickel-base superalloy at high frequencies and temperatures were investigated. Two different heat treatments were investigated, one yielding a relatively coarse grain size of 55 μm and another yielding a fine grain size of 6 μm. Tests were conducted at 100 Hz and 1000 Hz and at load ratios between 0.3 to 0.7. Scanning electron microscopy (SEM) was used to determine quantitative measures of fracture-surface roughness. Results showed that the roughness of the fracture surface increased as the load ratio was increased for both microstructures