High temperature fatigue crack growth slip irreversibility

Fatigue crack growth (FCG) and eventual fracture can lead to catastrophic failures in an elevated temperature environment. Haynes 230, a nickel-based superalloy, was found to have FCG rates over an order of magnitude greater at 900 °C compared to room temperature results. FCG experiments were performed using digital image correlation (DIC). Crack closure in the wake revealed no significant differences. Crack tip mechanisms were then investigated and revealed an order of magnitude higher slip irreversibly at 900 °C compared to room temperature magnitudes. These results were captured at low magnification inspiring further development of a high resolution, high temperature capable DIC technique. As proof of concept, an interrupted tensile experiment was performed at 700 °C with high resolution DIC measuring sub-grain strains. High strain heterogeneity was revealed with concentrations at grain boundaries. Future work will extend the technique to slip irreversibility experiments to measure grain boundary resistance to crack growth.