Theses and Dissertations Collection

The purpose of this study is to characterize the fatigue crack growth, creep-fatigue crack growth and creep crack growth of Inconel® 740H at elevated temperature. Tests were performed on solution annealed, heat-treated, compact tension specimens and performed in accordance with ASTM standards. Experimental tests were performed at 750℃ and 800℃. Loading conditions for fatigue crack growth were 15Hz, 0.25 Hz and 1/60 Hz whereas creep-fatigue crack growth conditions included a 60s and 6s hold time. Creep crack growth tests were performed at a constant load. This study characterized crack growth rate as a function of stress intensity, K. Fractography was also performed at various ∆K and K levels. At 750℃, it was found that crack growth rates were similar with the exception of the 1/60 Hz test. For the 60s hold test, fractography revealed more extensive secondary cracking than the 1/60 Hz test, leading to potential crack tip blunting. Exploratory work was performed at 800℃ and allowed for a temperature comparison as well as the evaluation of a creep crack growth test. An increase in temperature showed a change in creep-fatigue crack growth but little change in fatigue crack growth behavior for the material.