Date of Graduation
Recently developed Î³-Î³â€²-Î² three phases governing INCONEL* alloy 783 is the result of an extensive superalloy development program aimed at improving environmental-induced intergranular cracking resistance. Formation of intermetallic nickel aluminide Î² phase in alloy 783 is essentially resistant for the general oxidation. In this study, commercial alloy 783 was subjected to various metallurgical processing including heat treatments with Î² aging/without Î² aging, addition of 3% Cr into alloy, and thermo-mechanical processing (TMP). The corresponding microstructures were evaluated by means of the optical microcopy, SEM and TEM. These processed materials were subjected to the fatigue crack growth and sustained loading crack growth tests to investigate the effects of Î² precipitates on crack growth process, especially on the time-dependent crack growth behavior. It was found that Î² precipitates in alloy 783 play a very significant role in controlling SAGBO-induced crack growth process. Properly controlling the microstructure and morphology of Î² precipitates by different metallurgical processing can improve the resistance to environmental-induced damage. Based on the experimental results, a phenomenological model, which could describe crack growth behavior of alloy 783 subjected to the different metallurgical processing, were developed through introducing a universal time-dependent factor, Î±(t, T). Combining the physical interpretation of SAGBO-induced degradation mechanism and generated data, a 1-D stress-assisted oxygen diffusion model at crack tip along grain boundaries was proposed. This model was utilized to characterize crack growth behavior and crack incubation time in alloy 783 without Î² aging under sustained load condition. The good agreement between model prediction and experimental results were obtained. *INCOLOY and INCONEL are trademarks of the Special Metals Corporation. Huntington, West Virginia.
Ma, Longzhou, "Effects of nickel-aluminum-beta precipitates on crack growth behavior in INCONEL alloy 783." (2001). Graduate Theses, Dissertations, and Problem Reports. 9335.