Cyclic oxidation and long-term isothermal exposure tests were conducted on GTD-111 and IN-738 alloys to evalaute the variation of oxidation and gamma prime particle coarsening bheavior between these alloys. Cyclic oxidation behavior of these alloys was compared by plotting the weigth change of the test specimens as a function of thermal cycles. The results showed that GTD-111 was less resistnat to oxidation compared to IN-738. To characterize oxide scale, short-term isothermal oxidation tests were conducted at two temperatures, and spalled oxide was collected and analyzed by EDS as a function of aging. The composition of the oxide varied between the materials. The long-term exposure tests (up to 10,000 hours) were conducted at four temperatures to assess gamma prime particle coarsening behavior. Metallographic work was performed on both the cyclic oxidation and isothermally aged samples to characterize oxidation attack and gamma prime coarsening as a function of aging time and thermal cycles. At all aging temperatures and/or times investigated, the gamma prime particles in the GTD-111 specimens were coarser than in IN-738. The variation of the oxidation and the gamma prime coarsening behavior between these alloys is discussed in terms of chemistry differences between IN-738 and GTD-111.
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