Isothermal and Cyclic Oxidation Behavior of Turbine Blade Alloys

Abstract

Oxidation behavior of two nickel-based turbine blade alloys has been investigated at three temperatures ranging from 950°C to 1066°C. Thermogravimetric analysis (TGA), isothermal exposure and cyclic oxidation tests were conducted on GTD-111 (Ni-14.1Cr-3.7W-9.2Co-1.5Mo-3.1A1-4.9Ti-0.02Cb-2.93Ta-0.11C) and IN-738 (Ni-16.0Cr-2.6W-8.1Co-1.6Mo-3.5A1-3.4Ti-0.7Cb-1.6Ta-0.10C) blade alloys. TGA results showed that the oxidation kinetics of both alloys obey parabolic rate laws. The GTD-111 material exhibited a higher parabolic rate constant than IN 738 at all temperatures investigated. Cyclic oxidation behavior of these alloys was compared by plotting the weight change results as a function of thermal cycles. Consistent with the TGA results, cyclic oxidation test results also showed that GTD-111 was less resistant to high-temperature oxidation as compared to the IN-738 alloy. To characterize the oxide scales, a series of short term isothermal oxidation tests were conducted and the spalled scale after oxidation exposure was collected and analyzed by energy-dispersive x-ray analysis (EDX) as a function of aging time. The composition of the scales varied between the alloys. The variation of oxidation behavior of these alloys is discussed with respect to the composition differences between the two alloys.