Optical and electron metallographic (SEM) examination was performed on MARM-421 samples subjected to controlled furnace exposures, to quantify the microstructural changes associated with the prolonged high-temperature exposures. Gamma prime size measurements were used to generate a mathematical model, based on diffusion-controlled kinetics, designed to estimate temperatures. This computational technique was utilized to estimate exposure temperatures of turbine blades that had seen service in land-based gas turbine engines. The engines had accumulated from 1200 to more than 98,000 hours, operating under a variety of conditions. The procedure is generally applicable to commonly used gamma prime strengthened nickel-base superalloys.

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