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Vol. 71 (2007) No. 9 P 693-698



  A failed 2nd stage high-pressure turbine blade taken from one of the P & W 4000 series engines had been examined in order to estimate the metal temperature at the damaged part of the blade during service. By assuming that the equlibrium microstructure had been achieved in the damaged area, this temperature could be determined from correlations between the chemical composition of γ phase measured experimentally and predictions of the NIMS in-house alloy design program. To confirm the validity of this procedure, another experiment was conducted in parallel on a crept specimen of PWA1484 under the condition of 1100°C-137MPa; the results indicated that metal temperature could be deduced by the same method with an accuracy of ±25°C at 1095°C. Analysis for the failed turbine blade revealed that the surface of the inner cooling path had been oxidized, and many cooling holes were blocked by oxide scales. This oxidation process might be induced by sulphidation as a sulfur-enriched region could be detected at the front of oxide layer. In addition, coarsened γ and γ′ microstructures were observed in the area of the damaged part. The estimated metal temperature of the failed region of the blade was above 1100°C; this might be the result of insufficient heat dissipation through cooling channels due to the blockage by oxide scales.

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