Local area fatigue crack propagation resistance of a retired gas turbine vane made of a Ni-based superalloy which had been operating for about 20000 h. in a 1100 °C level land-based gas turbine, was experimentally evaluated. Here, special efforts were made to build up a new testing apparatus to assess the fatigue crack propagation resistance, using the miniature size specimens extracted from the vane. The miniature specimens were extracted from the leading and the trailing edges, respectively. It was shown that the fatigue crack grew associating with the rate significantly higher at the trailing than at the leading edge part. It was also indicated that the crack propagation rates in the miniature specimen were generally higher than those in the standard size specimen. Furthermore, it was also shown that an application of a simple reheat treatment was effective to recover the crack propagation resistance for the post service vane.

Abstract. Degree of long term degradation damage of a retired gas turbine vane made of a Ni-based superalloy which had been operating for about 20000 hrs in a land-based gas turbine, was experimentally evaluated, through an assessment on the change in fatigue crack propagation resistance. For the purpose, a new testing apparatus has been developed to measure the local area fatigue crack propagation resistance, by extracting the miniature size compact tension specimens from the vane, where the specimens were extracted from the leading and the trailing edge, respectively. It was shown, the propagation rate of the crack that grew at the trailing edge part was significantly higher that that at the leading edge part. It was also shown that the crack propagation rates in the miniature specimen were generally higher than those in the standard size specimen. In order to explore an possibility to recover the degradation damage, the effect of a simple reheat treatment on the fatigue crack propagation resistance was also investigated.

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