Evaluation of Fatigue Crack Propagation in The Post-Service Gas Turbine Vane

Abstract

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.

OS12F008 Assessment of Fatigue Crack Propagation Behavior near Crystallographic Orientation Boundaries in Polycrystalline Ni-base Superalloys

“…In this work the miniature compact tension (CT) specimens illustrated in Fig. 2 were extracted from the cast superalloy rods for the fatigue test [6]. The geometry of specimen was designed so that it was almost proportional to that recommended in ASTM E647 [8], except for the specimen thickness.…”

“…These loadings inevitably cause many types of damages and degradations in components during the operation period. Materials used in them, especially Ni-base superalloys, are so expensive items that they can be a substantial part of an operating and a maintenance budget [1][2][3][4][5][6][7]. Therefore, it is of considerable technical and financial benefit if the condition of the blades can be assessed and their remaining life determined.…”

“…Therefore, it is of considerable technical and financial benefit if the condition of the blades can be assessed and their remaining life determined. Whilst some efforts have been made to estimate the remaining life based on the crack assessment, there has not been well-established method and methodologies yet [1][2][3][4][5][6][7]. Some reasons are responsible for these difficulties.…”

“…The interaction between crack and grain boundaries has not been known well, while it may be significant especially in cast Ni-base supperalloys because the dimension of components is generally in same order as grain size of material [9].. In addition, there are also technical hurdles to get test results using a miniature samples; here knowledge is required from local level and not from macro level by means of standard size specimens [6].…”

Fatigue Crack Propagation in Thin‐Wall Superalloys Component; Experimental Investigation via Miniature CT Specimen

“…Some reasons are responsible for following problems: i) Fatigue crack propagation (FCP) tests are usually carried out using standard size specimens (5-10mm thickness) [10], although actual crack growth takes place in thin wall components with cooling systems, where the wall thickness is about 0.5-1.0mm. The thickness dependency of crack propagation may lead to a discrepancy between the laboratory results and the actual crack growth [11]. ii) Little is known quantitatively about effects of both the crystal and grain boundary orientation [12,13].…”