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Journal of the Society of Materials Science, Japan

Effect of Grain Arrangement on Driving Force of Crack Propagation in HighTemperature Fatigue of NiBased Directionally Solidified Superalloy

Masato YAMAMOTO^{1)}, Takashi OGATA^{1)} and Takayuki KITAMURA^{2)}

1) Central Res. Inst. Elect. Power Industry 2) Dept. of Eng. Phys. & Mech., Kyoto Univ.

Crack propagation test is carried out in high temperature fatigue of a Nickelbased directionally solidified (DS) superalloy, where the DS, load, and crack propagation axes are set to be perpendicular to each other. The magnitude of Jintegral are estimated by the finiteelementmethod using 2dimentional models; (i) with the actual crack shape and grain configuration, (ii) with the straight crack in homogeneous body, and (iii) with the actual crack shape in homogeneous body. The driving force (Jintegral) of crack propagation is affected by two factors, the local crack propagation direction and anisotropy due to the grains. The former causes the sporadic drop of Jintegral at the point where the crack direction is largely apart from the direction normal to the load axis. The latter causes the stepwise change in a (crack length)  J relationship which directly relates to the change of crack propagation rate in transgranular cracks. Then, the relationship between the Jintegral which takes into accounts the factors and the crack propagation rate in transgranular crack shows a good correlation to a certain extent. The Jintegral at the grain boundary cracking largely fluctuated and shows higher average magnitude than that in the other part. da/dNJ relation reveals that the intergranular crack has weaker resistance against propagation than that in the transgranular one, though it shows eminent fluctuation.

Keyword: Directionally solidified superalloy, Hightemperature fatigue, Crack propagation, Jintegral, Microstructure

Received: May 16, 2005
Published online: April 26, 2006 
Copyright (c) 2006 by The Society of Materials Science, Japan 
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