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Home  >  Journal list  >  Journal of the Society of Materials Science, Japan  >  Vol.55  No.3 (2006)  >  pp.264-270

Journal of the Society of Materials Science, Japan
<<Previous article Vol.55  No.3 (2006)   pp.264 - 270 Next article>>

Effect of Grain Arrangement on Driving Force of Crack Propagation in High-Temperature Fatigue of Ni-Based Directionally Solidified Superalloy

Masato YAMAMOTO1), Takashi OGATA1) and Takayuki KITAMURA2)
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 Nickel-based directionally solidified (DS) superalloy, where the DS, load, and crack propagation axes are set to be perpendicular to each other. The magnitude of J-integral are estimated by the finite-element-method using 2-dimentional 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 (J-integral) 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 J-integral 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 J-integral which takes into accounts the factors and the crack propagation rate in transgranular crack shows a good correlation to a certain extent. The J-integral at the grain boundary cracking largely fluctuated and shows higher average magnitude than that in the other part. da/dN-J 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, High-temperature fatigue, Crack propagation, J-integral, Microstructure

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

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