Ni基一方向凝固超合金の高温疲労き裂伝ぱ駆動力に及ぼす結晶粒構成の影響

抄録

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.