報告書番号

Q04006

タイトル（和文）

Ni基一方向凝固超合金の高温強度評価法の開発 -第6報：疲労き裂伝ぱの駆動力に及ぼすき裂伝ぱ経路および結晶粒構成の影響-

タイトル（英文）

Development of high temperature strength evaluation method for nickel-based directionally solidified superalloy -6th report: Effect of crack propagation path and grain configuration on fatigue crack driving force-

概要 （図表や脚注は「報告書全文」に掲載しております）

Ni基一方向凝固（DS）超合金の結晶成長方向に対し荷重軸が平行なL試験片と，結晶成長方向，荷重軸，およびき裂伝ぱ方向を直交する3つの軸にそれぞれとったT試験片に対し，高温疲労き裂伝ぱ試験を実施した．き裂伝ぱ経路は結晶粒構成に応じて屈曲や分岐があり，き裂伝ぱ速度の局所的な変動に対応していた．T試験片の結晶粒構成とき裂形状を模擬した2次元モデルに対して有限要素解析を実施し，き裂パスの各部における弾性J積分値を算出した．J積分はき裂先端近傍の弾性定数とき裂方位と荷重軸の関係に影響され変化した．前者は結晶粒径と同様のサブミリオーダーの周期で変動し，後者は応力軸とき裂伝ぱ方向のなす角が直角から大きく離れる点でスポット的に低下することが明らかになった．き裂伝ぱ速度の一時増加する部位では，J積分も高い値であり，J-da/dN関係はある程度よい相関を示した．ただし，なお結晶粒界き裂は粒内き裂より高いき裂伝ぱ速度を示し，両者でき裂伝ぱ抵抗が異なるものと推察された．

概要 （英文）

High temperature fatigue crack propagation tests are carried out on L and T specimens of a Nickel-based directionally solidified (DS) superalloy, where the DS axis is parallel to the load axis in the L specimens, while the DS, load, and crack propagation axes are set to cross at right angles in the T specimens. There are zigzag bends and crack branches on the crack propagation paths, where the crack propagation rate shows impermanent fluctuation. In order to obtain the J-integral values for various crack sizes and shapes, finite element analysises are carried out on 2-dimentional models simulated the grain configuration and the crack shape of the T specimens. J-integral is affected by two factors, they are the elastic compliance nearby the crack tip and the angle between the crack tip and load axis. The former causes the sub-mm order of fluctuation in J-integral, and the latter 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 J-integral, of where the impermanent increase of crack propagation has been observed, shows higher value than those in the other part. So that, the relationship between the J-integral and the crack propagation rate shows a good correlation to a certain extent. However the intergranular crack propagation rate is higher than that in transgranular one nevertheless, and it supposed to be caused by the difference in crack propagation resistance.

報告者

キーワード