Ｎｉ基超合金の高温疲労き裂伝ぱ特性に及ぼす一方向凝固結晶組織の影響

Abstract

In order to clarify the crack propagation property of Nickel-based directionally solidified superalloy, longitudinal loading (L-type) specimens and transverse loading (T-type) specimens were subjected to the high temperature fatigue crack propagation tests. Fatigue crack propagation rate was correlated fairly well with effective stress intensity factor range ΔKeff, regardless of specimen type (L or T), stress range, and R ratio. In detail, crack propagation rate in T specimen showed eminent fluctuation and it was partially accelerated to 3 to 5 times faster than the average. Detailed observation of specimens revealed that the fluctuation was strongly dependent on the micro-structure along the crack propagation path. Both of transgranular and intergranular crack types were observed on the crack propagation path of T specimen, while that in L specimen showed only the transgranular type. Moreover, transgranular crack showed two different failure planes, they were along {111} or {001} planes, respectively. Since most part of the whole tests were governed by transgranular cracking, they showed mostly the same propagation property. Intergranular crack in T specimen showed much faster propagation than the transgranular crack, and caused eminent fluctuation of propagation rate.