多結晶Ni基超合金の微視組織的微小疲労き裂の進展と結晶粒界での停留挙動

抄録

Fatigue crack propagation in a polycrystalline Ni-base superalloy was experimentally investigated. Special focus was put on the effect of grains crystal orientation and grain boundary on fatigue crack propagation, employing bi-crystal, coarse grain, fine grain CT specimens extracted from a directional solidified superalloy, MGA-1400. A series of experiments revealed that trans-granular crack propagation was affected by the primary and secondary crystal orientation of grains, and fundamental mechanism of Stage I cracking along slip planes could be interpreted by the experimental and analytical findings in the single crystal material. It was also found that the grain boundary in the bi-crystal specimen caused the retardation of crack propagation depending on crack propagation modes just after the grain boundary. In case the crack propagated in Stage I manner after the grain boundary, crack retardation became more pronounced due to the Stage I + II cracking.