Ni基超合金の微小き裂伝ぱ特性

抄録

Rotating bending fatigue tests were carried out for Inconel 718 at room temperature to investigate the growth characteristics of a small crack. It was found that : (1) The crack initiated at the grain boundary and then propagated as a transgranular crack. (2) When the stress level was higher than the fatigue limit, the fatigue life was mainly controlled by the growth life of a crack smaller than 1mm. (3) The fatigue limit was a limiting stress for the crack propagation. (4) At low stress levels (σ_a/σ_0.2<0.5, σ_a : stress amplitude, σ_0.2 : 0.2% proof stress), the crack growth rate was determined by the stress intensity factor range ΔK ; and at high stress levels (σ_a/σ_0.2>0.6), it was determined by the small crack growth law.