インコネル600の85°C, 50%NaOH溶液中における腐食疲労き裂伝播におよぼす電位の影響

Abstract

A study has been made of corrosion fatigue crack growth for Inconel 600 solution-annealed at 1100°C for 0.5 h in 85°C 50%NaOH solution with a frequency of 1.1 cycle per minute. The effect of potential on the corrosion fatigue crack growth rate (da⁄dN) as a function of ΔK was examined and the fracture surfaces were observed. The results obtained are as follows:(1) The crack growth rate and the cracking mode were affected by the applied potentials in the anodic polarization curve. The value of da⁄dN was arranged in the following order of the observed potentials: secondary passive region>corrosion potential>primary active region>primary passive region.(2) Intergranular cracking took place at a secondary passive potential (−0.04 V vs SCE) which gave a maximum crack growth rate. Transgranular cracking with fatigue striations occurred at the other potentials.(3) The variation in current with the alternating loading was observed at the potentials where transgranular cracking occurred, whereas no appreciable correlation between current and cyclic loading was shown at a potential of −0.04 V where the intergranular mode cracking occurred.(4) It is pointed out to be helpful in studying the influence of applied potential on the acceleated rate of cracking at the crack tip by the “crack-tip opening displacement” estimated from the stress intensity, as the major mechanical condition.