Transgranular Stress Corrosion Cracking Mechanism of Alloy 690 in Simulated PWR Primary Water

摘要

Alloy 690 showed transgranular cracking as well asintergranular cracking in simulated PWR primary water.The transgranular stress corrosion cracking mechanismof Alloy 690 has been studied based on crystallographicrelationships of internal oxides with substrate andcracking paths in simulated PWR primary water. Internaloxides near crack tips were observed on {111} and {200}close packed planes with wide lattice spacing and havesemi coherency with the substrate. Internal oxide on the{111} plane was larger and more well developed thanthat on the {200} plane because of wider lattice spacing.A disc-shaped internal oxide was identified on the {111}plane that was about 10 nm thick and 30 nm long. Theobtained diffraction pattern showed that transgranularcracks propagated along the {111} and {200} planes. Theratio of transgranular cracking over intergranularcracking appears to be determined by the degree of coldwork. The transgranular cracking mechanism of Alloy690 was proposed in simulated PWR primary water.