Clarification of crack initiation mechanism under irradiation and fatigue and development of method for detecting and lengthening initiation life by nano-level analysis of surface morphology

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The objective of this study is to clarify the crack initiation mechanism under irradiation and fatigue damages in the reduced activation ferritic steel and its weld, and to develop the index for detecting the crack initiation and the method for lengthening the initiation life.It was clarified that the crack initiation occurred at the prior austenitic grain boundary, the packet boundary, the block boundary, and the inside of the block structure. Most of the crack initiation was observed in the matrix. The irradiation damage induced the shortening of the initiation life. No change of the initiation sites and their ratio occurred due to the irradiation damage.The suppression of the crack growth by the prior austenitic grain boundary was clarified regardless of the irradiation damage. Based on this result, the fatigue crack initiation under the irradiation damage would be suppressed by the optimization of the grain size and the probability of the existence of the grain boundary.