Papers by Keyword: Irradiation Embrittlement

Abstract: Tungsten (W) is a principal candidate as target material because of its high density and extremely high melting point. W inherently has a critical disadvantage of its brittleness at around room temperature (low temperature brittleness), recrystallization embrittlement, and irradiation embrittlement. TFGR (Toughened, Fine Grained, Recrystallized) W-1.1%TiC has been considered as a realized solution to the embrittlement problems. We started to fabricate TFGR W-1.1%TiC in 2016 under collaboration between KEK and Metal Technology Co. LTD (MTC). The TFGR W-1.1%TiC samples were successfully fabricated in June, 2018. As a result, the specimen showed slight bend ductility and 2.6 GPa of fracture strength.

Abstract: Very high cycle fatigue degradation of type 316L austenitic stainless steel, which is used as the structural material of neutron spallation sources under intensive neutron irradiation environment, is investigated by using an ultrasonic fatigue testing machine. The strain rate imposed on the structure of neutron spallation source is almost equivalent to that produced in the testing machine. The temperature on the surface was controlled by the air-cooling. The effect of strain rate on the fatigue strength is recognized to increase the fatigue limit.

Abstract: Fracture of ferritic reactor pressure vessel steels is determined by temperature and specimen size. In low temperature fracture occurs by cleavage, with elevation of temperature and decrease of specimen size the ratio of ductile tearing prior to cleavage increases and, in the end, fracture will have a ductile character. There is a temperature interval where both fracture mechanisms are present. Hypothesis of the traditional (global) assessment method has been that the shift of the fracture toughness reference curves due to neutron irradiation is equal with the shift of the ductile-to-brittle transition temperature measured by the Charpy impact test. Local assessment approaches based on the „weakest link” statistical theory recommend the direct measurement of fracture mechanics parameters to structural integrity evaluation. The paper describes the main features of both global and local approaches, analyzing the micro structural aspects of the most known micromechanical models of local approach and drawing conclusions concerning their applicability.