DEFORMATION-BEHAVIOR OF IRRADIATED ZR-2.5NB PRESSURE TUBE MATERIAL

A study of the deformation behavior of irradiated highly textured Zr-2.5Nb pressure tube material in the temperature range of 30-degrees-C to 300-degrees-C was undertaken to understand better the mechanism for the deterioration of the fracture toughness with neutron irradiation. Strain localization behavior, believed to be a main contributor to reduced toughness, was observed in irradiated transverse tensile specimens at temperatures greater than 100-degrees-C. The strain localization behavior was found to occur by the cooperative twinning of the highly textured grains of the material, resulting in a local softening of the material, where the flow then localizes. It is believed that the effect of the irradiation is to favor twinning at the expense of slip in the early stages of deformation. This effect becomes more pronounced at higher temperature, thus leading to the high-temperature strain localization behavior of the material. A limited amount of dislocation channeling was also observed; however, it is not considered to have a major role in the strain localization behavior of the material. Contrary to previous reports on irradiated zirconium alloys, static strain aging is observed in the irradiated material in the temperature range of 150-degrees-C to 300-degrees-C.