Effect Of Thermal Ageing On Ductile-Brittle Transition Temperature Shift Of Zircaloy-2

Ductile-brittle transition temperature shift and fractographic examination were made on thermal aged zircaloy-2 specimens fracture tested at temperature between -37oC and 230oC, to study the effect of thermal ageing on ductile-brittle transition temperature shift of zircaloy-2. The transition temperature shift of the specimens were tested by Charpy Impact Testing Method. While the fracture surface of the specimens were observed by scanning electron micrography. The original material used in this study was commercial zircaloy-2 rod with diameter of 8 cm. Sectioning was done using cutting machine to make standard Charpy V-notch specimen with dimension of 10 m x 10 mm x 55 mm. After sectioning the specimens were thermal aged with the following steps are- β-quenching at 1030oC during 30 minute then quenched by water, and thermal ageing at 250oC, 450oC and 650oC during 1-2 hour then furnace cooling. The data from Charpy impact test indicated that the ductile-brittle transition temperature of standard specimen (as received specimen) was about -60oC at reference energy of 41 joule. After quenching, the transition temperature of the specimen was shifted to about 79oC By thermal ageing following the quenching, the transition temperature shift was increased up to 190oC. The greater the ageing temperature, the greater the transition temperature of specimen. But at 650oC and 1 h thermal aged specimen, the transition temperature was degreased to 107o. The resulted data from fractographic observation generally show that the type of fracture mode is transgranular dimple fracture. Ageing after quenching is do not change the fracture mode is mixed of dimple and cleavage. But at high temperature testing, the fracture mode is dominantly by dimple. Especially for aged sample at 250oC for 2 hours, at high temperature testing, the fracture mode is dominantly mode is dominantly by intergranular cleavage. (author)