Fracture Toughness and Stress Corrosion Resistance of U-0.75 wt.% Ti

As a consequence of the several failures of U-0.75 wt% Ti circumferentially grooved machined bars stressed at lower than normal ambient temperatures, an intensive fracture. toughness study of the U-0.75 wt% Ti material was carried out. The objective of the study was to determine the effect of heat treatment, microstructure, hardness, mechanical properties and test temperature on fracture toughness. Fracture toughness measurements in the temperature range of -73 deg C to +38 deg C were made for the alloy processed by (1) alpha extrusion, gamma vacuum solution treatment, directionally quenching in H2O, aging; (2) gamma rolling, gamma solution treatment in molten salt, plunge quenching in oil, aging; (3) solution treatment in vacuum for the material processed in (2), directionally quenching in H20 and re-aging. Two types of fracture toughness specimens were considered. Based on preliminary test data, a slow-bend precracked Charpy specimen was selected for final measurements. Data obtained was compared with the meager fracture toughness data for the alloy reported in the literature. Based on these data, a minimum fracture toughness requirement at -46 deg C as recommended. (MM)