A STUDY OF MECHANICAL PROPERTIES OF IRRADIATED TITANIUM AND ITS ALLOYS AT LOW TEMPERATURES

Abstract

The present work attempts to study the effects of irradiation and deformation temperature on the mechanical properties of polycrystalline pure titanium (99.994 %). The specimens were irradiated by electron beam of energies ranging from 8-18 MeV at 300 K. The irradiated and unirradiated specimens were deformed using Universal Testing Machine in the temperature range 300-100 K at a strain rate of 1.2  10-3 /sec. A comparison between stress strain curves of unirradiated/ irradiated specimens recorded through the attached machine at room temperature, was carried out. The yield stress and ultimate tensile stress of irradiated specimens were found to be higher than that of unirradiated ones however the ductility was found to decrease. The changes in tensile parameters became more pronounced with increase of irradiation energy and decrease of test temperature. The stress relaxation tests were also conducted to observe stress relaxation behavior of the material at a certain fixed load. The stress relaxation rate was found to be lower in irradiated specimens than that of unirradiated ones lowering of test temperature and enhancing of irradiation energy. The activation parameters of stress relaxation like activation energy and activation volume were also analyzed from the relaxation tests. The activation energy was found to increase with decrease of test temperature and with increase of incident irradiation energy. The analysis of activation energy (U0) and activation volume (Vσ) suggests that the initial plastic deformation in irradiated titanium specimens is controlled by the interaction of dislocations with irradiation induced defects while this advances into dislocation-dislocation intersection as the deformation i proceeds which seem to control the rate process in irradiated polycrystalline titanium. Scanning electron microscope micrographs of the fractured surfaces show a combination of ductile and cleavage fractures, corresponding to different values of irradiation energy and test temperature.