High Energy Proton Irradiation of Pure Titanium
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High Energy Proton Irradiation of Pure Titanium Teresa Leguey, Claude Bailat, Nadine Baluc and Max Victoria Centre of Research in Plasma Physics, Association EURATOM-Swiss Confederation, Swiss Federal Institute of Technology - Lausanne, 5232 Villigen-PSI, OVGA/6, Switzerland. ABSTRACT Polycrystalline specimens of hcp pure titanium have been irradiated at 300-320 K with 590 MeV protons to doses ranging between 10-3 and 3x10-2 dpa. Combination of tensile deformation experiments and transmission electron microscopy observations revealed that irradiation produces slight hardening of the material, related to the irradiation-induced formation of defect clusters, but not significant loss of ductility. Plastic deformation of irradiated titanium is homogeneous. It occurs via propagation of dislocations through a cloud of defect clusters, leading to their annihilation and the formation of a cellular dislocation structure together with twins. This mechanical behavior is similar to what was previously observed for pure fcc metals, the formation of twins being however intrinsic to deformation of hcp titanium. INTRODUCTION During the past ten years, a number of investigations of radiation damage effects have been performed on fcc and bcc pure metals, showing significant differences in the defect accumulation rate and the dose dependence of the hardening between these two structures (for a review, see for instance [1]). In order to complement such investigations and in order to allow future comparison with titanium-base alloys that have been selected as candidate structural materials for fusion reactors, a study of the mechanical behavior and microstructure changes of hcp pure titanium under irradiation has been undertaken. Preliminary results are presented below. EXPERIMENTAL Tensile flat specimens of 8 mm in gauge length and 2.5 mm in width have been prepared from polycrystalline cold rolled foils, 0.5 mm thick, of pure titanium (99.999%). The tensile axis was chosen parallel to the rolling direction. The specimens were mechanically polished to get a mirror surface to an approximate thickness of about 300 µm. They were then annealed in vacuum at 973 K for 5 hours. The final grain size was about 80 µm. Series of specimens were irradiated in the PIREX (Proton Irradiation Experiment) facility, at the Paul Scherrer Institute, with 590 MeV protons. These irradiations were performed at 300320 K to doses ranging between 10-3 and 10-1 dpa. The damage rate was approximately 10-7 dpa.s-1. The as-annealed and irradiated tensile specimens were deformed at ambient temperature by using a computer-controlled universal testing machine. The strain rate was about 2x10-4 s-1. Deformation experiments were performed up to fracture. Texture analysis was performed using optical microscopy (OM) and scanning electron microscopy (SEM), while the defects associated with deformation and/or irradiation were imaged in transmission electron microscopy (TEM), with a JEOL 2010 microscope operating at 200 kV, by using the bright/dark field and weak beam techniqu
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