Effect of electron beam irradiation on fracture and fatigue characteristics of TZM

TZM is one the of suitable materials for the first wall of a fusion reactor because of its high temperature strength, high melting point and high heat conductivity. However, it is necessary to investigate the effect of high heat flux irradiation from the plasma on the mechanical properties of TZM. In this report, we used an electron beam as a source of high heat flux to simulate plasma disruption load. First, the electron beam irradiated TZM specimens and then tensile, fatigue and fracture toughness tests were carried out at room temperature and 250deg C. These mechanical properties of TZM gradually decrease along with the increase of beam power. Once TZM's surface was, however, melted and recrystallized, the mechanical properties at room temperature abruptly degraded to some extent. Microscopic observation was also made on the section including the melted layer and the fracture surface. The melted layer often included blowholes near the specimen surface and some grain boundaries seemed to be separated. Fracture toughness at 250deg C was much higher than at room temperature. It means that the ductile brittle transition temperature of TZM may exist between 250deg C and room temperature. (orig.)