Mechanical properties of pure tantalum after 800 MeV proton irradiation

Specimens prepared from a spent tantalum target of the pulsed spallation source ISIS, irradiated with 800 MeV proton to a maximum fluence of 1.7×1025 p m−2 at temperatures lower than 200 °C, were investigated by micro-hardness, three-point bending and tensile tests at room temperature (RT) and at 250 °C. All three types of mechanical measurements consistently showed irradiation hardening. Furthermore, the tensile tests showed that the increase in yield strength is accompanied by a reduction of the strain-to-necking at both test temperatures. For instance, at RT, the strain-to-necking was reduced by irradiation from initially 30% to about 10%. This drop in ductility occurred at doses below 0.6 dpa, whereas afterwards the strain-to-necking remained constant up to the maximum dose of about 11 dpa. The results of tests at 250 °C were similar to those at RT. SEM investigation revealed typical ductile fracture surfaces even for the highest doses. Optical micrography after bending tests showed no cracks even after bending of a 2 mm thick specimen end to end, indicating that pure Ta retained very high ductility after proton irradiation.