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 x 10(25) p m(-2) at temperatures lower than 200 degreesC, were investigated by microhardness, three-point bending and tensile tests at room temperature (RT) and at 250 degreesC. 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 I I dpa. The results of tests at 250 degreesC 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. (C) 2001 Elsevier Science B.V. All rights reserved.