Positron annihilation lifetime spectroscopy investigation of thermal aging effect for the mechanical properties of hydrogen-absorbed tantalum

Ishijima, Yasuhiro ; Yokoyama, Kenichi*; Ueno, Fumiyoshi  ; Abe, Hitoshi 

The effect of thermal aging on the behavior of vacancy-hydrogen (H) cluster generation and the mechanical properties of tantalum (Ta) were investigated by positron annihilation lifetime spectroscopy (PALS) and tensile tests. Based on the PALS results, vacancy clusters that included 8-15 vacancies were generated after aging at and above 200C, and vacancy-H clusters were generated in 3 and 6 h-charged specimens after aging at 300C. The loss of ductility in Ta and crack generation were observed by conducting tensile tests in 6 h H-charged specimens after aging at 200C for 2000 h and in 3 and 6 h H-charged specimens aged at 300C for 2000 h. The reduction of ductility due to thermal aging of Ta was also observed under these thermal aging conditions. These results suggested that vacancy-H cluster generated by dissolved H during thermal aging induced the ductility loss by reducing the dislocation migration during deformation.