Positron Annihilation Lifetime Spectroscopy Investigation of Thermal Aging Effect for the Mechanical Properties of Hydrogen-Absorbed Tantalum

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 & 15 vacancies were generated after aging at and above 200 degrees C, and vacancy-11 clusters were generated in 3 and 6h-charged specimens atter aging at 300 degrees C. The loss of ductility in Ta and crack generation were observed by conducting tensile tests in 6 h H-charged specimens after aging at 200 degrees C for 2000 h and in 3 and 6 h H-charged specimens aged at 300 degrees C 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 and vacancy cluster generated by dissolved H during thermal aging. And it was considered that the ductility loss was caused by acceleration of crack propagation by vacancy cluster connection and the local aggregation of hydrogen induced by vacancy-H generation.