Correlation between defect structures and hardness in tantalum irradiated by heavy ions

Pure tantalum specimens were irradiated with 2.4 MeV Cu2+ ions up to 3 dpa at temperatures between room temperature and 1073 K. Transmission electron microscope (TEM) observation and micro-indentation tests were carried out to correlate the microstructure and the hardness. Significant radiation hardening occurred at temperature ranging from 673 to 873 K. Isochronal annealing of a specimen irradiated at room temperature up to a dose of 0.3 dpa resulted in a rapid increase in hardening between 573 and 673 K and continued to increase up to 873 K. The microstructure showed that the formation of small defect clusters is the major reason for both the radiation hardening and the radiation-anneal hardening.