Vacancy-type defects and hardness of helium implanted CLAM steel studied by positron-annihilation spectroscopy and nano-indentation technique

China Low Activation Martensitic (CLAM) steel was implanted with helium up to 1e + 16/cm2 at 300–873 K using 140 keV helium ions. Vacancy-type defects induced by implantation were investigated with positron beam Doppler broadening technique, and then nano-hardness measurements were performed to investigate helium-induced hardening effect. He implantation produced a large number of vacancy-type defects in CLAM steel, and the concentration of vacancy-type defects decreased with increasing temperature. Vacancy–helium complexes were main defects at different temperatures. Irradiation induced hardening was observed at all irradiation temperatures, and the peak value of hardness was at 473 K. The result suggested that both vacancy–helium complexes and helium bubbles had contribution to irradiation induced hardening. The decomposition and annihilation of irradiation-induced defects became more and more significant with increasing temperature, which induced the increment of hardness became more and more small.

► Helium implantation is performed to CLAM steel at different temperatures.
► Positron annihilation is used to investigate vacancy-type defects.
► Nano-hardness is investigated to study irradiation induced hardening.
► Vacancy–helium complexes are main defects after implantation.
► Both helium–vacancy clusters and helium bubbles contribute to hardening.