Positron beam Doppler broadening spectra and nano-hardness study on helium and hydrogen irradiated RAFM steel

• The main defects of low dose irradiated RAFM steels are (He, H)–V complexes.
• H can decrease vacancy defects by forming H–V complexes.
• H can accelerate the formation of (He, H)–V complexes.
• Hardening induced by helium is obviously larger than that induced by hydrogen.
• Hardening reveals the synergistic effects between He and H irradiation.

The reduced activation martensitic steel was irradiated with 250 keV He2+ to 3000 appm and 130 keV H+ to 15,000 appm alone and in sequence at 450 °C. The S–W curve obtained by the positron beam Doppler broadening spectra reveals that (He, H)–V complexes were induced by irradiation. The S parameters show that the H irradiation can decrease defects by forming H–V complexes. The He irradiation can form He–V complexes and the sequentially implanted H can accelerate the formation of (He, H)–V complexes. Hardening induced by He+H sequential irradiation is greater than that by He or H ion irradiation alone, suggesting synergistic effects of He and H on defects and hardening.