Nanoindentation has been performed on tungsten, unimplanted and helium-implanted to ~600. appm, at temperatures up to 750. °C. The hardening effect of the damage was 0.90. GPa at 50. °C, but is negligible above 450. °C. The hardness value at a given temperature did not change on re-testing after heating to 750. °C. This suggests that the helium is trapped in small vacancy complexes that are stable to at least 750. °C, but which can be bypassed due to increased dislocation mobility (cross slip or climb) above 450. °C.
Gibson, J. S. K. L., Roberts, S. G., & Armstrong, D. E. J. (2015). High temperature indentation of helium-implanted tungsten. Materials Science and Engineering A, 625, 380–384. https://doi.org/10.1016/j.msea.2014.12.034