Irradiation hardening induced by blistering in tungsten due to low-energy high flux hydrogen plasma exposure

In this work, the microstructure evolution in the near-surface of tungsten under hydrogen (H) plasma exposure conditions was observed by means of scanning electron microscopy (SEM), plasma focused ion beam (FIB) and transmission electron microscopy (TEM) techniques. Blisters, with existing dislocations distributed around obviously, were observed beneath the tungsten surface when the exposure temperature was 573 K, which was rarely reported in previous studies. However, H bombardment at 1273 K did not lead to the formation of blister-like microstructures. Correspondingly, irradiation hardening occurred after low temperature exposure, but not after high temperature exposure, according to the Berkovich nano-indentation experiments. In order to characterize the indentation size effect and irradiation hardening behavior of plasma-exposed materials, a mechanistic model was proposed for the hardness-depth relationship. A good agreement between the experimental indentation data and theoretical results revealed that plasma-induced dislocations play a dominant role in determining the increase of hardness for H plasma-exposed tungsten.