Comparative investigation of temperature-dependent defect evolution and irradiation hardening in CVD and ITER-like tungsten

Chemical vapor deposited tungsten (CVD-W) is known for its high thermal stability of the microstructure and lower susceptibility to deuterium-induced blistering compared to ITER-like W (IL-W). However, it remains unclear whether these advantages extend to displacement damage tolerance. To address this, CVD-W and ITER-like tungsten (IL-W) were irradiated with 6 MeV copper ions up to 0.6 dpa at room temperature (RT), 773 K, and 973 K. Transmission electron microscopy, defect statistics, and nano-indentation revealed comparable damage accumulation and irradiation hardening in both materials across all investigated temperatures. At RT, both materials exhibited dense dislocation networks and loops, together with very sparsely distributed voids, resulting in comparable increases in hardness. At elevated temperatures, these networks disappeared, giving way to dislocation loop strings and dislocation lines, along with an increased density of voids, accompanied by further irradiation hardening. The dispersed barrier hardening model analysis indicates that the dominant contribution to irradiation hardening transitions from dislocation structures at RT to voids at elevated temperatures. In addition, differences in dislocation morphology and nature were observed between the two materials. Displacement damage defects in CVD-W exhibited higher mobility than in IL-W, as evidenced by an expanded damage layer, a higher degree of dislocation loop ordering into one-dimensional strings, a larger fraction of glissile 1/2<111> dislocation loops, and a greater proportion of loops exceeding 10 nm at ≥ 773 K, mainly owing to its lower impurity content. This further supports void-dominated hardening at elevated temperatures, as different dislocation morphologies observed at elevated temperatures had minimal impact on the overall hardening. These findings provide valuable insights into the irradiation response of CVD-W under fusion-relevant conditions.