Effect of irradiation temperature on the microstructure and hardness of W-0.3Cr alloy after irradiation with 6.4 MeV Fe ions

• The diffraction peaks shift to lower 2θ at all temperatures (773–1273 K), confirming irradiation-induced lattice swelling due to defects. • An increase in irradiation temperature resulted in the growth of large dislocation loops and a slight reduction in the number density of dislocation loops. • The precipitation of Cr was absent in the sample after irradiation at 773 K but was clearly observed in the samples irradiated at 1073 and 1273 K. • Irradiation hardening was observed at all temperatures. The hardness change, estimated with the dispersion barrier hardening model considering dislocation loops and Cr precipitates, was much higher than the nanoindentation results due to Cr atom depletion from precipitation. The W-0.3 at.% Cr alloy samples were irradiated with 6.4 MeV Fe ions at 773, 1073 and 1273 K, and the damage peak was 0.26 dpa. The evolution of the microstructure, defects, and hardness was investigated using grazing-incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM) and nanoindentation tests. The GIXRD results showed that diffraction peaks shifted towards lower 2θ values, indicating that lattice swelling was caused by irradiation-induced defects after irradiation at elevated temperatures. According to the TEM observations, the size of the dislocation loops remained nearly constant, while their number density decreased with an increase in irradiation temperature. The precipitation of Cr was not observed in the W-0.3Cr alloy after irradiation at 773 K. In contrast, it was significant in the samples irradiated at temperatures of 1073 and 1273 K, showing increases in both the size and number density of the precipitates. Irradiation hardening was observed in all samples, primarily attributed to the presence of dislocation loops. The hardness change was estimated with the dispersion barrier hardening model by taking into account the contributions of dislocation loops and Cr precipitates. The values evaluated with the model were significantly larger than those obtained with the nanoindentation tests. This difference was ascribed to the depletion of solute Cr atoms from the W matrix by precipitation.