Factors Controlling Irradiation Hardening of Iron-Copper Model Alloy

The factors controlling irradiation hardening and their contributions to the hardening in electron irradiated pure-iron and Fe-0.15 mass%Cu alloy were determined by means of post-irradiation annealing experiments, such as hardness measurements, positron annihilation spectroscopy (PAS) measurements, transmission electron microscope (TEM) observations and three dimensional atom probe (3DAP) analyses. In pure-iron, almost complete recovering of the hardness was observed after the annealing to 773 K, which was accompanied by disappearing of the interstitial type dislocation loops (I-loops) that were observed in as-irradiated specimen. In contrast, the hardening of Fe-0.15 mass%Cu alloy recovered in a two-step mode; about a half of the hardening recovered by the 773 K annealing, and a complete recovery was observed after annealing to 973 K. Most of the I-loops observed in as-irradiated specimen again disappeared after the annealing to 773 K. These clearly show that the I-loops are one of the main factors controlling irradiation hardening in iron-copper alloy. The residual hardening in the Fe-0.15 mass%Cu alloy after the annealing to 773 K, which is about a half of the irradiation hardening, was attributed to the copper-rich precipitates (CRP) through the direct observation by 3DAP analysis. PAS measurements revealed the disagreement between the recovery behaviors of the hardness and lifetime parameters. Based on the quantitative data analysis, it was concluded that the factor controlling the irradiation hardening of pure-iron is the I-loops, and those in Fe-0.15 mass%Cu alloy are both the I-loops and CRP of which the contributions to the hardening are almost same.