Evolution of dislocation loops and effect of annealing temperature on hydrogen-ion-implanted Fe-based binary alloys

Abstract

Reduced activation ferritic/martensitic (RAFM) steels have been considered as a family of prime candidate structural materials for fusion reactors due to low radioactivity and good resistance to irradiation swelling. Various types of defects such as dislocation loops can form in these materials during irradiation. Effects of alloying elements in iron on the formation and migration of dislocation loops have been widely investigated. However, most studies dealt with interstitial-type dislocation loops in iron alloys, while very few focused on vacancy-type dislocation loops. Previous high voltage electron microscope (HVEM) studies from the authors' group have shown that interstitial loops are fully eliminated in hydrogen-ion-implanted α-Fe at 500 ℃, only vacancy loops remain and can achieve up to 100 nm in size. The addition of Ni in α-Fe can reduce the formation temperature of vacancy-type dislocation loops (<i>T</i>_c) to ~450 ℃, while the addition of Cr can increase the temperature to above 600 ℃. However, these experiments are usually difficult to perform due to the scarce resource of HVEM facilities. In this work, in-situ observations by conventional transmission electron microscope (CTEM, 200 kV) are systematically carried out on the hydrogen-ion-implanted α-Fe and Fe-based binary alloys (Fe-3wt.%Cr, Fe-1.4wt.%Ni and Fe-1.4wt.%Mn). The evolutions of morphology and average size of dislocation loops under different annealing temperatures are investigated. The formation temperatures of vacancy-type dislocation loops are determined from the change of average loop size with annealing temperature. The results are consistent with previous studies by HVEM. The effect of Mn atoms in α-Fe is similar to that of Cr atoms, which leads to <i>T</i>_c increase, and the addition of Ni in α-Fe can reduce <i>T</i>_c. Furthermore, the results of D thermal desorption spectrum analysis show that <i>T</i>_c is affected by the binding and release process of hydrogen isotopes to vacancies in α-Fe. Alloying element Ni promotes the binding and release of hydrogen isotopes to vacancies, which leads to<i> T</i>_c decrease. Cr and Mn inhibit the binding and release of hydrogen isotopes to vacancies, causing <i> T</i>_c to increase.