Studies On The Irradiation Damage In Iron Based Binary Alloys And The Behavior Of Gas Bubbles Under Electron Irradiation

A simple irradiation experimental method namely the ion irradiation covered with copper nets was used to investigate the mutual interaction of irradiation-induced point defects,solute atoms and grain boundaries in Fe-Al model alloy after helium irradiation at different temperatures.Results showed that the concentration of A1 in the irradiated region is higher than that in the non-irradiated region.The composition changing is different at two sides of the grain boundary and trends to decrease as the irradiation temperature increases.After irradiation at 300℃ and 400℃,comparing with the non-irradiated region,the Al depletion at the GB is not obvious in the irradiated regions.The experimental datum could be explained by the flow of irradiation-induced point defects and crystal orientation.For comparison,in-situ electron irradiation was conducted in a high voltage electron microscope(HVEM),and the results are consistent well with that of the helium ion irradiation.The synergy effect of hydrogen and point defects on Cr precipitation was studied in Fe-Cr model alloy.Fe-10at.%Cr ferritic model alloy pre-implanted with hydrogen ions was electron-irradiated in a high voltage electron microscope(HVEM)at the temperature ranging from 300 ℃ to 600 ℃.Streaks were observed in the diffraction patterns in the model alloy after electron irradiation at 450-550 ℃and explained reasonably by shape effect.The analysis of transmission electron microscopy(TEM)reveals that the observed streaks are induced by a kind of needle-like precipitates with the directions along<100>.The dependence of the length and density of the precipitates on the temperature were studied.In addition,contrast experiments were conducted with pure Fe and Fe-10at.%Cr alloy with and without hydrogen ion implantation,respectively.After electron irradiation,no streak was observed in the hydrogen-implanted pure Fe and Fe-10at.%Cr alloy without the hydrogen implantation.Therefore,it is assumed that the needle-like precipitates could be the complex of Cr and H,which segregate and precipitate along<100>direction.The nature of the dislocation loops formed after annealing from 500 ℃ to 620 ℃ in hydrogen ion implanted Fe-10at.%Cr model alloy was studied by the evolution of loops under in-situ electron irradiation in a high voltage electron microscope(HVEM).It indicated that only interstitial-type loops were observed when annealed at 550 ℃ and below,but vacancy-type loops started to form at the temperature higher than 600 ℃.According to the previous study of our group,the presence of chromium element made the formation temperature of vacancy-type loops higher than that in pure iron.The effect of alloying elements on the formation temperature of the vacancy-type loops was discussed.In addition,the interstitial-type dislocation loops formed at the annealing temperature of 550 ℃ and below in hydrogen-ion implanted Fe-10at.%Cr alloy were examined based on dislocation loop maps and g·b=0 invisibility criteria.The results of characterization showed that after annealing at 400 ℃ and 500 ℃,the proportion of<100>type dislocation loops were 16.48%and 92.78%respectively in hydrogen-ion implanted Fe-10at.%Cr.With the temperature increasing to 550 ℃,all the dislocation loops were of<100>type loops.It indicated that comparing with pure iron,the presence of Cr promoted the transition temperature of dislocation loops from 1/2<111>type to<100>type.Regarding the behavior of gas bubbles under electron irradiation,the TEM was used to in-situ observe and investigate the anomalous heat-releasing phenomenon from inert gas bubbles in aluminum induced by electron Irradiation.The results showed that under 200 keV electron irradiation,three kinds of inert gas bubbles all coalesced,grew up and busted respectively.Finally,lots of nanoscale black dots were produced inside them.At the same time,the diffraction patterns changed from single crystal diffraction spots to polycrystalline diffraction rings.Certain kind of heat release should happen leading to poly-crystallization of aluminum.With the fluence of gas ion implantation increasing,it required less irradiation time for the poly-crystallization of aluminum.However,helium bubbles and its mixed bubbles with argon were irradiated by 80 keV and 200 keV electrons respectively,no diffraction rings were observed after irradiation,which was related to the energy of the electron beam and pressure of gas bubbles separately.