The Study On The Influence Of Cold Deformation And Heat Treatment On The Irradiation Hardening Resistance Property Of V-5Cr-5Ti Alloys

Because of the low activation,excellent high-temperature strength and compatibility with liquid lithium,vanadium alloys have been considered as one of the candidate structural materials for the blanket of fusion reactors.Significant irradiation hardening occurs in vanadium alloys under irradiation at low temperatures(<400 ℃),accompanying the loss of ductility and the increase of ductile-brittle transition temperature(DBTT).Therefore,irradiation hardening/embrittle at low temperature is a key issue for the application of vanadium alloys as the structure materials in the advanced nuclear energy system.By fabricating with different content of cold deformation and heating treatment processes,the grain boundaries and dislocation density can be modified effectively.Grain boundaries,dislocations can effectively trap point defects produced during irradiation,affect the evolution of irradiation defects and thus,have an impact on the irradiation hardening/embrittlement.In this study,V-5Cr-5Ti vanadium alloys with different cold deformation amounts(40,60 and 80%)followed by heat treatment(1273 K)were irradiated by 337 Me V Fe ions at 100 ℃ in HIRFL(Heavy Ion Research Facility in Lanzhou).The results of microstructure and hardness tests show that the proportion of fine broken grains increased with the increase of cold deformation amount.Meanwhile,the average grain size decreased and the dislocation density within grains decreases firstly and then increases,which resulted in the increment of hardness.After annealing,the proportion of large grains disappeared accompanying the growth of the fine broken grains and the distribution of grain size became more uniform.The dislocation density and hardness also decreased.The synergistic effect between dislocation and grain boundary is observed during microstructure evolution at the high cold rolling amount.After irradiated by high-energy Fe ions,the hardness of all samples increased significantly,which indicates the occurrence of irradiation hardening.The hardness increased rapidly as the dose increased,and tended to saturate at higher dose.The calculated sink strength of grain boundary and dislocation and the distribution of irradiation defects indicates that the evolution of irradiation defects was mainly influenced by dislocation lines in cold-rolled samples while dislocation lines and grain boundaries affected the evolution of irradiation defects together in annealed samples.TEM results show that the irradiation defects in the irradiated samples are mainly the irradiation induced dislocation loops.The average size of the irradiation dislocation loops showed little difference in the cold-rolled and annealed samples,but the number density of the dislocation loops in the cold-rolled samples was lower than that in the annealed samples,which is mainly ascribed to the effect of initial microstructure on the evolution of irradiation defects.