| Nuclear structural materials are widely used in the internal structure of fission and fusion reactors due to their excellent radiation resistance,corrosion resistance,heat resistance and mechanical properties.The aging and embrittlement of nuclear structural materials often occur under the environment of high temperature,hydrogen and high-pass neutron irradiation.However,the mechanisms and microscopic mechanisms of these changes,as well as the understanding of hydrogen/helium interactions with defects,remain unclear.At present,there are already technical means to observe the micro-defects of nano-level precipitates and open volume in materials,among which the positron annihilation technology is very sensitive to micro-defects.In this paper,type-316 austenitic stainless steel and Fe9 Cr alloy were used as research objects to study the thermal evolution of micro-defects and the behavior of hydrogen/helium.This is of great significance for further understanding the evolution of micro-defects and the behavior of hydrogen/helium.The main contents and conclusions of this paper are as follows:(1)Thermal evolution of micro-defects and hardness in type-316 austenitic stainless steel was investigated.The results reveal that the vacancy defects gradually recover with the increase of annealing temperature.When the annealing temperature is lower than 673 K,the change in hardness remains almost unchanged.Because this temperature range is dominated by the recovery of mono-vacancy defects,the recovery of mono-vacancies has little effect on hardness.In annealing temperature range of 673 K to 823 K,dislocations aggregation and formation of dislocation networks results in a slight rise in hardness.From 873 K to 1173 K,gradual recovery of dislocations and generation of large precipitates resulted that hardness in general decreased but fluctuated within a small range.Subsequently,the precipitates became smaller and melted away mostly.After annealing at 1173 K,the remaining dislocation defects continue recovering and hardness continues decreasing.After annealing at 1373 K,it exits no defects basically in the specimen and the hardness does not change significantly.(2)The interaction between hydrogen and defects in austenitic 316 stainless steel was investigated.The longer the hydrogen filling time,the higher the vacancy defect concentration in the sample.In type-316 austenitic stainless steel with different deformation,hydrogen plasma injected with low energy and high dose diffuses into theinterior from the surface of the sample,and new vacancy defects are generated in the interior.The dislocation in the interior of the sample inhibits the phenomenon of hydrogen-induced radiation swelling.This is due to the combination of hydrogen and dislocation,forming a complex of dislocation and hydrogen,hindering the migration and growth of hydrogen.(3)As the main body of low activation martensitic steel and steel materials,Fe9 Cr alloy was study about micro-defects and helium condition after annealing,quenching and deformation separately,then through 50 keV helium ion irradiation: from 380 K to640 K and from 640 K to 1010 K,helium releases from single vacancy(HenV)and dislocation(HenD),respectively.From 1010 K to 1200 K,helium release was caused by Fe9 Cr by the BBC the FCC phase shift.From 1200 K to 1420 K,helium releases from HenVm clusters and helium bubbles.The evolution of HenVm cluster in the annealed samples irradiated by helium ions was investigated by using the slow beam at the peak point of thermal desorption.With the increase of temperature,a large number of vacancy defects were recovered.650K-840 K,the HenVm cluster in the sample gradually migrated and aggregated,the net vacancy generation rate was greater than zero,the density of internal open space defects increased.From 840 K to 1160 K,HenVm clusters in the material move from the shallow region of the material to the deeper region of the material.1160 K-1360 K,the deeper HenVm clusters gradually move towards the shallow layer. |
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