Effect Of Ion Irradiation On The Microstructure And Properties Of W-ZrO₂ Alloy

Controlled fusion energy has become one of the most promising alternative energy sources due to its low risk and high energy efficiency.The performance and service life of plasma facing materials are the basic guarantee for the stable operation of nuclear fusion reactors.Tungsten alloys are the most promising candidates for plasma facing materials due to their high melting point,high thermal conductivity,high sputtering valve energy,low vapor pressure and low H/He retention.However,the shortcomings of pure tungsten with high brittleness,high ductile brittle transition temperature and low recrystallization temperature limit its application in nuclear fusion reactors.The service environment of plasma facing materials is harsh,and they are subjected to high thermal load and strong particle irradiation for a long time,and their performance degradation is serious.It is important to carry out the research on the anti-irradiation performance of tungsten alloys and elucidate the mechanism of irradiation damage to realize the application of tungsten alloys in nuclear fusion reactors.In this work,pure tungsten and W-ZrO₂ alloys prepared by azeotropic distillation method of powder making,hot press sintering of samples combined with spin-forging thermal processing were selected for the study,and the samples were irradiated at 700°C using 3.0 Me V carbon ions at irradiation doses of 0.1 dpa,0.5 dpa,1.0 dpa and 2.0 dpa.The microstructural changes,evolution of dislocation loops and cavity defects,surface morphology and surface hardness in the samples due to irradiation were investigated in depth.Simulation of the effect of carbon ion irradiation on W and ZrO₂ reveals that:the blocking principal of tungsten is dominated by electron blocking at incident ion energies higher than 0.5 Me V,and decreases with increasing energy.The energy loss of incident ions is dominated by ionization loss,which shows the formation of a large number of electron holes and reduces the evolution of dislocation loops and layer dislocations,indicating that W has good resistance to irradiation.The peak ion concentration in the alloy increases with increasing ion energy.When the incident ion energy is certain,the retention position of ions in the sample is concentrated at a certain depth,and the irradiation damage accumulates as the irradiation dose increases.Comparing the two materials,it is found that the irradiation damage of ZrO₂ grains is higher than that of W under the same irradiation conditions,so the addition of ZrO₂ reinforced phase should control the content and size to avoid the negative impact of ZrO₂ on the overall irradiation resistance of the material due to irradiation.The microstructure of tungsten and W-ZrO₂ alloys was altered by C ion irradiation at 700°C,and a large number of irradiation defects,including point defects,vacancies,dislocation loops,and voids,were generated in the grains.As the irradiation dose increases,the irradiation damage accumulates,and the number density and diameter of dislocation rings and voids gradually increase.When the irradiation dose increased from0.1 dpa to 2.0 dpa,the dislocation loop diameters in tungsten and W-ZrO₂ alloys increased from 2.9 nm and 2.6 nm to 4.5 nm and 3.8 nm,respectively,and the dislocation loop number densities increased from 1.3×10²³/m³ and 1.2×10²³/m³ to 1.8×10²³/m³ and1.6×10²³/m³,respectively.Under the same irradiation conditions,the number density and diameter of dislocation loops and cavities in W-ZrO₂ alloy are smaller than those in W.The dislocation ring diameter increment in W is 1.6 nm,which is 1.3 times larger than that in W-ZrO₂ alloy.The presence of cavities causes swelling of the material,and the W-ZrO₂ alloy exhibits better resistance to swelling than tungsten,with the swelling rate ranging from 0.1%to 0.15%,which is 61%of that of W.The surface hardness of the irradiated samples was measured using a nanoindenter,and the data were processed using the proportional specimen resistance model and the Nix-Gao model to obtain as accurate a surface irradiated layer hardness as possible.The results showed that the irradiation hardening effect on the surface of W and W-ZrO₂alloys was obvious after ion irradiation,and the increase of irradiation dose made the irradiation hardening effect more obvious.The irradiated layer hardnesses of tungsten and W-ZrO₂ alloys were 6.6 GPa,7.4GPa,8.5 GPa,9.3 GPa and 6.4 GPa,7.0 GPa,7.8 GPa,8.5 GPa,respectively,under different irradiation conditions.the irradiated surface hardness of tungsten was 1.3-1.7times that of the unirradiated layer,and the irradiated layer hardness of W-ZrO₂ alloy was only 1.1-1.4 times that of the unirradiated layer.1.1～1.4 times of the unirradiated layer.In comparison,the irradiation hardening effect of the W-ZrO₂ alloy was found to be weaker.The addition of the ZrO₂-reinforced phase refines the grain,increases the grain boundary density,and provides phase boundaries that enhance the absorption annihilation of point defects at the interface in the tungsten alloy,reducing the number of dislocation loops and voids,thereby attenuating the irradiation hardening phenomenon and improving the irradiation resistance of the material.It can be seen that increasing the sink strength of the interface against defects can improve the irradiation resistance of the material.