| Nuclear fusion energy is considered to be one of the principal ways to effectively solvethe future energy problem.In actual fusion reaction process,plasma facing materials?PFMs?will have to bear very harsh and wicked environments.Tungsten?W?is considered to be the most promising candidate material for plasma-facing components in fusion devices?ITER and DEMO?for the present reference design,due to the favorable physical properties under high heat and particle fluxes,such as high melting temperature,high thermal conductivity,low thermal expansion coefficient,low sputtering erosion yield,and low tritium retention in radiation environment.However,due to its low-temperature brittleness,recrystallization brittleness,radiation-reduced brittleness and other disadvantages,the present proposed pure tungsten is still far from all the requirements of PFMs.Therefore,it is very important to improve the comprehensive performance through the design of composition,structure and organization in order to reduce the brittleness and improve the anti-irradiation ability of materials.This paper focused on the preparation of W alloy,and the effects of rare earth oxide Sc2O3 on the structure and properties of W matrix composite were studied;on this basis,W–Zr/Sc2O3 composites with different content of Zr were prepared,and the influence of Zr element on the microstructural characteristics and properties of the alloy was also studied,as well as the influence rule on the microscopic structure and properties of W-based materials after composite doping with the alloy element Zr and the rare earth oxides Sc2O3;under the precondition with appropriate amount of Sc2O3,W–ZrC/Sc2O3composites with different content of ZrC were prepared,and the effects of ZrC on the structure and properties of the alloy were studied,as well as the influence rule on the microscopic structure and properties of W-based materials after composite doping with ZrC and Sc2O3 and the damage behavior caused by helium irradiation;the W–Sc2O3/?Zr,ZrC?composites were carried out with deuterium?D?irradiation experiments,and the effects of Sc2O3,Zr,or ZrC addition on D retention in W-based composites were investigated.What's more,exploratory research was also conducted in order to study the effect of He?ion pre-irradiation on D retention in materials with 5 keV after a dose of1í1021 He?/m2 at room temperature?RT?,as well as the influence of the surface heating?523 K?during D2?ion irradiation on D retention;the thermal shock behavior of W–Zr/Sc2O3 composites was investigated by transient electron beam,and the transient thermal shock tests were also carried out on the W–ZrC/Sc2O3 composites by electron beam and laser beam.We also compared the results of the thermal shock behaviors on W–ZrC/Sc2O3 composites under two different energy sources.The main results of the study are as follows:?1?W–Sc2O3 composites with three different contents of Sc2O3?0,0.5vol.%,2vol.%?were successfully prepared via two different techniques:mechanical alloying?MA?followed by hydrogen reduction and SPS,and mechanical wet-milling followed by GPS.By comparison,W–2vol.%Sc2O3 composite had the best comprehensive performance.In the specified range?Sc2O3:02vol.%?,with the increase of Sc2O3 content,the relative density and microhardness of W–Sc2O3 samples increased,while the grain size gradually reduced.The fracture mode of the material was transformed from single intergranular fracture to intergranular and transgranular mixed fracture.It is found that the addition of Sc2O3 particles can obviously refine the grains and improve the sintering property of the materials.What's more,comparing the test results of the samples obtained by these two techniques,it demonstrates that MA followed by SPS is more suitable as the preparation technique for W-based materials.?2?The W–Zr/Sc2O3 composites with different contents of Zr?1 vol.%,3vol.%,5vol.%?were prepared by MA in vacuum followed by SPS.By comparison,W–1vol.%Zr/2vol.%Sc2O3 composite had the best comprehensive performance with the relative density of 98.93%,the microhardness of 583 Hv,and the grain size of 12?m.Compared with the brittle fracture of pure W,the W–Zr/Sc2O3 composites all had transgranular fracture in fracture position.However,an excessive amount of Zr led to the aggregation at the GBs,which was unfavorable to the combination of the GBs,decreasing the comprehensive performance of the materials.Results reveal that based on the addition of Sc2O3 particles which can refine the grains and improve the sintering property,the addition of appropriate amount of Zr alloying element will reduce the content of C,O and other impurities in the alloy,purify the GBs,eliminate the brittle thin layers and improve the bonding strength between the GBs,thus improve the mechanical property of materials.?3?The W–ZrC/Sc2O3 composites with different contents of ZrC?0,1 vol.%,3vol.%,5vol.%?were prepared by MA followed by SPS.Based on the addition of Sc2O3 particles which can refine the grains and improve the sintering property,co-doped by ZrC was added in the W-based composites.With the increase of ZrC,the relative density decreased and the microhardness gradually increased.For the W–3vol.5ZrC/2vol.%Sc2O3composite,the effects of different helium ion energies?50 eV and 80 eV?on the helium irradiation behavior were investigated at the same ion flux(1.0í1022 ions/?m2·s?)and irradiation time?2 h?.The action of the He?ions was found to induce a dramatic change in the surface morphology.Nano-filamentous structure?fuzz?and protruding structure occurred on the surface of the materials accompanied by radiation hardening after helium irradiation.There were large numbers of helium bubbles inside the fuzz structure,and the size of bubbles was between 510 nm.Such helium bubbles could exert a certain stress on the surrounding crystal lattice,resulting in the distortion in the original lattice arrangement.?4?D irradiation experiments were conducted on the composite materials of W–Sc2O3/?Zr,ZrC?system,and the effects of Sc2O3,Zr,and ZrC on the D retention behavior of W-based composites were investigated.The composite doped W–1vol.%Zr/2vol.%Sc2O3 composite had good deuterium retention resistance.After irradiation up to 1í1020 D2?/m2,the retained D amount of W–1vol.%Zr/2vol.%Sc2O3sample was 2.22í1015/m2,much lower than the other samples.The synergistic doped W–1vol.%ZrC/2vol.%Sc2O3 composite also had good deuterium retention resistance.The retained D amount of it was 1.80í1015/m2 after irradiation up to the same dose,which was better than those of W–1vol.%Zr/2vol.%Sc2O3 composite and SPS/W composite.With the increase of irradiation dose,the density and size of the defects introduced by irradiation damage increased and further absorbed D,leading to the increase of D retention in the materials.Pre-irradiation with 5 keV-He?ions to a fluence of 1í1021 He?/m2 would introduce new radiation defects into the material,providing traps for subsequent D2?ions irradiation,resulting in the appearance of new desorption peaks and an increase in D retention.However,the retained D amount of W–1vol.%ZrC/2vol.%Sc2O3 composite irradiated under 523 K was significantly lower than that at RT.The reason is that the type of traps has changed in this process.?5?On the basis of suitable amount of Sc2O3 which can refine the grains and improvethe sintering property,a moderate amount of Zr alloy element can reduce the contents of C,O,and other impurities in the alloy,purify the GBs,eliminate the brittle thin layers and improve the bonding strength between the GBs,further improve the thermodynamic properties of materials,while the addition of ZrC is not conducive to improve the thermal shock resistance of W-based composites.Results reveal that W–1vol.%Zr/2vol.%Sc2O3composite has the best thermal shock resistance.What's more,the contrast results of W–1vol.%ZrC/2vol.%Sc2O3 composite after thermal shock by electron beam were basically consistent with those by laser beam.During the thermal shock process,materials will inevitably produce cracks,corrosion,protruding structure,recrystallization,grain growth and other phenomena.Among these,the crack is the most typical.The occurrence of large cracks is related to the brittleness of W,whereas the small cracks are caused by plastic deformation at high temperature under the impact process.There were mainly three kinds of propagation modes after the formation of microcracks:1)the cracks went through the second phase directly;2)the cracks extended along the interface of the second phase and the matrix;3)and the cracks extended through the protruding structure directly. |
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