Construction And Irradiation Resistance Of HfNbTaTiZr High Entropy Alloy Coating Systems On Tungsten For Plasma Facing Materials Application

The fusion energy produced by nuclear fusion reaction is an important potential way to solve the existing energy problems.However,the selection of fusion device materials,especially plasma facing materials（PFMs）,restricts the development of controllable nuclear fusion reaction,which has become a difficult problem to promote nuclear fusion reactor to engineering application or commercialization.W is considered to be the first candidate material directly facing the plasma for future nuclear fusion devices because of its high melting point,high density,high thermal conductivity,high resistance to particle sputtering and low tritium retention.However,as PFMs in direct contact with high-energy plasma,W will appear defects such as He bubble,H bubble,Fuzz structure,cavities and dislocation loops under the scouring of a large number of H ions,He ions and neutrons,resulting in irradiation swelling,irradiation hardening and irradiation embrittlement of W.Thus,the toughness of the material is reduced,the brittleness and the ductile brittle transition temperature of the material are increased,which affects the stable operation of PFMs in the nuclear fusion reactor.Therefore,improving the radiation resistance of W has become the key to its application as PFMs in nuclear fusion reactor.In this experiment,HfNbTaTiZr high entropy alloy coatings were prepared on the surface of W by double glow plasma surface alloying technology.Through the characterization of alloy coatings prepared by surface alloying,such as morphology observation,composition analysis,phase detection,bonding strength test and microhardness test,the best preparation process was optimized,and the anti He⁺irradiation performance of HfNbTaTiZr high entropy alloy coatings were evaluated.The main research contents and results are as follows:（1）The morphology,composition,phase,bonding strength and microhardness of high entropy alloy coatings prepared under different processes were analyzed and tested.Due to the bombardment of Ar plasma during the preparation process,the surface roughness of the coatings were increased compared with that of the substrate.The prepared coatings are composed of deposition layer and diffusion layer.When the alloying temperature was 950℃,the cathode source extreme pressure difference was 300 V,the electrode spacing was 18 mm,the working pressure was 35 Pa and the holding time was 3 h,the granular morphology of the alloy coating surface was the most compact,and the proportion of the alloy composition on the surface was the most similar to that of the target element.The coating prepared by this process had no obvious cracking between the deposition layer and diffusion layer,between the coating and the substrate,and the coating thickness is uniform.The surface hardness of the coating prepared under this process was the largest.The scratch test results also showed that the alloy coating prepared at this temperature had excellent bonding with the substrate.（2）Pure W samples and HfNbTaTiZr high entropy alloy coating samples prepared under all processes were irradiated with low energy and high flux He⁺with the energies of 30 e V,fluxes of 2.75×10²¹ ions/m²?s and doses of 7.425×10²⁴ ions/m².After irradiation,uniform Fuzz structure was generated on the surface of W.The surface of HfNbTaTiZr high entropy alloy coating samples may appeared the early stage of Fuzz structure-waves/terrace morphology,or only produced Fuzz damage in local area,that was,the damage was slight.The results showed that the coating prepared in this experiment could effectively resist the irradiation damage caused by He⁺on the W surface.The surface of the coating samples with local Fuzz damage after irradiation had obvious composition segregation,while the surface of the coating samples with waves or terrace morphology was evenly distributed without obvious agglomeration.After He⁺irradiation,the composition content of the alloying coating sample prepared under the metallization process with temperature of 950℃,the cathode source extreme pressure difference of 300 V,the electrode spacing of 18 mm,the working pressure of 35 Pa and the holding time of 3 h was almost the same as that before irradiation,and only terrace and waves shapes appear on the surface after irradiation.The results showed that the alloying coating sample prepared under this metallization process had the best resistance to He⁺irradiation.