Study On Preparation,Modification And High Heat Flux Testing Of Atmospheric Plasma Sprayed Tungsten Coating

Atmospheric plasma spraying(APS)is a high-efficiency,economical and convenient coating technology,providing a possible solution to the problem of the preparation of tungsten for plasma facing material and the connection of tungsten and heat-sink copper.However,the traditional APS-W coating has some inherent defects,such as high oxygen content,high porosity,and low bonding strength of tungsten and copper.To this end,the thesis has investigated preparation,performance optimization of tungsten coatings by APS and carried out evaluation of the thermal load capacity of the plasma sprayed tungsten materials and the tungsten-copper water-cooled components.In the preparation of tungsten coatings,a series of measures were adopted to optimize the APS process,including high-speed plasma spraying method,submicron tungsten powder spraying method and active water-cooled spraying method,which improved the performance of sprayed tungsten coatings.The properties of tungsten coatings prepared by these improved methods were measured,showing better performance compared to the tungsten coatings prepared by the traditional APS.Annealing and surface remelting measures were innovatively proposed to improve performance of the tungsten coatings,the feasibility of improving the performance of APS tungsten coatings through post-treatment was explored.The effect of vacuum and hydrogen atmosphere annealing at different temperatures,and the changes in the microstructure of plasma sprayed tungsten coatings under the impact of the high-energy electron beam were studied.The results show that the annealing treatment could decrease the oxygen content in the coatings by reducing the tungsten oxide into tungsten.After annealing treatment at a certain temperature,recrystallization of the tungsten coatings was observed.The porosity of coating decreased and the coatings became more compact,which significantly improved the microhardness and the thermal conductivity of the coatings.After remelting,the microstructure of the sprayed tungsten coating changed from layered mechanical bonding to metallurgical bonding,and the microhardness and purity of the coating were improved.Based on the requirement of high heat flux testing for plasma facing materials and components,two electron beam platforms for simulating high heat flux testing have been established,including a transient platform with an energy density of 100 J/cm2 and a steady-state platform with a power of 100 kW and a scanning frequency of 10 kHz,together with calibrated necessary instruments and equipment,allowing both of platforms to carry out high heat flux testing and to evaluate plasma facing materials and components.In this thesis,the transient testing on the APS tungsten coatings were first performed in comparison to the chemical vapor deposition(CVD)tungsten coatings.Under the impact of electron beam with high power density,the surface of the APS tungsten coating has melting,recrystallization,evaporation and flaking phenomena,there is a slight loss of coating quality without penetrating cracks.No melting phenomenon was found on the surface of the CVD tungsten coatings,but reticular cracks appeared,and the cracks tended to widen and become denser with the increase of the power density of pulsed heat flux.Then the testing and evaluation of performance of the sprayed tungsten-copper water-cooled component was carried out on the steady-state platform.The temperature changes of the surface and interface of the component under different cooling water flow rates and different power density heat flux were studied.The results show that the APS tungsten-copper water-cooled component successfully withstood 500 cycles thermal fatigue shocks at heat flux of 8.5 MW/m2,and the surface temperature was close to 900?.Through these experiments,the performance of APS tungsten materials and components was evaluated,the reliability and the first-hand data of the two high heat flux testing platforms have been verified and obtained,and rich experience and lessons have been accumulated for further application and upgrading of the platforms.