Fabrication And High Heat Flux Performance Of W/Cu Functionally Graded Coatings By Low Pressure Plasma Spray

The research status and development trends of plasma facing materials which applied innuclear fusion reactor were first reviewed in this thesis. It is really difficult job for connectingbetween plasma facing materials (tungsten) and heat sink material (copper) due to the greatmismatch of their physical properties. The distributions of thermal stresses and surfacetemperature for the three-dimensional model of W/Cu functionally graded coatings weresimulated by finite element ANSYS Workbench code under the steady-state heat load. Basingon the simulation results, a series of W/Cu functionally graded material (FGM) were preparedon the CuCrZr substrate by low pressure plasma spraying (LPPS). The effects of surfaceroughness, as well as different types and thicknesses of graded layers on the relaxation ofthermal stress and bond strength between copper and tungsten were studied. In addition, themicrostructure and composition analysis of W/Cu FGM were characterized by opticalmetallographic microscope, scanning electron microscope and energy dispersive spectroscopy.Finally, the high heat flux performance of W/Cu FGM under the steady-state thermal fatigueand transient thermal shock were evaluated by the60kW Electron-beam Material testingplatform.The results showed that with the number of graded layers increasing, the von misesstress was reduced, and reached the minimum value when number of gradient layer was six,then it changed within a wavy motion after the graded layers over six. Besides, with theincrease of compositional exponent (p-value), the von mises stress firstly decreased sharply,and then no remarkable change was observed when p-value increased to ten. Further more,the von mises stress decreased significantly along with the increment of graded layers’thickness, but the surface temperature rised gradually. Therefore, taking the three factors intoaccount, the six-layer model with the compositional exponent of1.8seems to display goodhigh heat flux performance.Different types and thicknesses of transitional graded layers of the W/Cu and thick Wcoating were elaborated on the CuCrZr substrate by LPPS. The thicknesses of W coatingswere ranged from1.35to1.61mm, the microstructure of W coatings were dense, however,porous areas were observed in the W coating near to the graded layers; Meanwhile, the twotypes of graded layers were W/Cu and Mo/Cu, the number of graded layers was six, and thethicknesses of graded layers were ranged from0.38~0.83mm. The entire gradient layersexhibited a continuous and good lap without any interface between each layer. What’s more,the oxygen content for W coatings were as low as0.1±0.02wt.%, the thermal conductivity was ranged form32to39W/(m·K), and the porosity was in a range of9±1vt.%, the key poresize distribution for all the W coatings was ranged from0.2to4.0μm, especially focus onabout1μm.W06-h model could withstand the impact of power density of9MW/m~2for1000thermalfatigue cycles under steady-state heat load, and no overheating zones and hot spots wereoccurring during the whole test campaign, and the maximum surface temperature deviationwas at around10%, no cracks were observed at both the surface and the interface, indicating agood bonding of W and CuCrZr alloy. Therefore, the results were agreed well with theevaluation criteria of the high heat flux experiment. Moreover, W06-h model withstood thetransient thermal shock of energy density for20MJ/m~2without longitudinal crack propagation,but micro-cracks on the surface of W coating under vertical displacement events mode,however, for the plasma burst mode, W06-h model could withstand the transient thermalshock of energy density for4MJ/m~2, just micro-cracks on the surface were found.