Preparation,microstructure And Performance Of Diamond/Tungsten Based Composites For Fusion Reactors

Tungsten and tungsten-based composites have high temperature resistance,high strength and low sputtering rate,and they have attracted widespread attention in plasma-facing component materials,such as tungsten using as the first wall materials and W-Cu using as the connecting materials.In the above applications,high requirements are put forward on the thermal properties of the materials.The excellent thermal properties of diamond have been successfully applied in diamond copper-based and diamond silver-based composites.However,diamond has insufficient stability at high temperatures and there are relatively few studies on the feasibility of introducing diamond into tungsten and tungsten-based materials.To improve the thermal performance of plasma-facing components in fusion reactors,this thesis attempts to add diamond into related W-based materials,and conducts research on the preparation,structure and performance of the diamond/W and diamond/W-Cu composites.The main contents and conclusions of the full text are as follows.(1)Because of the interfaces between diamond and metal matrix have obvious influence on the properties of diamond/metal matrix composites,this research first carried out microwave heating salt bath method to plate tungsten and titanium on the surfaces of diamond particles.The results show that the thickness of the W coating layer is about 200 nm and the surface undulation of the coating reaches 670 nm after microwave heating salt bath plating tungsten at 1200?for 20 minutes.An interlayer containing W₂C and WC formed between dimond particle and tungsten coating,which makes the tungsen coating and diamond particle bond closely.A complete and dense titanium coating was formed on the surface of diamond particle after microwave heating salt bath plating at 850?for 20 min,while only a relatively complete titanium coating was obtained after conventional salt bath plating at 900?for 120 min.(2)Traditional electroless plating copper requires the use of precious metal palladium as activator.This paper developed a novel tungsten coating sensitization and activation electroless plating(TCSAEP)method to achieve electroless plating copper on the surface of diamond particle.The results show that the surface of tungsten-coated diamond can be directly plated with copper.by TCSAEP method.There an interlayer containing W₂C,WC and W are existed between the dimond particles and the copper coatings after tungsten-coated diamond electroless plating copper by TCSAEP method.Copper-coated diamond/copper composites and uncoated diamond/copper composites were prepared by microwave sintering at 920?for 30 min.The relative density and thermal conductivity of copper-coated diamond/Cu composites are 98.8%and 522W/(m·K),which are higher than the corresponding performance of uncoated diamond/Cu composites(92.3%,265 W/(m·K)).(3)Tungsten-coated diamond particles obtained by the MHSBP method and W-Cu composite powders obtained by electroless plating are used as raw materials,and W-30Cu composites with different contents of tungsten-coated diamond are prepared by microwave sintering.The results show that when the content of tungsten-plated diamond is 4 wt.%(14.5 vol.%),the thermal conductivity of diamond/W-30Cu composites reaches the highest value of 239.56 W/(m·K),which is 17%higher than that of W-30Cu without adding diamond particles.The theoretical calculation shows that the total interface thermal resistance between tungsten-coated diamond and W-Cu in the tungsten-coated diamond/W-30Cu composites is 2.08×10^-8 m²·K/W,which is much lower than the interface thermal resistance(7491×10^-8 m²·K/W)between uncoated diamond and W-Cu.(4)Based on the service environment of plasma-facing components in fusion reactors,5 wt.%tungsten-coated diamond was added to the W-40Cu layer of W-Cu functionally graded material(FGM)(W-10Cu/W-20Cu/W-30Cu/W-40Cu).The tungsten-coated diamond/W-Cu FGM was prepared by microwave sintering.The results show that the relative density of tungsten-coated diamond/W-Cu FGM is 94.66%after microwave sintering at 1200?for 30 min.When the W-40Cu-5Diamond surface is used as the compression surface,the bending strength of tungsten-coated diamond/W-Cu FGM is550.5 MPa,which is lower than the bending strength of W-Cu FGM(730.5 MPa).The thermal conductivity of the tungsten-coated diamond/W-Cu FGM reaches 220.38W/(m·K),which is higher than the thermal conductivity of W-Cu FGM(209.63W/(m·K)).After laser thermal shock with a power density of 0.64 GW/m²,ablation pits with a radius of about 300?m appeared on the W-40Cu-5diamond surface of tungsten-coated diamond/W-Cu FGM,but the overall structure of tungsten-coated diamond/W-Cu FGM remained stable.(5)Diamond/tungsten composites were fabricated by spark plasma sintering(SPS)in view of the poor thermal stability of diamond.The stability of diamonds in diamond/tungsten composites and the influence of diamonds on the radiation resistance of diamond/tungsten composites were studied.The results show that diamond can stably exist in the diamond/tungsten composites after spark plasma rapid sintering at 1600?for 3 min.When the diamond content is 5 wt.%(22.4 vol.%),the density,thermal diffusivity and thermal conductivity of the uncoated diamond/tungsten composites are14.69 g/cm³,80.86 m²/s and 180.55 W/(m·K),respectively.In contrast,the interface of tungsten-coated diamond/tungsten composites is more tightly bonded,and its corresponding performances are increased to 15.13 g/cm³,85.16 m²/s and 192.91W/(m·K).After being helium ions irradiated with a total flux of 4×10²² ions/m²,the diamond in the tungsten-coated diamond/tungsten composites was destroyed completely.The result proves the rationality of introducing diamond particles into pure copper layer and high copper layer of W-C FGM.