| Tungsten copper alloy is widely used in contact materials, electrode materials, aerospace ablation materials because of its good conductivity, thermal conductivity, arc erosion resistance and resistance to welding. It is well known that the coarse grain materials have good high temperature performance, but the fine grain tungsten copper alloy has the dispersed are, the arc ablation resistance. In this paper, CuW70 alloy with different particle sizes (grain sizes) were prepared by tungsten powder with different sizes and infiltration process. The effects of particle size on the microstructure and properties of tungsten-copper alloy were investigated by SEM,high-temperature creep experiments and simulated high-pressure arc ablation experiments. At the same time, the Electron Capability of Field Emission of CuW70 alloy with different particle sizes was calculated and analyzed by First Principle. The Electrification Mechanism of Arc Ablation of fine grain tungsten-copper alloy was studied. Research results indicates:(1) At room temperature, the hardness and compressive strength of tungsten-copper alloy decrease with the increase of particle size, and the conductivity increases with the increase of particle size. When the particle size changed from 0.52 ?m to 20.69 ?m, the relative density,hardness, compressive strength and electrical conductivity changedfrom 99.2%, 202 HB,1232.17 MPa, 42.8% IACS to 97.5%, 179 HB, 1116.31 MPa, 44.6 %IACS, respectively. At high temperature, the coarse grain tungsten-copper alloy showed good creep resistance. With the decrease of the particle size, the creep life of the alloy became shortened .When the particle size changed from 0.52?m to 20.69 ?m, the life of alloy changed from 26.3 h to 87.2 h.(2) At room temperature, the fracture morphology of the specimen is typical cleavage fracture morphology, fracture is mainly W-Cu interface fracture and W-W interface fracture. At high temperature, the internal heating temperature is too high, weakening the interfacial bonding strength formed by the tungsten phase and the bonded phase copper. The shear stress required for the copper phase fracture is lower than that of the tungsten. Therefore, the crack is easily generated at the interface of the two phases and the copper phase. The final fracture is made mainly by W-Cu interface fracture and copper ductility fracture.(3) Under the same breakdown voltage, the first breakdown of the ablation area of fine grain was larger than that of coarse grain, breakdown pit more and shallower. After 100 times electric breakdown, the surface of the fine-grained tungsten copper alloy has copper splash deposition, bringing about a large number of holes and the exposed tungsten skeleton, the more coarse the particles the more obvious the phenomenon. Fine-grained copper dispersed, rapid heat dissipation, large ablation area and ablation was relatively moderate. Coarse grain alloy copper phase was relatively concentrated, ablation focused in this region led that a large number of copper loss and ablation became serious finally.(4) Resistant to arc ablation of fine grain more than that of coarse grain, and the mechanism first was that copper phase of fine tungsten-copper alloy distributed smally and evenly, arc will no longer gather on the rich copper area, but evenly distributed in the cathode material surface. Second, the W skeleton in fine grain tungsten-copper alloy dense, tiny copper droplets can be embedded in the tungsten skeleton which made the alloy surface still smooth after many times breakdown, field emission electrons probability caused by slightly raised reduced, and it benefited electrical breakdown function of the material. Third, the reduction of work function of the fine grain boundary, reduced the cathode temperature and material evaporation for the reduction of the arc ablation.(5) With the increase of the electric field, the density of states of the tungsten-copper alloy Fermi level increased, the external electric field changed from 0.087 Ha to 0.12 Ha, the density of states increased from 199.62 Ha to 244.01 Ha. Fine grain tungsten-copper alloy with high voltage strength,the external electric field strength was lager. The density of states refers that the number of electrons with the scope of unit energy, so fine grain field emission electrons was stronger than that of coarse grain. Causes why fine grain tungsten-copper alloy has resistance to arc erosion, first, fine particles of tungsten-copper alloy, the uniform distribution of tungsten and copper phase made the barrier width narrowed, the electrons easy to pierce the solid surface,and the field emission electrons was strong, second, The internal electric field was formed at the grain boundary of tungsten and copper. The electrons accumulate at the grain boundary where the electric breakdown occurred easily. The fine grain boundary was more than coarse, the electron emission points were dispersed on the surface of the material, which made sample ablation lighter. |
PDF Full Text Request