Cryogenic processing of porous tungsten framework
The porous tungsten framework sintered at high temperature is easy to be brittle and cannot be machined. As mentioned above, tungsten copper (plastic) material is obtained by infiltrating copper or plastic to improve its processing performance, and then turning is carried out. The dimensional tolerance of cathode emission surface machining is + 10μm. The surface roughness is not higher than 0.8μm; however, the infiltrated copper or plastic can effectively support the pore structure and be used as processing lubricant, and the infiltration and removal process is time-consuming, laborious and may cause residual pollution. First found that porous tungsten based on diffusion cathode application can be directly cryogenic processed at liquid nitrogen temperature (- 180°C), which can not only obtain clean and high-quality machining surface by avoiding the pollution of conventional cooling medium and timely removing processing debris, but also make the porous tungsten workpiece (ductile brittle transition temperature from room temperature to 300°C) in the processing mechanism dominated by brittle fracture due to deep cooling. Subsequent optimization studies by show that the deep cold machining of porous tungsten can be realized by using modified fine-grained polycrystalline diamond tools in and the porosity of surface machining is controllable and close to the inner porosity of matrix, which is expected to replace plastic infiltration.
