As the core component of the diffusion cathode, the performance of porous tungsten matrix material will directly affect the output performance and life of microwave source. Therefore, the preparation of porous tungsten matrix is the key process of making a cathode material. In this paper, the industrial tungsten powder was used as raw material, whose particle size was modulated by fluidic classification firstly. Then via cold isostatic pressing and hydrogen sintering in high temperature, the porous tungsten sintered body was obtained. Finally, by the process of copper infiltration, machining and copper removal, the porous tungsten matrix was achieved. The result showed that compared with raw material tungsten powder, the classified tungsten powder’s particle size distribution was narrowed and its tap density obviously increased, indicating that it had better particle stacking performance. Setting the temperature between 1900°C and 2050°C the high temperature hydrogen sintering experiment was conducted, and it was found that the volume shrinkage ratio of tungsten sintered body increased with the sintering temperature, and correspondingly, its total porosity decreased from 24.4% at 1900°C to 20.8% at 2050°C. It was characterized by MIP (mercury intrusion porosimetry) that at high temperature between 1950~2050°C, the porous tungsten matrix with an open porosity of 21±1%, 1.30~1.60μm average pore size, a close cell ratio less than 1% and the skeleton strength greater than 150MPa was obtained. Thus this porous tungsten matrix is an ideal material to be applied to highly reliable diffusion bariated tungsten cathode manufacturing.
Weld samples imitating the inservice girth welds in station (L245 straight pipe jointed to WPHY-70 tee joint and L415MB straight pipe jointed to WPHY-80 tee joint) were prepared. Tensile, bending, impact toughness and hardness of the joints were investigated. Results show that under tensile or bending load, failure occurred from the side with lower grade and smaller wall thickness. Relatived to the lower grade side, the weld seam is strong match. Significant change of impact toughness can be found in weld seam center and the heat affected zones (HAZ). The impact energy of seam center is the lowest in the weld joint. The impact energy show a trend of increase from seam center to base metal. In HAZ zone, impact toughness of the fusion line is the lowest. Impact toughness of higher grade side is higher than that of the lower grade side. Hardness of positions in HAZ zones are different distinctly. From coarse grained region to fine grained region, the hardness decrease. For the in-station girth welds jointed with different materials, lower grade and samller wall thickness side should be intensive monitored.
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