Copper infiltration of porous tungsten framework
The porous tungsten billets sintered at high temperature are brittle and can not be machined. The turning performance can be improved after copper infiltration. In general, the copper melt infiltration method is used, that is, the tungsten sintered billet contacts with the liquid copper, and the connected pores in the tungsten billet are effectively filled by the liquid copper through capillary force. After cooling, the tungsten copper material can be obtained, which can increase the density, strength, hardness, plasticity or impact toughness of porous tungsten. According to the copper infiltration feeding mode, it can be divided into basket infiltration, pushing boat infiltration, laminated infiltration, wrapping infiltration, etc.; according to the copper infiltration pressure, it can be divided into pressureless infiltration, extrusion infiltration, air pressure infiltration, etc.; according to the copper infiltration atmosphere, it can be divided into hydrogen infiltration, vacuum infiltration, argon infiltration, etc.; according to the type of copper infiltrating skeleton, it can be divided into high temperature sintering pure tungsten skeleton and low-temperature sintering part of copper tungsten skeleton. Compared with the traditional electrode, throat liner and other applications, the application of diffusion cathode puts forward higher requirements for copper infiltration of porous tungsten framework: copper infiltration should be more sufficient and uniform at the micro level. Otherwise, in the process of machining, especially the finishing machining based on emission quality, the defects such as local damage may appear at the place where the emission surface is not sufficiently uniform, which is easy to form a strong electric field and cause breakdown, which will affect the reliability and uniformity of emission. At present, porous tungsten matrix copper infiltration is still a necessary and key process in the application of diffusion cathode. The comprehensive properties of the prepared tungsten copper materials are good, but the production process is complex and the production cycle is long. Among them, air pressure copper infiltration and pressureless copper infiltration combined with hot isostatic pressing are dense chemical process is the first choice for high quality tungsten copper materials for diffusion cathodes.
