Effect of Tungsten Powder Granularity on Tungsten Copper Micro-structure

Similarly takes tungsten copper W-30Cu electrode as an example, compared with tungsten copper electrode by tungsten powder with different granularities at the same temperature SEM pictures, we can find that tungsten copper W-30Cu electrode with similar composites, the smaller the particle size of the tungsten powder, tungsten powder dispersed more evenly, but the greater the possibility of the obturator and defects, W grain size is uneven, resulting in an overall lower uniformity; on the contrary, the larger the tungsten powder particle granularity, the greater the corresponding grain size, dispersibility of the tungsten particles is reduced, the connection between the tungsten particles is weakened so that the amount of bores decreased. The following are the different particle size of tungsten powder prepared W-30Cu tungsten copper alloy electrodes SEM photograph, from left to right are the tungsten powder particle size (a) and (b) -2.9μm, (c) and (d) -4.2 -4.8μm, (e) and (f) -11-13μm:

Theoretically, the porosity of tungsten copper W-30Cu with smaller granularity is smaller than the coarser one at the same sintering temperature. This is due to in the process of sintering (surface diffusion plays an leading role at 1350℃ sintering temperature) with the decreasing granularity of powder, the free energy will increase, which further promotes the sintering processing. While interconnected particles occurs first in the surface of the particles.

The finer the grain size of tungsten powder, which means larger specific surface area, active surface atoms, the more the (surface energy increases), so that the surface diffusion easier to carry out. Reduced powder size is also thought to increase the diffusion of the interface between the particles, and to shorten the diffusion path, thus increasing the number of atoms per unit time-proliferation. In addition, the granularity too coarse to cause uneven tungsten skeleton bores and lead to the appearance of copper enrichment after the infiltration; and the particle size is too prone to particle agglomeration Details such tungsten skeleton prone channel closed or blocked, leading to infiltration of liquid copper is difficult to completely infiltrated, leaving part of the pores in the products, so that the uneven distribution of tissue composition of the product. Therefore, the granularity and the combination of the granularity has an remarkable influence on infiltration process.

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