Tungsten Copper Heat Sink Plasma Spraying (2/2)

The researchers use two kinds of spray gun (internal and external powder feed) to observe the structure and properties of tungsten copper heat sink. It can be found that in the internal powder feeding conditions, W content of tungsten copper composite material is higher than the content of external powder feed. This is due to internal feed powder is powder being ejected before the gun are all located in the plasma flame, part of the W particle is melted, melted and un-melted W particles, and the molten copper solution together is sprayed into the substrate, so that easy obtain raw material powder composition approximating tungsten copper composite material; while in the process of external powder feed, he trajectory of the powder particles are not entirely consistent with the plasma flame, which can only make a fraction of smaller particle size of the W particles melt, and a lot without melting of W particles are difficult to be deposited, so the W collected rate decrease.

Besides, at internal powder feeding conditions, only a small amount of cuprous oxide can be detected, which indicates the impact of power in copper oxidation is not obvious. This is due to the internal powder feeding only a very small amount of oxygen is brought into a powder particle flow, thereby largely avoiding the oxidation of copper; by contrast, in the same power, a large number of external powders feed oxygen into the powder particles flow and exacerbates the copper oxide. With the power increase, the plasma flame temperature also increases, the oxidation of copper increased significantly. Overall, plasma spraying uses plasma arc, which compared with free arc has fine arc, high current density, and high degree of gas ionization. So it has many advantages, such as high temperature, high energy concentration, excellent arc stability, which is the ideal material for tungsten copper heat sink.