Cause of Tungsten Tube Surface Longitudinal Cracks

The main cause of CVD tungsten tube longitudinal cracks lies that: the deposition way of the inner wall of tungsten tube and the deposition process is not well controlled. The fundamental reason is that the tensile stress due to tungsten tube’s wall contraction (its cooling speed is too fast, and the amount of reaction gas is too much in unit time). Because the stress is concentrated at the growing crystal grain boundaries, so these positions are easy to crack. Growth of columnar crystals of tungsten tube is growing along the radial direction, leading to rapid expansion of the crack into the grain boundaries.

The depositing of tungsten tube inner wall is by heating the outer wall of the deposited matrix to the deposition temperature.

In the cooling process of the deposition, the inner wall of deposition tungsten tube will cooling rapidly due to continuous passing-through of hydrogen, while the outer wall of the cooling rate will be relatively slow.

 

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