The Hardness of Tungsten Tube Prepared by CVD (Chemical Vapor Deposition) (1)

Tungsten tube prepared by CVD (Chemical Vapor Deposition), which has the same diameter and other factors, and the deposition temperature is between  500 ℃ and 700℃, the hardness test results of deposited tungsten layer shows that the hardness of tungsten tube prepared at different temperature are higher than 500HW. If the diameter is different, the hardness of tungsten tube will decrease with the increasing of tungsten tube diameter; at different deposition temperature, the hardness of tungsten tube prepared will decrease resulting from the increase of distance between deposition matrix and tungsten tube.

The analysis of the change of the deposition layer hardness result shows that the change is related to the internal stress generated in the cooling process after the end of deposition and the crystal growth of the film layer. In the process of the growth of the film deposition in the inner surface of the base, the matrix is perpendicular to the columnar grain growth caused by the mutual pressing of the deposited layer, which having a larger residual stress. The smaller the radius of the tungsten tube, the residual stress caused by column crystal squeezing each other will be larger. In the range of 273-1273K, average linear expansion coefficient of tungsten, copper are 4.4×10^-6K^-1,17.0×10^-6K^-1. In the cooling process after depositing, tungsten tube volume shrinkage is much smaller than the copper matrix, which will result in greater residual stress on the surface of deposition tungsten tube.


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