Microstructure and growth mechanism of tungsten carbide coatings by atmospheric CVD

A tungsten carbide coating was prepared by atmospheric chemical vapor deposition (CVD) with tungsten hexafluoride (WF₆), hydrogen, and dimethyl ether (DME) as the reaction gases, under a dimethyl ether partial pressure (P_DME) of 3.2–21.0 kPa and a temperature of 550–600 °C. The phase compositions of the coatings are W₂C + W and W₃C + W, and it is found that when P_DME is low, the coating has a lamellar structure, but at a high P_DME, the lamellar structure and fibrous tissue are simultaneously present in the scanning electron microscope (SEM) image. In the latter case, no delamination was found, which was visible at a low P_DME. In addition, as the P_DME increases, the deposition rate of the coating decreases, and ultimately, the coating cannot continue to grow. The growth model of the tungsten carbide coating based on the kinetics of the chemical vapor deposition of tungsten by the hydrogen reduction of tungsten hexafluoride was proposed, and the influences of P_DME and temperature on the coatings were discussed and the orientation relationship between W and W₂C in high resolution transmission electron microscopy (HRTEM) was analyzed.