Effect of deposition position on microstructure of HfC coating

In order to research the effect of deposition position on HfC coating, the coating was prepared on the surface of C/C composites by LPCVD (low pressure chemical vapor deposition), using HfCl₄-C₃H₆-H₂ reaction system. The phase composition, grown orientation, surface morphology and the deposition rate were analyzed by X-ray diffractometer and scanning electron microscope. Results show that a flat and compact HfC coating with no carbon phase was obtained at 20~25 cm above the gas inlet. As the deposition position became far away from gas inlet, the coating deposition rate tends to decrease due to the reduction of reactants concentration. Moreover, the grain size is also reduced obviously, and the coating behaves preferred orientation growth following (200) plane.