Effect of Total Flow Rate on Microstructure and Growth Mechanism of ZrC Coating Prepared by LPCVD

Zirconium carbide (ZrC) coatings were deposited on graphite substrate at 1200 degrees C by low pressure chemical vapor deposition (LPCVD) using the Zr-Br-2-C3H6-H-2-Ar system. The effects of total flow rate on the microstructure and growth mechanism of ZrC coatings were investigated. The results show that as the total flow increases, the deposition rate increases firstly and then decreases slowly, and the deposition rate reaches the maximum of 3.37x10(-3) g.cm(-2).h(-1) at the total flow rate of 800 mL/min. Meanwhile, the preferential orientation of ZrC coatings changes evidently, and the (200) plane is the preferential orientation of ZrC coatings at the total flow rate of 600 similar to 800 mL/min. XPS results show that the C/Zr ratio of ZrC coatings increases from 0.85 to 1.49. At the total flow rate is 200 mL/min, the ZrC coatings are dense and composed of equiaxed gains. As the total flow rate increases from 400 to 800 mL/min, the ZrC coatings are well-faceted pyramidal-shaped crystals. When the total flow rate is 1000 mL/min, the ZrC coatings own loose complex island-like gains. The variation of ZrC coatings is mainly attributed to the boundary layer with increasing the total flow rate.