Fabrication of uniform ZrC coating by low pressure chemical vapor deposition: The in-situ bromination method

Abstract:

A bromination apparatus was designed and manufactured to accurately control the flow rate of ZrBr₄ vapor. Zirconium carbide (ZrC) coatings were deposited on graphite substrate at 1200°C by low pressure chemical vapor deposition from the Zr-Br₂-C₃H₆-H₂-Ar system. The effects of gas composition (input C/Zr ratio) on the morphology and growth mechanism of ZrC coatings were investigated. The coating deposition process was controlled by the surface reaction kinetics at the input C/Zr ratio of 1.5, leading to a loose structure. When the input C/Zr ratios were 0.5 and 1, coating growth was dominated by diffusion kinetics, resulting in (200) preferential orientation with a dense columnar structure. Meanwhile, ZrC coating without free carbon was produced at the input C/Zr ratio of 0.5.

Key words:ZrC coating; ultra-high temperature ceramic; microstructure; chemical vapor deposition; gas composition; growth mechanism.