奈米與微米碳化鎢塗層之抗鋅液腐蝕研究

Corrosion of Nano-structured and Conventional Tungsten Carbide Coatings in Molten Zinc

鈷基碳化鎢塗層目前被廣泛用於熱浸鍍鋅線之鋅槽輥的表面處理，可延長輥面使用壽命，並提昇熱浸鍍鋅鋼板之表面品質。而近年來開發之奈米碳化鎢塗層，較傳統微米碳化鎢塗層有較佳的材料特性。本研究利用高速火焰熔射技術製作奈米與微米碳化鎢塗層試片，進行材料特性評估與鋅液腐蝕測試。實驗結果發現，奈米碳化鎢塗層有較高硬度、較低孔隙率及較佳韌性，然而，其耐鋅液腐蝕卻不如微米碳化鎢塗層。鋅液腐蝕機構主要為熔融鋅與塗層裡的鈷之交互作用，一旦鈷被擴散至鋅液中，顆粒較小的奈米碳化鎢比顆粒較大的微米碳化鎢更容易從塗層中脫落。

WC-Co coatings are widely used for sink rolls in a continuous galvanizing line. They can extend the service life of the rolls from being attacked and improve the quality of galvanized steel sheets. Recent developed nano-structured WC-Co coatings exhibit better material properties than conventional micro-structured ones. In this study, a high velocity oxy-fuel (HVOF) spray gun was used to prepare nano-structured and conventional WC-Co coatings. Material properties and their corrosion resistances in molten zinc were evaluated. The results showed that the nano-structured WC-Co coating had a higher hardness, a lower porosity and a better toughness. However, the conventional WC-Co coating exhibited better ability against molten zinc corrosion. The main mechanism of molten zinc corrosion is the inter-diffusion of molten zinc and Co. When Co diffuses into the molten zinc, nano-sized WC particles would become easier to detach from the coating than micro-sized ones.