以EBSD觀察低碳鋼熱浸鋁化層的成長行為

Observation of Growth Behavior in the Aluminide Mild Steel Using EBSD

本研究使用低碳鋼經熱浸鍍鋁後，於750℃空氣氣氛下進行擴散，並藉由電子背向繞射（Electron Backscatter Diffraction, EBSD）技術，分析鋁化層的成長行為。實驗結果顯示，熱浸後的鋁化層，由外至內，為表層的純鋁鍍層、少量的FeAl3相與主要相Fe2Al5所組成。此外，Fe2Al5具有舌片狀形貌，並造成交界的基材呈現相對應的鋸齒狀形貌。經由高溫擴散，部分鋸齒狀的尖端將與基材分離，並伴隨孔洞的產生。當鋁鍍層消耗完後，FeAl3也隨之消失，此時鋁化層由單一Fe2Al5相組成。於750℃保持60分鐘後，可以在Fe2Al5相與基材界面處發現FeAl2與FeAl相的生成。隨擴散時間之延長，FeAl2與FeAl相將持續成長，並伴隨空孔的增大及鋸齒狀形貌的消失。長時間擴散後，鋁化層將由FeAl2與FeAl相所組成。

Mild steel was coated by hot-dipping into a molten aluminum bath. The growth behavior in the aluminide layer during diffusion at 750 ℃ in static air was analyzed by Electron Backscatter Diffraction (EBSD). The results showed that the aluminide layer of the as-coated specimen consisted of an outer aluminum topcoat, minor FeAl3, and major Fe2Al5, respectively. Besides, Fe2Al5 possessed a tongue-like morphology, which caused the corresponding serration-like morphology of the steel substrate. A portion of the peaks of serration-like substrate were isolated and accompanied by the formation of voids with increasing exposure time at 750 ℃. The aluminide layer composed of single Fe2Al5 phase as the aluminum layer was consumed, leading to the disappearance of FeAl3. After 60 min of exposure, FeAl2 and FeAl phases formed at the interface between Fe2Al5 and the steel substrate. With increasing exposure time, the voids condensed and the serration-like morphology disappeared, while FeAl2 and FeAl phases kept growing. After prolonged exposure, the aluminide layer composed of FeAl2 and FeAl.