以EBSD觀察鉻鉬鋼熱浸鋁化層於高溫之相變化

Phase Transformation in the Aluminide Cr-Mo Steel at High Temperature Observed by using EBSD

本研究使用5Cr-0.5Mo鋼經熱浸鍍鋁後，於750℃空氣進行擴散，利用電子背向繞射（Electron Backscatter Diffraction, EBSD）技術，分析Fe-Al鋁化層在高溫所發生的相變化。實驗結果顯示，熱浸後的鋁化層，由外層的FeAl3相及內層的Fe2Al5相所組成。隨高溫暴露時間之延長，Fe2Al5相持續成長，FeAl3相的厚度則無明顯改變。但當最外側的熱浸純鋁塗層消耗完後，FeAl3也隨之消失。於750℃保持60分鐘後可以發現到FeAl2相於Fe2Al5相的內外兩側生成，並有FeAl相出現於FeAl2與基材之交界處。長時間擴散後，FeAl相成長，且FeAl2相取代了大部分的Fe2Al5相。此外，由晶粒取向圖（Crystal Orientation Map, COM）顯示，Fe2Al5相皆沿著晶體結構中C軸[001]的方向成長。

5Cr-0.5Mo steel was coated by hot-dipping into a molten bath containing pure Al. The phase transformation 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 in the as-coated specimen consisted of an outer FeAl3 layer and an inner Fe2Al5 layer. The Fe2Al5 phase kept growing with increasing exposure at 750 ℃, but the FeAl3 phase didn’t change significantly. The FeAl3 phase disappeared once the aluminum layer was consumed. After 60min of exposure at 750 ℃, FeAl2 phase formed at the inner and outer sides of the Fe2Al5 phase while FeAl phase formed at the interface between FeAl2 and the steel substrate. With prolonged exposure, the thickness of FeAl increased and the volume of FeAl2 expanded at the expense of Fe2Al5. Based on Crystal Orientation Map (COM), Fe2Al5 grew preferentially along the C-axis, [001] direction, of the crystal structure.