利用EBSD鑑定鉻鉬鋼熱浸鋁矽塗層中Fe-Al-Si介金屬相之晶體結構

Crystallographic Identification of Fe-Al-Si Intermetallic Phases in Si-modified Aluminide Coatings on Cr-Mo Steels by EBSD

本研究採用5Cr-0.5Mo鋼熱浸於700℃之鋁-10 wt.%矽熔湯中10、60、120與180秒。藉由掃瞄式電子顯微鏡（Scanning Electron Microscope, SEM）、能量分散光譜儀（Energy Dispersive X-ray spectroscopy, EDS）、X-ray繞射儀（X-ray diffraction, XRD）與電子背向繞射（Electron Backscatter Diffraction, EBSD）技術，鑑定隨熱浸時間增加，於鋁化層中生成之介金屬相晶體結構。研究結果顯示，在熱浸10秒的鋁化層中，會於基材處形成六方晶τ5(H)-Al7Fe2Si之連續介金屬層，並且具有塊狀之立方晶τ5(C)-Al7(Fe,Cr)2Si相逐漸分離至鋁矽熔湯中。隨熱浸時間增加，τ5(C)-Al7(Fe,Cr)2Si相會以顆粒狀散布於τ5(H)-Al7Fe2Si連續介金屬層上方之鋁矽塗層中。當熱浸時間增加至180秒，可發現針狀之單斜晶τ6-Al4FeSi與正方晶τ4-Al3FeSi2介金屬相於具有散布τ5(C)-Al7(Fe,Cr)2Si顆粒之鋁矽塗層中形成。

A 5Cr-0.5Mo steel was coated by hot-dipping into a molten Al-10 wt.% Si bath at 700 ℃ for 10, 60, 120 and 180 seconds, respectively. Phase identification of the Fe-Al-Si intermetallic compounds formed in the aluminide layer during hot-dipping was carried out by using a combination of scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The results after a hot-dipping of 10 seconds showed that a hexagonal τ5(H)-Al7Fe2Si continuous layer formed adjacent to the steel substrate, while a lump of cubic τ5(C)-Al7(Fe,Cr)2Si phase floated in the Al-Si topcoat above the τ5(H)-Al7Fe2Si continuous layer. As the hot-dipping time increased, the lump transformed in shape into dispersive particles in the Al-Si topcoat above the τ5(H)-Al7Fe2Si continuous layer. After a hot-dipping of 180 seconds, monoclinic τ6-Al4FeSi and tetragonal τ4-Al3FeSi2 in needle shape were found in the Al-Si topcoat that contained the dispersive τ5(C)-Al7(Fe,Cr)2Si particles.