鐵-8鋁-12鎳-2碳合金之相變化

Abstract

我們使用光學顯微鏡、掃描式穿透電子顯微鏡和X光能量散佈分析儀來研究鐵-8.0鋁-12.0鎳-2.0碳合金的相變化。 在鐵-8.0鋁-12.0鎳-2.0碳合金經過固溶和淬火後，此合金的微結構是沃斯田鐵和微細κ´碳化物相的混和，其中微細的κ´碳化物相是在淬火過程中以史賓諾多節點分解反應（Spinodal Decomposition）產生，具有L´12結構。 當合金在550℃到750℃的溫度區間進行時效，經由穿透式電子顯微鏡的檢驗來得知此溫度區間的肥粒鐵相、B2相、和κ碳化物相穩定結構可以保持到750℃；當合金在850℃時效然後淬火，粗的和細的B2顆粒可以在肥粒鐵基地內觀察到，而它們是分別經由時效過程和淬火過程形成的。而在950℃時效時，粗的κ碳化物和細的κ´碳化物也可以同時在沃斯田鐵基地上被觀察到，我們也發現有經由淬火過程時α→B2有序轉換產生的細微a/2<111>反相晶界。當合金在1050℃時效時，其穩定結構是沃斯田鐵相和肥粒鐵相，然而在1150℃或更高的溫度是沃斯田鐵單相，這個相轉換過程之前不曾被其他研究者在鐵-鋁-鎳-碳合金中發現過。

Phase transformations in the Fe-8Al-12Ni-2C alloy have been examined by means of optical microscopy (OM), scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectrometer (EDS). When the Fe-8Al-12Ni-2C alloy was solution heat-treated and quenched, the microstructure of Fe-8Al-12Ni-2C alloy was a mixture of (γ＋κ'-carbides). When the alloy was aged at the temperatures from 550℃ to 750℃, transmission electron microscopy examinations revealed that the stable microstructure of (α+ B2+κ-carbide) could be preserved up to 750℃. When the alloy was aged at 850℃ and then quenched, both the coarse and the fine B2 particles could be observed within the ferrite matrix. The coarse and the fine B2 particles were formed during the aging process and the quenching process, respectively. When the alloy was aged at 950℃, both the coarse κ-carbide and the fine κ'-carbides were formed by spinodal decomposition during quenching. We also found that the fine B2 domains with a/2<111> anti-phase boundaries were formed during quenching by αàB2 ordering transition. When the alloy was aged at 1050℃, the stable microstructure in the present alloy was austenite and ferrite phase. The microstructure of the alloy at 1150℃ or above is a single austenite phase. Other workers in the Fe-Al-Ni-C alloys before have never reported this transition.