鐵鋁錳碳和鐵鋁錳碳矽合金相變化

Abstract

本論文利用光學顯微鏡(OM)，X光能量分佈儀(EDS)以及掃描穿透式電子顯 微鏡(STEM)等，研究鐵-8.5鋁-4.5鎳-1.6碳合金之相變化。本論文所得的 結果如下:此合金在淬火狀態下，其顯微結構為沃斯田鐵相＋細微的κ相 碳化物。其中κ相碳化物乃是在淬火過程中於沃斯田鐵相基地內以節點分 解(Spinodal Decomposition)變態形成。這與其它鐵鋁錳碳合金研究者所 發表不同。當此合金在550℃作時效處理後，我們發現淬火狀態下的細微 κ相碳化物沿著<100>方向成長。另外，當增長時效處理後，在晶界產生 了γ←κ＋α的分解反應；時效處理時間再增長後，亦可觀察到球狀的B2 相顆粒在肥粒鐵相中析出，而產生了γ←(κ＋α)← (κ＋B2＋α)的相 分解反應κ相碳化物和(B2＋α)相之方向關係為 (111)κ相//(110)(B2＋ α) [110]κ相//[001](B2＋α)此研究所觀察到的B2相,鐵-鋁-碳、鐵- 鋁-錳-碳、鐵-鋁-鎳-碳和鐵-鋁-(錳，鎳)-碳合金系統內從未被其它學者 所觀察過。 The microstructures of five austenitic Fe-Al-Mn-C-(Si) The microstructure of an Fe-8.5Al-4.5Ni-1.6C alloy, prepared by conventional casting, has been investigated by using optical microscopy (OM), transmission electron microscopy (TEM) and energy- dispersive X-ray spectrometer (EDS). In the as-quenched condition, the microstructure of the present alloy was austenite phase containing (Fe,Ni)3AlC carbides (k'-carbide). The k' -carbides having an L'12-type structure were formed within the austenite matrix during quenching by spinodal decomposition. This feature is quite different from that observed by other workers in various Fe-Al-Mn-C alloys. When the present alloy was aged at 550 C for short times, fine k'- carbides existing in the as-quenched alloy had grown along <100> directions, and no precipitates could be detected on the grain boundary. However, prolonged the aging time at 550 C, coarse (Fe,Ni)3AlC carbides ( k-carbide ) started to appear on the grain boundaries. Subsequently, these coarse k-carbides grew into the adjacent grains through a y □+ k-carbide transition. With further aging at 550 C, a spherical B2-type particles were started to form within the ferrite region. The orientation relationship between k-carbide and (□+ B2) phases was determined to be (111)k-carbide // (110)□B2, and [110]k- carbide// [001](□B2). Consequently, the phase decomposition of y ( □+ k-carbide ) ( □+ B2 + k- carbide ) would continue to occur during aging , and finally the stable microstructure of the present alloy aged at 550 C should be a mixture of Widmanstdtten-like k-carbide, ferrite phase and spherical B2- type precipitates dispersing within the ferrite phase. It is noted here that the B2 phase has never been observed by other workers in various Fe-Al-C, Fe-Al-Mn-C, Fe-Al-Ni-C and Fe-Al-( Mn,Ni)-C alloys.