本論文研究四元Fe-34 Ni-4.5 Al-1.1 C (wt.%)合金經1100oC固溶處理與再經低溫恆溫處理後的微觀結構改變與所對應之相變化。固溶處理後，為單一FCC結構之沃斯田體相(γ)；將固溶處理後之合金做恆溫處理，合金的相變化如下：於600oC至1000oC的區間，觀察到為B2相析出，合金在固溶處理後得到過飽和固溶體，經恆溫處理，無序的過飽和固溶體在有序化反應之後，形成有序的B2相，隨後經析出相變化生成富鎳鋁之B2析出物，反應式為γ → γ′ + BCC → γ′ + B2。另外500oC到700oC有κ-碳化物之析出，κ-碳化物是由沃斯田體(γ)相由高溫冷卻過程發生spinodal相分離成低溶質(γ′)與高溶質相(γ″)，高溶質相(γ″)於更低溫經過有序化反應而轉變為κ-碳化物，接著由析出相變化形成κ-碳化物，其總反應式為：γ → γ′ + γ″ → γ′ + κ-碳化物，並在溫度500oC和550oC時，會在合金晶界處發現有層狀析出物。層狀反應之形式如下：γ → γ′ + γ″ → γ′ + κ-碳化物→ lamellar γ′ + lamellar κ-碳化物。

Phase transformations and microstructure changes of an Fe-34 Ni-4.5 Al-1.1 C (wt.%) alloy have been studied through solution treatment at 1100oC and following annealing at different low temperatures. The results show that the alloy exhibits a single FCC structure austenite phase after solution treatment. We acquired the supersaturated solid solution after solution treatment. Upon annealing the sample at temperature ranging from 600oC to 1000oC, disordered supersaturated solution transformed to ordered B2 phase after ordering reaction. Hence, the B2 phase rich in Ni and Al appeared through precipitation transformation. The reaction can be written as following: γ → γ′ + BCC → γ′ + B2. Upon cooling from high temperature, we observed spinodal decomposition takes place i.e., the austenite phase(γ) transformed into solute-lean austenite (γ′) and solute-enriched austenite (γ″). The solute-enriched austenite phase transformed into κ-carbides from 500oC to 700oC. Hence, κ-carbides appeared through the precipitation transformation. The reaction can be written as follows: γ → γ′ + γ″ → γ′ + κ-carbides. On the other hand, the lamellar form of precipitates could be observed at the grain boundary at 550oC and 500oC. The cellular reaction can be written as follows: γ → γ′ + γ″ → γ′ + κ-carbides→ lamellar γ′ + lamellar κ-carbides.

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