鐵鋁鈦合金相變化

Abstract

中文摘要 本論文利用光學顯微鏡，掃描穿透式電子顯微鏡和X光能量散佈分析儀等，研究觀察不同之鋁及鈦含量對鐵-鋁-鈦三元合金顯微結構組織的影響。本論文所得到的具體研究結果如下: (一)、當鐵-20 at.%鋁-8 at.%鈦合金經固溶處理後在1000˚C做時效處理一小時急速淬火後，其顯微結構為A2、D03與C14 之混合相。利用穿透式電子顯微鏡及擇區繞射技術，C14與(A2+D03) 基地之間的方向關係為: ( )C14//( )m , ( )C14//( )m , ( )C14//( )m 此方向關係至今從未被其他學者在鐵-鋁-鈦合金系統中發現過。 (二)、當鐵-23 at.%鋁-8.5 at.%鈦合金在固溶處理並急速淬火後，其顯微結構為A2與D03之混合相。其中A2與D03相是在淬火過程中經由A2 →B2→(A2+D03) 規律化變態所形成的。利用穿透式電子顯微鏡檢驗發現當此合金在900˚C做時效處理時，D03區域尺寸大小會隨著時效處理時間增長而變大，並且在a/2<100>反向晶界其顯微結構之變化依序為：A2 → (A2+D03) → (B2+D03)。此現象至今從未被其他學者在鐵-鋁-鈦合金系統中發現過。 (三)、在淬火狀態下，鐵-24.6 at.%鋁-7.5 at.%鈦合金的淬火顯微結構為A2與D03之混合相。當此合金在900˚C適當時間之時效處理後，發現D03區域成長，並且B2相會開始沿著a/2<100>反向晶界析出。隨著時效時間的增加，D03 → (B2+D03*)相分離的現象開始發生在a/2<100>反向晶界，並且持續相分離到先前完整的D03區域。此微觀結構的變化至今從未被其他學者在鐵-鋁-鈦合金系統中發現過。 (四)、在淬火狀態下，鐵-23 at.%鋁-7 at.%鈦合金的淬火顯微結構為A2與D03之混合相。當此合金在800˚C適當時間之時效處理後，D03區域會沿著<100>特定方向成長，並且極細微B2顆粒會開始在a/2<100>反向晶界上析出。隨著時效時間的增加，B2顆粒將會成長直到佔據整個a/2<100>反向晶界。因此合金在800˚C做時效處理後其穩定顯微結構為B2與D03之混合相。此B2與D03形成的微觀結構發展現象至今從未被其他學者在鐵-鋁-鈦合金系統中發現過。 (五)、在淬火狀態下，鐵-20 at.%鋁-8 at.%鈦合金的淬火顯微結構為A2與D03之混合相。此合金在750˚C至1100˚C溫度範圍內做時效處理後其微觀結構之變化依序為：A2+D03→A2+D03+C14 →B2+C14→A2+C14→A2。

Abstract Effects of the aluminum (Al) and titanium (Ti) contents on the phase transformations of the Fe-Al-Ti ternary alloys have been investigated by means of optical microscopy, scanning transmission electron microscopy and energy-dispersive X-ray spectrometry. On the basis of the experimental examinations, the results obtained follows: [1]. When the Fe-20at.%Al-8at.%Ti alloy was aged at 1000˚C for 1 h and then quenched, the microstructure of the alloy was a mixture of (A2+D03+C14) phases. By means of transmission electron microscopy and diffraction technique, the orientation relationship between the C14 precipitate and (A2+D03) matrix was determined as follows: ( )C14//( )m , ( )C14//( )m , ( )C14//( )m. The present result of the orientation relationship has never been reported by previous workers in the Fe-Al-Ti alloy systems before. [2]. The as-quenched microstructure of the Fe-23 at.% Al-8.5 at.% Ti alloy was a mixture of (A2+D03) phases. Transmission electron microscopy (TEM) examinations indicated that when the alloy was aged at 900˚C, the size of the D03 domains increased with increasing the aging time, and an A2 → (A2+D03) → (B2+D03) transition occurred at a/2<100> anti-phase boundaries (APBs). This feature has never been reported by other workers in the Fe-Al-Ti alloy systems before. [3]. The as-quenched microstructure of the Fe-24.6 at.% Al-7.5 at.% Ti alloy was a mixture of (A2+D03) phases. When the alloy was aged at 900˚C for moderate times, the D03 domains grew considerably and B2 phase appeared on a/2<100> anti-phase boundaries (APBs). With continued aging at 900˚C, phase separation from prior-D03 to (B2+D03*) occurred initially on a/2<100> APBs, and then proceeded toward the whole prior-D03 domains. This microstructural revolution has never been reported by other workers in the Fe-Al-Ti alloy systems before. [4]. The as-quenched microstructure of the Fe-23 at.% Al-7 at.% Ti alloy was a mixture of (A2+D03) phases. When the as-quenched alloy was aged at 800˚C for moderate times, the D03 domains grew preferentially along <100> crystallographic directions and extremely fine B2 particles started to occur at a/2<100> anti-phase boundaries (APBs). After prolonged aging at 800˚C, the B2 particles would grow to occupy the whole a/2<100> APBs. Consequently, the stable microstructure of the alloy at 800˚C was a mixture of (B2+D03) phases. The microstructural development for the formation of the (B2+D03) phases has never been reported in Fe-Al-Ti alloy systems before. [5]. As-quenched microstructure of the Fe-20 at.% Al-8 at.% Ti alloy was a mixture of (A2+D03) phases. When the as-quenched alloy was aged at temperatures ranging from 750˚C to 1100˚C, the phase transition sequence as the aging temperature increased was found to be A2+D03→A2+D03+C14→B2+C14→A2+C14→A2. It is noted here that the phase transition has never been observed by other workers in the Fe-Al-Ti alloys before.