銅－35錳－25鋁合金相變化

Abstract

在本論文中，我們利用穿透式電子顯微鏡（ＴＥＭ）和Ｘ-光能量散布分 析儀(EDS)來研究觀察Cu-35Mn-25Al合金之相變化。在淬火狀態下，合金 的顯微結構為 (L21+B2+L-J)之混合相。其中微細狀之B2相乃出現於L21之 區域內，此特徵從未被其他的學者所發現過。其中L-J相為一具有 orthorhombic結構之新相，其首先由劉增豐博士及鄭祥誠博士首度於 Cu2.2Mn0.8Al合金中[2]發現。當合金在300℃的溫度下做時效處理後，則 微細之B2顆粒會進行成長，且並未觀察到L-J相之存在。因此，於300℃時 合金之結構為(L21+B2)之混合相。當合金於500℃施以短時間之時效，則 B2之形狀由顆粒狀變化成針狀，其顯微結構仍為(L21+B2)相。然而，於此 溫度下並將時效時間增加後，γ-brass 與β-Ｍｎ兩類型之析出物開始於 晶界之上出現。於此溫度下做長時間之時效後，整個合金之顯微結構將成 為（γ-brass＋β-Ｍｎ）之混合。因此，於500℃時合金之穩定顯微結構 為（γ-brass＋β-Ｍｎ）相。 γ-brass與β-Ｍｎ析出物之共存從未被 其他學者於Cu-Mn-Al合金中發現過。如果將時效溫度提高至650℃，則β- Ｍｎ析出物將在L21 母相中迅速成長，且無γ-brass析出物被觀察到。當 時效溫度升高至680℃或以上時，則合金之顯微結構與淬火狀態相同。 Phase transformations in the Cu-35Mn-25Al alloy have been investigated by using transmission electron microscope (TEM) and energy-dispersive X-ray spectrometer (EDS). In the as-quenched condition, the microstructure of the alloy was a mixture of ( L21+B2+L-J ) phases. The B2 phase with a fine particle shape was present within L21 domains. This feature has never been observed by other workers.The L-J phase is a new phase having an orthorhombic structure, which was found firstly by T. F. Liu and S. C. Jeng in a Cu2.2Mn0.8Al alloy.[2]When the alloy was aged at 300℃, the fine B2 particles grew and no evidence of the L-J phase could be detected. Therefore , the microstructure of the alloy at 300℃is a mixture of ( L21+B2 ) phases. When the alloy was aged at 500℃for short times, the shape of the B2 particles changed from particle into needle-like. The microstructure is still ( L21+B2 ) phases. However, when the aging time wasincreased at this temperature, two kinds of precipitates, namely γ- brass andβ- Mn, started to appear on the grain boundary. After prolonged aging at thistemperature, the grain boundary precipitation of(γ- brass + β- Mn) became predominant . Therefore, the stable microstructure of the alloy at 500℃is (γ- brass + β- Mn).The coexistence of the γ- brass and β- Mn precipitates has never been observed by other workers in the Cu- Mn-Al alloys. A further increase in the aging temperature up to 650℃ resulted in a rapid growth of theβ- Mn precipitates within L21 matrix and no γ- brass precipitates could be observed. Progressively higher temperature aging and quenching experiments indicated that when the alloy was aged at 680℃or above, the microstructure of the alloy was the same as that in the as-quenched condition.