銅-13.8鋁-7.0鎳合金相變化

Abstract

中 文 摘 要 在本論文中，我們利用掃描穿透式電子顯微鏡(STEM)以及X-光能量散佈儀(EDS)，研究銅-13.8wt%鋁-7.0wt%鎳三元合金的相變化。 當合金在淬火狀態下，其顯微結構為D03相的基地和極微細的析出物，根據實驗結果顯示，此微細析出物為L-J相。此外，由電子顯微鏡繞射分析顯示，L-J相會在D03基地中以兩個variants產生。當淬火合金在150℃時效處理後，其顯微結構為單一的D03相，隨著時效時間增加，我們發現D03相的domain尺寸有成長的趨勢；當時效溫度提高至200℃時，發現γ2相開始在D03的基地中析出。將溫度提升至450℃ 做短時間的時效處理，發現層狀的γ′麻田散相在基地中形成；當時效時間增加後，可觀察到極細微的B2 顆粒在γ′麻田散相內析出，這一實驗結果從未在銅-鋁-鎳三元合金中被其他學者所發現過；當時效時間再延長，發現球形的B2顆粒在α 基地相內和γ2 / α界面上生成，所以此合金在450℃的穩定相為(B2 +γ2 + α)。因此在450℃一連串的相變化為D03 àγ2 + γ′ 麻田散相àγ2 + B2 + γ′麻田散相àγ2 + B2 + α。當此合金在650℃至800℃做時效處理，可觀察到極微細的L-J相不只在基地相析出而且同時亦在γ2 /基地相界面上析出，且D03 domains 的形成是由於在淬火期間βàB2àD03的連續序化轉換而來的。此外，當合金時效溫度上升到850℃或更高做時效處理，發現合金的微結構為(D03+L-J), 在這條件下的顯微結構和淬火狀態是相似的，結果顯示合金的微結構在850℃或以上時為單一非序化β相。 基於以上結果，我們知道隨著溫度由150℃至850℃此合金的相變化為D03 à D03+γ2 à B2+γ2+α à γ2+β+L-J or γ2+B2 +L-J à β。

ABSTRACT In the present study, the phase transformations in the Cu-13.8wt%Al-7.0wt%Ni ternary alloy have been examined by means of scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectrometer (EDS). When the alloy was solution heat-treated at 1020℃ for 1 hour and then quenched into iced water rapidly, the microstructure of the alloy was D03 phase containing extremely fine precipitates. Transmission electron microscopy examinations indicated that the extremely fine precipitates are of the L-J phase. In addition, electron diffraction analyses indicated that the L-J precipitates have two variants within the D03 matrix. When the alloy was aged at 150℃, the microstructure of the alloy was single D03 phase and the D03 domains size was increased with increasing the aging time. However, when the aging temperature was increased to 200℃, the γ2 phase started to precipitate within the matrix. When the alloy was aged at 450℃ for short time, the lamellar γ′ martensite started to form within the matrix. With increasing aging time at 450℃, the extremely fine B2 particles occurred within the γ′ martensite. This result has never been found by other workers in the various Cu-Al-Ni ternary alloys before. After prolonged aging at this temperature, the spherical-shaped B2 particles were formed within the α matrix and on the γ2 / α interface. Thus, the phase transition sequence at 450℃ was found to be D03à γ2 + γ′ martensiteà γ2 + B2 + γ′ martensiteà γ2 + B2 + α. When the alloy was aged between 650℃ and 800℃, the extremely fine L-J particles could not only be observed within the matrix but also at the γ2 / matrix interface, and the D03 phase was formed by a βàB2àD03 continuous ordering transition during quenching. As the aging temperature was increased to 850℃ or above, the microstructure of the alloy was a mixture of (D03 + L-J) phases, which is similar to that observed in the as-quenched alloy. This result reveals that the microstructure of the alloy existing at 850℃ or above should be a single disordered β phase. Based on the experimental results, the phase transformation sequence as the aging temperature increased from 150℃ to 850℃ was found to be : (D03) à (D03 + γ2) à (B2 + α + γ2) à (γ2 + β + L-J) or (γ2 + B2 + L-J) à β.