鎳含量對銅鋁鎳合金相變化之影響

Abstract

本論文利用掃描穿透式電子顯微鏡和X光能量散佈分析儀等，研究觀察不同之鎳含量對銅－鋁－鎳三元合金顯微結構的影響。 本論文所得到的具體研究成果如下： (一)、在淬火狀態下，銅– 14.2鋁– 7.8鎳合金的顯微結構為D03和極細微之L-J混合相。當此合金在500℃做短時間時效處理後，γ2顆粒會開始在D03基地中析出，而餘留的基地會在淬火過程中經由麻田散相變化轉變成γ1'麻田散相。然而，在500℃延長時效時間，這些餘留的D03基地會變態成 (α + B2 析出物) 相。當此合金在150℃至750℃之間做時效處理時，所產生的相變化反應依序為：D03 → (D03 + γ2) → (γ2 + α + B2 析出物) → (β + γ2) → β。此相變化反應與其他學者在銅-鋁-鎳合金中所觀察的截然不同。 (二)、在淬火狀態下，銅– 14.2鋁– 9.0鎳合金的顯微結構為D03和極細微之L-J混合相。在500℃時效的初期，可觀察到高密度而細小的B2析出物在層狀結構的γ1'麻田散相中析出，其中γ1'麻田散相是在淬火過程中經由D03 → γ1' 麻田散相變化所產生的。隨著時效時間的增加，在500℃的恆溫相變態反應依序為：D03 → (D03 + B2 析出物) → (D03 + α + B2 析出物) → (α + γ2 + B2 析出物)，此相變態反應從未被其他學者所發現過。此外，在B2析出物和α相之間可同時觀察到Kurdjumov-Sachs和Nishiyama- Wassermann這兩種方向關係。 (三)、在淬火狀態下，銅– 14.2鋁– 12.0鎳合金的淬火顯微結構為D03和極細微之L-J混合相，其中D03相是在淬火過程中經由A2 → B2 → D03連續規律化相變態所形成。在本研究中可清楚觀察到a/4<111>反相晶界，此處值得特別一提的是，至今a/4<111>反相晶界從未被其他學者在銅-鋁-鎳合金系統中發現過。由於a/4<111>反相晶界的存在，本論文亦直接證實了在銅-鋁-鎳合金中的連續規律化變態為A2 → B2 → D03，而並非有些學者所提的A2 → D03。這結果從未被其他學者所發現。此外，同時證實鎳添加在銅– 14.2鋁合金中會提高B2 → A2的相轉移溫度。 (四)、當銅– 14.2鋁– 15.0鎳合金在固溶處理後急速淬火，其顯微結構亦為 (D03 + L-J) 混合相。由於伴隨著十分微小D03 相的a/2<100>反相晶界和伴隨著細小B2相的a/4<111>反相晶界均可被觀察到，所以我們推斷在淬火狀態下的D03相是在淬火過程中以A2 → B2 → D03連續規律化相變態所形成。此合金在400℃至1000℃溫度範圍內做時效處理後，其顯微結構之變化依序為：(α + B2 析出物) → (B2 + B2析出物) → B2 → A2。值得注意的是在本研究中並未發現有γ2相存在。

The effects of the nickel content on the phase transformations of the Cu-Al-Ni ternary alloys have been investigated by means of scanning transmission electron microscopy and energy-dispersive X-ray spectrometry. Based on the examinations, some results can be summarized as follows: [1].In the as-quenched condition, the microstructure of the Cu – 14.2 wt. % Al – 7.8 wt. % Ni alloy was D03 phase containing extremely fine L-J precipitates. When the alloy was aged at 500℃ for short times and then quenched, γ2 particles started to precipitate within the D03 matrix at the aging temperature and the remaining D03 matrix would transform to γ1' martensite during quenching. However, after prolonged aging at 500℃, the remaining D03 matrix would transform to a mixture of (α + B2 precipitate) phases. When the as-quenched alloy was aged at temperatures ranging from 150℃ to 750℃, the phase transformation sequence as the aging temperature increased was found to be D03 → (D03 + γ2) → (γ2 + B2 precipitate + α) → (β + γ2) → β. It is noted that this transformation is quite different from that observed by other workers in the various Cu-Al-Ni alloys. [2].In the as-quenched condition, the microstructure of the Cu – 14.2 wt. % Al – 9.0 wt. % Ni alloy was D03 phase containing extremely fine L-J precipitates. During the early stage of isothermal aging at 500℃, a high density of fine B2 precipitates was observed within the extremely thin lamellar γ1' martensite, where the γ1' martensite was formed by a D03 → γ1' martensitic transformation during quenching. With increasing aging time at 500℃, the phase transition sequence was found to be D03 → (D03 + B2 precipitate) → (D03 + α + B2 precipitate) → (α + γ2 + B2 precipitate). Besides, both Kurdjumov- Sachs (K-S) and Nishiyama-Wassermann (N-W) orientation relationships between the B2 precipitate and the α phase could be detected in the aged alloy. [3].The as-quenched microstructure of the Cu – 14.2 wt. % Al – 12.0 wt. % Ni alloy was D03 phase containing extremely fine L-J precipitates, where the D03 phase was formed by an A2 → B2 → D03 continuous ordering transition during quenching. The a/4<111> anti-phase boundaries (APBs) have never been found by other workers before. The presence of the a/4<111> APBs strongly confirms that the D03 phase existing in the as-quenched alloy was formed by an A2 → B2 → D03 ordering transition during quenching, rather than A2 → D03 transition reported by other workers. Besides, the addition of nickel to the Cu– 14.2 wt. % Al binary alloy would raise the B2 → A2 transition temperature. [4].When the Cu – 14.2 wt. % Al – 15.0 wt. % Ni alloy was solution heat-treated and then quenched, the microstructure was D03 phase containing extremely fine L-J precipitates. Since both fine D03 domains with a/2<100> APBs and small B2 domains with a/4<111> APBs could be observed, the D03 phase existing in the as-quenched alloy should be formed by an A2 → B2 → D03 continuous ordering transition during quenching. With increasing the aging temperature from 400℃ to 1000℃, the phase transformation sequence was found to be (α + B2 precipitate) → (B2 + B2 precipitate) → B2 → A2. It is worthwhile to note that no evidence of the γ2 phase could be detected in the alloy.