銅-17.0鋁-10.0鎳合金相變化

Abstract

摘 要 在本論文中，我們利用光學顯微鏡(OM)、掃描穿透式電子顯微鏡(STEM)以及X-光能量散佈分析儀(EDS)，研究銅-17.0 wt. % 鋁-10.0 wt. % 鎳合金的相變化。此合金在淬火狀態下的顯微結構為(D03 + L-J)相之混合，而D03相是在淬火過程中經由序化反應所形成。 當此淬火合金在150℃時效處理後，僅有單一的D03相被發現，相較於淬火狀態下此D03相的尺寸有成長的現象。當時效溫度提高至350℃做長時間的時效處理，可以發現D03相的尺寸有成長的趨勢，但是L-J析出物的尺寸依舊沒有改變。當在400℃做短時間的時效處理，可觀察到高密度且細小的B2顆粒在γ2相以及層狀的γ1′麻田散相基地中析出，其中γ1′麻田散相是在淬火期間經由D03 à γ1′麻田散相變化所產生；若在400℃進一步延長時效時間，可以觀察到B2顆粒成長，而剩餘的D03基地會轉變成(α + γ2)相，所以此合金在400℃的穩定相為(B2 + γ2 + α)相之混合。當時效處理溫度提升到600℃或以上時，發現合金的顯微結構與淬火狀態下之顯微結構相同，為(D03 + L-J)之混合相，其中D03相是經由序化反應所產生的。這個結果顯示此合金在600℃以上的顯微結構為單一B2相，這與其他學者在銅-14鋁-10鎳合金中所觀察到的不同。值得注意的是，當我們利用熱差分析儀(DTA)進行分析時，發現在950℃左右有吸熱現象，因此我們推測在此時有B2 à β序化-非序化相變化發生。

ABSTRACT Phase transformations in the Cu-17.0 wt. % Al-10.0 wt. % Ni alloy have been examined by means of optical microscopy, scanning transmission electron microscopy and energy- dispersive X-ray spectrometry. In the as-quenched condition, the microstructure of the present alloy was fine D03 phase containing extremely fine L-J precipitates, where the fine D03 phase was formed by an ordering transition during quenching. When the alloy was aged at 150℃ and then quenched, only coarsened D03 domains could be observed. When the alloy was aged at 350℃ for longer times, the size of the D03 domains was increased but the size of the L-J precipitates was independent of the aging time. When the aging temperature was increased to 400℃, a high density of fine B2 precipitates started to appear within the cuboidal γ2 phase and lamellar γ1' martensite, where the γ1′ martensite was formed by a D03 à γ1′ martensitic transformation during quenching. After prolonged aging at this temperature, the B2 precipitates grew and the remaining D03 matrix would transform to (α + γ2) phases. Therefore, the stable microstructure of the alloy at 400℃ was the mixture of (B2 + γ2 + α) phases. As the aging temperature was increased to 600℃ or above, the microstructure of the present alloy was fine D03 phase containing extremely fine L-J precipitates, which was the same as that observed in the as-quenched alloy. This result reveals that the microstructure of the present alloy existing at 600℃ or above should be a single B2 phase. This result is different from that observed by other workers in the Cu-14 wt. % Al- 10 wt. % Ni alloy. It is worthwhile to mention that an endothermic reaction was found at a temperature about 950℃ using differential thermal analysis during heating. This indicates that a B2 à β order-disorder transformation was occurred at this temperature.