Phase Transformations in a Cu-12.0Al-10.0Ni alloy
|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(TEM)和X光能量散佈分析儀(EDS)來研究觀察銅-12.0鋁-10.0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。在此值得一提的是我們利用TEM在淬火狀態下的試片觀察到a/4 <111>反相晶界，此結果極烈證明B2相區的存在，此特性從未被其他學者發現過。
當此合金在400℃施以短時間時效，其顯為結構變為2H-Martensite和α相之混合。同時，B2會以cuboid形狀在2H-martensite上析出，並以不規則之形狀在α相的基地上析出。當時效時間增加後，2H-martensite基地會漸漸消失而轉變成γ2，而B2則以cuboid的形狀在γ2基地上析出。因此，於400℃時合金之穩定顯微結構為(B2+γ2+α)之混合相。當此合金在500℃施以時效，其相變化情形與400℃時效相同。當時效溫度增加至600℃時，B2以片狀在α相上析出，而經過長時效處理後，α相區域變大，B2改以不規則形狀析出在α相上，另外在D03基地上亦有圓形的B2顆粒析出。因此600℃時，合金之穩定顯微結構為(B2+α+D03+L-J)之混合相。如果將時效溫度提高到700℃，則可觀察到a/4<111>APBs的成長，此時顯微結構為(B2+L-J+D03)之混合相。當時效溫度升高至925℃或以上時，則合金之顯微結構與淬火狀態相同，此結果顯示當時效溫度增加925℃以上，其穩定相為disordered β相。因此，將Cu-12.0Al-10.0Ni合金在400℃至1000℃溫度間時效處理，其相變化的過程為(B2 + α + γ2) à ( B2+ α + D03 + L-J) à B2 àβ。這種相變化過程從未被其他學者在Cu-Al-Ni合金中被發現過。|
Phase transformations in the Cu-12.0Al-10.0Ni alloy have been examined by means of optical microscopy (OM), scanning transmission electron microscopy (TEM), and energy-dispersive X-ray spectrometer (EDS). When the Cu-12.0Al-10.0Ni alloy was solution heat-treated and quenched, the microstructure of this alloy was D03 phase containing extremely fine L-J precipitates by using TEM. In the present alloy, we observe the a/4 <111> anti-phase boundaries. This result extremely demonstrates the existence of the B2 phase field, and it has never been found by other workers. As the alloy was aged at 400℃ for a short time, the morphology of B2 phase within the 2H-martensite phase and α phase are cuboidal-shaped and irregular-shaped, respectively. When the aging time was increased at this temperature, the 2H-martensite matrix was disappear and the matrix changed to γ2 phase. The morphology of B2 phase within the γ2 phase is cuboidal-shaped. Therefore, the stable microstructure of the alloy at 400℃ is (B2+ γ2 + α). As the alloy was aged at 500℃, the phase transformations of the alloy was the same as that isothermal heat-treated at 400℃. After increasing the aging temperature to 600℃, two kinds of precipitates, B2 and α, with a lamellar structure started to appear within the D03 matrix. After prolonged the aging time, the morphology of B2 phase within the α phase was transformed to irregular-shaped and α phase had been grown. Besides, the morphology of B2 phase within the D03 matrix is spherical-shaped. Therefore, the stable microstructure of the alloy at 600℃ is (B2+α+D03+L-J). A further increase in the aging temperature up to 700℃ resulted in a growth of the a/4<111>APBs could be observed. The microstructure of this time is (B2+L-J+D03). Progressively higher temperature aging and quenching experiments indicated that when the alloy was aged at 925℃ or above, the microstructure of the alloy was the same as that in the as-quenched condition. This result means that the microstructure of the alloy presented at 925℃ or above should be an disordered ferrite phase. Therefore, the Cu- 12.0 Al-10.0 Ni alloy with increasing aging temperature from 400℃ to 1000℃, the transformation sequence is (B2 + α + γ2) à ( B2+ α + D03 + L-J) à B2 àβ. This phase transition in Cu-Al-Ni alloys was never found by other workers.
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