| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 90 === 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.
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