| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 90 === Phase transformations in Fe- 8.0 wt. % Al -28.5 wt. % Mn alloy with 5.0 and 10.0 wt. % Cr have been investigated by means of optical microscopy, scanning transmission electron microscopy and energy-dispersive X-ray spectrometey. In the as-quenched condition, the microstructure in the Fe- 8.0 wt. % Al- 28.5 wt. % Mn-5.0 wt. % Cr alloy was a (ferrite) + g (austenite) duplex phases and only single a phase could be found in the Fe- 8.0 wt. % Al- 28.5 wt. % Mn-10.0 wt. % Cr alloy. When the Fe- 8.0 wt. % Al- 28.5 wt. % Mn-5.0 wt. % Cr alloy was aged at various temperatures, no precipitates could be found within the austenite matrix. However, different kinds of precipitates could be formed within the ferrite grains with increasing the aging temperature. When both alloys were aged at temperatures ranging from 350°C to 450℃, both ordered D03 and A12 α-Mn phases could be observed within the ferrite matrix. In addition to the D03 and A12 a-Mn phases, A13 b-Mn precipitates could also be found in both alloys aged at higher temperatures. In these two alloys, the phase transformation sequences in the ferrite grains as the aging temperature increased were found to be (α + A12 α-Mn + D03) → (α + A12 α-Mn) → (α + A13 β-Mn) → α. In spite of having the same microstructural developments in these two alloys, experimental results indicated that the existing temperatures of both the D03 and A12 a-Mn phases were increased with increasing the Cr content.
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