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Two Fe–Mn–Al alloys with compositions of Fe–23.0 wt.% Mn–7.4 wt.% Al–0.03 wt.% C (alloy A) and Fe–28.5 wt.% Mn–8.8 wt.% Al–0.09 wt.% C (alloy B) were studied throughout the quenching and aging process. After the specimens were heated at 1050 °C for 1 h, and then quenched in room temperature water, both alloys have a small amount of austenite distributed randomly along the ferrite grain boundary. In the TEM study, alloy B shows D 0 3 precipitates exist within the ferrite grains while alloy A does not. Samples in alloy B were heated at 1050 °C for 1 h, and then quenched directly into a salt bath at lower temperatures. The upper-limit temperature for the existence of the D 0 3 phase in the ferrite matrix for alloy B is between 500 and 510 °C. After quenching alloy A from 1050 °C and aging at temperatures below 430 °C, we observed that the D 0 3 phase precipitated homogeneously inside the ferrite grains. This result is consistent with the classical nucleation and growth mechanism of D 0 3 precipitates growing within the ferrite matrix. The upper limit temperature for the existence of the D 0 3 phase in the ferrite grains of alloy A is between 430 and 440 °C. Measuring the Al contents in the ferrite grains of these alloys, we found that the 14.5 at.% Al in the ferrite grains of alloy A is, so far, the lowest Al content yielding the possible existence of a D 0 3 phase in both binary Fe–Al and ternary Fe–Mn–Al alloys. |
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