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Phase transformations in the Fe-8Al-5Ni-2C alloy, prepared by rapid solidification processing (RSP), have been studied by Choo and Kim. [1] They showed that the microstructure of the alloy in the as-solidified condition was austenite phase (␥) containing fine ordered L'l 2 -type precipitates. The formation of these fine ordered L'l 2 -type precipitates, lying along the ͗100͘ directions in the matrix, was attributed to the spinodal decomposition. It was also shown that, on aging at 823 K, the fine ordered precipitates grew and, at the same time, ␣(ferrite) and -carbide formed by a heterogeneous reaction at the ␥/␥ grain boundaries. With increasing aging time, the heterogeneous reaction became predominant, leading to a two-phase microstructure of ␣ and -carbide in the end. [1] Recently, we performed transmission electron microscopy (TEM) observations of the phase transformations in the Fe-8Al-5Ni-2C alloy, prepared by conventional casting process. It was found that the microstructure of the alloy in the as-quenched condition was austenite phase containing fine ordered L'l 2 -type precipitates, similar to the previous results for the as-solidified alloy. However, when the as-quenched alloy was aged at 823 K for a long time, the equilibrium microstructure was observed to be a mixture of (␣ ϩ B2 ϩ -carbide), rather than ␣ ϩ -carbide as reported by Choo and Kim.The alloy, Fe-8Al-5Ni-2C, was prepared in an air induction furnace by using 99.5 pct iron, 99.7 pct aluminum, 99.5 pct nickel, and pure carbon powder. After being homogenized at 1523 K for 12 hours under a protective argon atmosphere, the ingot was hot forged and then cold rolled to a final thickness of 2.0 mm. The sheet was subsequently solution heat treated at 1323 K for 2 hours and quenched into room-temperature water. The aging treatments were performed at 823 K for various times in a salt bath. The microstructures of the alloy were examined by means of optical microscopy and TEM. Thin foil specimens for TEM were prepared in a double jet electropolisher, using an electrolyte of 30 pct acetic acid, 60 pct ethanol, and 10 pct perchloric acid at 263 to 283 K. The current density was kept in the range from 1.5 to 2.0 ϫ 10 4 A/m 2 . Electron microscopy was performed on a JEOL* 2000FX scanning *JEOL is a trademark of Japan Electron Optics Ltd., Tokyo.transmission electron microscope (STEM) operating at 200 kV. Elemental distributions were examined using a LINK-AN 10000 energy-dispersive X-ray spectrometer

In the as-quenched condition, the microstructure of the Cu 2 MnAl alloy was L2 1 phase containing extremely fine L-J precipitates. This result is different from that reported by other workers in the asquenched Cu 2 MnAl alloy. When the as-quenched alloy was aged at 350 ЊC, ␥-brass precipitates started to appear within the L2 1 matrix. The orientation relationship between the ␥ -brass and the L2 1 matrix was determined to be cubic to cubic. This result is consistent with that observed by other workers in the aged Cu-Mn-Al alloy. When the alloy was aged at 460 ЊC, the ␥ -brass precipitates disappeared and platelike ␤ -Mn precipitates occurred within the L2 1 matrix. As the aging temperature was increased to 560 ЊC, the morphology of the ␤-Mn precipitates changed from platelike to granular shape. Electron diffraction examinations indicated that in spite of the morphology change the same orientation relationship between the ␤-Mn and the L2 1 matrix is maintained, and it could be best stated as follows: (210) ␤-Mn //(100) m , (120) ␤-Mn //(010) m , (001) ␤-Mn //(001) mThis result is in disagreement with that reported by Kuzobski et al. in the aged Cu 2 MnAl alloy. In their study, it was concluded that both the morphology of the ␤ -Mn precipitates and the orientation relationship between the ␤ -Mn and the L2 1 matrix would vary with the aging temperature.