Microstructure and phase composition of an alloy of iron and chrome disilicides

The phase composition, microstructure, and interphase interfaces of the disordered CrSi$_2$–FeSi$_2$ solid solution obtained by spontaneous crystallization (before and after annealing) have been investigated by scanning, transmission electron microscopy, electron diffraction, and X-ray energy dispersive spectrometry. The as-grown samples contained the phases of CrSi$_2$ with the P 6$_4$22 hexagonal structure and FeSi$_2$ with the P 4/mmm tetragonal structure. Annealing of the samples led to the phase transformation of tetragonal FeSi$_2$ into the orthorhombic modification Cmca. Precipitates of cubic iron monosilicide FeSi with space group P 213, nano-precipitates of Si and silicon silicide Cr$_5$Si$_3$ with a tetragonal structure I4/mcm were observed inside the FeSi$_2$ grains. Impurities of interstitial Cr atoms with a concentration up to 2.0 at% are found in iron (di)silicides grains in all samples. The structure of the CrSi$_2$ phase remains unchanged after annealing; the concentration of impurity iron atoms is about 0.7 at%. Orientation relationships between the crystal lattices of the phases are established and strains due to the mismatch of the crystal lattices are determined.