DEFECTS IN Fe7C3 TYPE CARBIDE FORMED DURING THE CRYSTALLIZATION OF AMORPHOUS HIGH CARBON ALLOYS AND THEIR RELATION WITH THE AMORPHOUS STATE

M7C3 type carbides have an orthorhombic structure, as proposed by R. FRUCHART et al. This structure may be hidden by defects which are typical of the preparation method. In Fe7C3 formed by crystallization of sputter-deposited amorphous Fe75C25 alloys, the defects are only consistent with elongated domains whose size is less than [MATH] 100 A, the order of the defect size. In primary M7C3 carbides, present in white cast-iron and chromium steels, domains are about 100 times larger than in the latter case. Both results suggest that domain growth is impeded during the crystallization of amorphous Fe75C25. Nuclei may thus already exist in or be easily formed with a large density from the amorphous state. The formation of Fe7C3 is discussed within the frame of the GASKELL model.