Phase transformations of mechanically alloyed Fe-Cr-P-C powders
Abstract Fe 77 Cr 4 P 8 C 11 alloy was prepared by mechanical alloying (MA) of elemental Fe, Cr, P and C (graphite) powders in a planetary ball mill type Fritsch P7 under argon atmosphere. Morphological changes, microstructural and structural evolutions during ball milling were followed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and 57 Fe Mossbauer spectrometry (MS) as a function of the milling time. The crystallite size refinement against the milling time is accompanied by an increase of the atomic level strain. After 6 h of milling, the dissolution of phosphorous into the α-Fe matrix is evidenced by the formation of a small amount (∼4%) of the paramagnetic Fe 2 P phase as revealed by Mossbauer spectrometry. The complete mixing of all the elemental powders at the atomic level is achieved at 12 h of milling and results, after 24 h, in an amorphous matrix where nanocrystalline phosphides and carbides with nearly equal crystallite sizes are embedded. Further milling time up to 190 h gives rise to the formation of both the orthorhombic and the hexagonal (FeCr) 7 C 3 carbide as well as the superparamagnetic ɛ′-Fe 2.2 C carbide through the recrystallisation of the amorphous phase.