Microstructural characterization of a high carbon Fe-C alloy during attrition milling and sintering

Mechanical alloying of blended elemental powders of composition Fe-5w/oC was carried out in a heavy duty attritor for milling times of 1.5,10,20 and 30h followed by compaction, sintering and furnace cooling under industrial conditions. Changes in the morphology and the microstructures of the as-milled powders and the compacts were characterized by laser diffraction size analysis, x-ray diffractometry and transmission electron microscopy. Carbon content was measured by C-S techniques. The X-ray results are consistent with partial and complete amorphization of bec α-Fe and graphite, respectively, in the powder alloy after long milling times. Notwithstanding substantial carbon depletion in the alloy at long milling times, carbon solubility in α-Fe, calculated by measured peak shifts in the X-ray spectra, increases. Morphologically, longer milling times resulted in composite powder particles with smaller sizes compared to those milled for shorter times. Consequently, higher densities and hardness values were achieved for compacts attritor-milled at longer times. Undissociafed carbon stripes, α-Fe and pearlite phases exist in the compacts milled from powder blends at shorter milling times; in contrast, irregular small patches of carbon regions surround the α-Fe grains for powders milled at longer times. Transmission electron microscopy revealed the presence of Fe₃C in the α-Fe matrix of the sintered compact prepared from powders milled for 20h.