MICROSTRUCTURAL CHARACTERIZATION OF A HIGH-CARBON FE-C ALLOY DURING ATTRITION MILLING AND SINTERING

Mechanical alloying of blended element 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 und er industrial conditions. Changes in the morphology and the microstruc tures 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. T he X-ray results are consistent with partial and complete amorphizatio n of bcc alpha-Fe and graphite, respectively, in the powder alloy afte r long milling times. Notwithstanding substantial carbon depletion in the alloy at long milling times, carbon solubility in alpha-Fe, calcul ated by measured peak shifts in the X-ray spectra, increases. Morpholo gically, longer milling times resulted in composite powder particles w ith smaller sires compared to those milled for shorter times, Conseque ntly, higher densities and hardness values were achieved for compacts attritor-milled at longer times, Undissociated carbon stripes alpha-Fe and pearlite phases exist in tbe compacts milled from powder blends a t shorter milling times; in contrast, irregular small patches of carbo n regions surround the alpha-Fe grains for powders milled at longer ti mes, Transmission electron microscopy revealed the presence of Fe3C in the alpha-Fe matrix of tbe sintered compact prepared from powders mil led for 20h.