Processing of iron aluminides by pressureless sintering through Fe+Al elemental route

The sintering behavior of elemental powders of Fe and Al was investigated at various heating rates by dilatometric experiments in the temperature range of 1000–1350 °C. It was found that the formation of FeAl was accompanied by expansion due to volume change during the formation of the intermediate phase Fe2Al5. The mechanism of FeAl formation and the final density depended on the heating rate. The expansion rate during slow heating (≤0.5 °C min−1) was 0.0018 mm mm−1 per min as against ∼0.34 mm mm−1 per min at high (≥1°C min−1) heating rates. Slower heating rates (≤0.5°C min−1) lead to lower expansion during Fe2Al5 formation and subsequently to a higher density of FeAl up to 94.5% of theoretical. This is the highest density obtained so far (during the last 25 years) by heating elemental Fe and Al powders without pressure assistance to form FeAl or any other intermetallic in the Fe–Al system. The sequence of phases formed during the heating of Fe+Al mixture was identified by X-ray diffraction, optical microscopy and SEM. The results, along with the DSC data were correlated to the expansion and shrinkage behavior of the samples.