Swelling behavior in reactive sintering of Fe–Al mixtures

Sintering is generally recognized as a consolidation process of the powder compacts. However, the swelling problem is always observed in a stress-free reactive sintering of iron–aluminum elemental powder mixtures. Present study on the stress-free vacuum sintering of Fe–29 at.% Al (for sintered Fe 3Al) compacts indicated that the transitory appearance of an intermediate phase, Fe 2Al 5, attributed to this swelling behavior. Further study on the Fe–71.5 at.% Al (for sintered Fe 2Al 5) compacts shows that a large and rapid increase of the specimen’s dimension occurred during a low temperature sintering process, meantime, a sponge-like porous microstructure was obtained. An in situ temperature variation was monitored on these Fe–Al compacts, and a violent and rapidly exothermic heat was found. Compared with the thermal behavior of Ni–Al compacts, it is suggested that many simultaneous fast reactions have occurred inside the Fe–Al mixture during sintering and cause the swelling phenomenon.