On the parameters affecting the formation of iron aluminides during pressure-assisted infiltration of aluminium into a preform of steel fibres

The parameters affecting the formation of iron aluminides during reactive infiltration of iron-based fibre preforms in a squeeze-casting equipment were investigated. The volume fraction of intermetallic phases was found to increase when the fibre volume fraction and size decreased. The increase of the temperatures of the die, aluminium and preform allowed avoiding premature chocking of the preforms, reducing the gradient of reaction and increasing the extent of exothermic reactions. As-infiltrated material with overall chemical composition corresponding to Fe3Al was studied by SEM, X-ray diffraction and TEM. The unreacted iron fibres were surrounded by iron-rich FeAl phases. The single-phase grains adjacent to the boundary layer were identified as Fe2Al5 whereas the grains with lamellar morphology were identified as consisting of a mixture of FeAl and FeAl2 lamellae. Heat treatment of such an as-infiltrated material resulted in the formation of a fine-grained structure composed of FeAl and Fe3Al phases.