On the control of the residual porosity in iron aluminides processed by reactive squeeze-infiltration of aluminium into a preform of steel fibres

An original approach for the synthesis of iron aluminides of the type FeAl1−x is presented, based on the use of a squeeze-casting equipment for inducing the reactive infiltration of Al into a porous preform made by sintering continuous Fe-based fibres. The casting is subsequently homogenised by heat treatment in the solid state. Preforms with fibre volume fractions ranging between 40 and 80% (fractions that correspond to stoichiometries close to FeAl and Fe3Al, respectively) are prepared using steel-wool fibres with various diameters. Small fibre diameters and high processing temperatures are found to be beneficial for obtaining, after squeeze casting a low-porosity material with a large amount of uniformly distributed reaction compounds. However, the preform thickness that can be properly infiltrated is limited to about 6 mm. The homogenisation of the intermetallic phase is complete after only 5 h at 1000 °C. A major problem to be solved is the heterogeneity of the porosity distribution in the sample after homogenisation. This heterogeneity results from an insufficiently uniform distribution of the fibre volume fraction.