THE FINE-SCALE MICROSTRUCTURE OF RAPIDLY-QUENCHED ALUMINIUM-TRANSITION METAL ALLOYS

Rapid-solidification processing of metallic alloys can achieve refined grain structures, increased chemical homogeneity, extended solid solubility and metastable phase formation. The production and properties of material produced by one such technique, that of evaporation-condensation, are described, whereby bulk quantities of aluminium alloys containing substantial percentages of transition metals in solid solution can be produced. The current situation in the microstructural characterisation of these types of alloys, typified by Al-Cr-Fc. is then summarised using evidence from X-ray and neutron diffraction, analytical electron microscopy, small-angle neutron scattering and atom-probe techniques. The as-deposited microstructure is characterised by a super-saturated solid solution with a distinctive columnar grain structure and some evidence of solute clustering. Artificially-aged microstructures show rejection of excess solute to form a homogeneous distribution of Fe-rich precipitates of Fc3Al, and an inhomogeneous distribution of Cr-rich precipitates which could be identified unambiguously as Al13,Cr2 after about lh ageing at 350°C.