Directed melt oxidation and nitridation of aluminium alloys: A comparison

Directed melt oxidation and nitridation are recently developed in-situ methods for the formation of metal-ceramic composites. Both processes are based on liquid-gas reaction, wherein a molten alloy is reacted with a gaseous species, i.e. oxygen or nitrogen, to form Al2O3/Al or AIN/Al composite microstructures. Composite formation is controlled by the alloy composition, partial pressure of gaseous species, processing temperature and time. Although there are similarities between these two processes, there are differences in the microstructural development. Further, the growth rates of these composites are accelerated using filler materials which provide sites for secondary nucleation and in turn compete with the primary growth of the ceramic phase. The mechanical properties of Al2O3/Al and AIN/Al are comparable, but AIN/Al exhibits higher thermal conductivity and sensitivity to moisture. Finally, the applications and limitations of these composites are presented.