The influence of oxygen impurities on the formation of AlN–Al composites by infiltration of molten Al–Mg

The influence of residual oxygen in nitrogen on the formation of AlN–Al matrix by reactive infiltration has been investigated. Increasing the oxygen content from 10 ppm upwards decreased the nitride content in the matrix from 64 to 6%. Based on the analysis of the availability of oxygen at the Al-melt/gas interface, three distinct scenarios have been proposed: (i) at lowest values, oxygen does not interfere with either infiltration or nitridation reaction; (ii) at intermediate values, nitridation is suppressed, however infiltration continues; and (iii) at a critical upper value, the melt passivates without any infiltration. This phenomenon offers control of the AlN/Al ratio in the matrix and the possibility of creation of microstructural gradients by the appropriate choice of gas mixtures.