INTERFACES OF SIC FIBERS AND AL-5-PERCENT MG DEVELOPED UNDER SYSTEMATICALLY VARIED PROCESSING CONDITIONS

In the present work, attention has been focused on the processing-depe ndent nature of the interface of SiC fibre-reinforced Al matrix compos ites fabricated by pressurized liquid metal infiltration. To determine the effect of variation of the processing parameters on the interface formation, Tyranno continuous SiC fibres have been infiltrated with A l-5% Mg melt under a range of melt superheat and infiltration pressure conditions. During processing the major processing parameters of the pressurized infiltration were precisely monitored. Analytical transmis sion electron microscopy of the obtained interfaces was employed to st udy the nature and extent of the interfacial reactions. Oxygen pre-exi sting in the fibres results in the formation of an interfacial oxide l ayer. The chemical reaction between SiC and Al occurs by Al penetratio n, in situ SiC decomposition and Al4C3 formation. Surplus C and the re duced Si diffuse into the interfacial matrix, resulting in the formati on of interfacial Si and/or Mg2Si and interfacial Al4C3 protruding int o the matrix. Mg in the melt preferentially penetrates into the fibres but does not cause any observable variation in the fibre structure. I ncreases in melt superheat and infiltration pressure intensify the int erfacial reactions. It is also found that the extent of the interfacia l reactions and interfacial binding can be significantly altered by th e geometrical location of the interface in question.