| The Ceramic-Matrix-Composites (CMCs) have come into
prominence for structural applications because of their
superior mechanical properties both at room temperature
and at elevated temperatures. In conventional processing
route of pressureless sintering, the rigid reinforcement
phase (particulate or whisker) severly retards the densification.
The obvious solution of high temperature hot pressing
or HIPing makes the process energy and cost intensive.
Some recent developments on the reaction-forming of
CMCs such as self propagating high temperature synthesis.
(SHS), co-continuous ceramic composites (C4 materials),
directed metal oxidation (DIMOX) etc have, however,
opened up new areas of applications for CMCs like wear
resistant parts for a variety of process industry equipment,
automobile and armour components.
The present paper describes the in situ processing of
alumina based CMCs by directed oxidation of aluminium.
This process essentially in •·olves a rapid oxidation of a
molten At-alloy with the vapour phase oxidants and an outward
growth of the ceramic phase. Moreover, its novel feature
is its ability to form near·-net shaped components. This
is possible by growing the ceramic/metal product phase into
the void space of a reinforcement preform made out of particulate,
whisker, continuous fibre etc. The structure and
properties of the resultant composite material can be controlled
by varying the relevant growth parameters, viz. temperature,
alloy chemistry, atmosphere and the filler phase
geometry. The microstructural evolution and the infiltration
kinetics of the composites have been exemplified in the context
of oxidative interaction of 11 binary Al-Mg alloy with the
SiC and fused alumina preform components. |
