5. Conclusions
Room temperature tensile yield and ultimate tensile strength,
dynamic Young’s modulus as well as creep behavior of pure Al and
Al–5, 10, 15 and 20 SiCp composites fabricated by P/M processing
and hot rolling, has been evaluated. The major conclusions of this
study are listed as follows.
Flaws such as cracks in SiC particles and at particle–matrix interfaces
have been introduced in the microstructure of the composites
by hot rolling. These flaws appear to increase with volume fraction
of SiC particles, and have been found to affect the room temperature
mechanical properties and high temperature creep behavior
to different extents. Increase in volume fraction of SiC has shown
modest increase in Young’s modulus, yield and ultimate tensile
strengths. Greater difference between experimentally determined
and calculated Young’s modulus with increasing volume fraction
of SiC is suggestive of poor load transfer at particle–matrix
interfaces.
The creep curves obtained from uninterrupted tests at constant
stress and temperature of 21 MPa and 623 K, respectively have
shown distinct primary, secondary and tertiary stages. The steady
state creep rate increases, while the time to rupture decreases with
increasing volume fraction of SiC due to worsening of load transfer
at particle–matrix interfaces. While tensile fracture seems to occur
by growth of voids in the Al matrix, the creep failure appears to be
promoted by particle–matrix decohesion and linkage of interface
cracks. The time to rupture of each material can be predicted using
the Monkman–Grant relationship, provided the steady state creep
rate is known.