Fig. 5 shows SEM micrographs of microwave and SPS sinter
samples and reveals the uniform distribution of reinforcements
aluminum matrix in both sintering methods. In the microwa
sintered sample (Fig. 5a) some porosity exists in themicrostructur
but for the SPS sintered sample (Fig. 5b) no porosity is observed.
seems that in themicrowave sintering the formation of Al3BC at t
interface of aluminum and B4C particles is accompanied by t
formation of porosity around some B4C particles. The formation
porosities in this condition may be attributed to the mismatch
thermal expansion coefficients of aluminum, Al3BC and B4C par
cles and also the different crystal structures. However, the mic
cracks and porosity around the different particles were n
observed in the SPS process may be due to the simultaneo
application of pressure and higher sintering time. These conditio
could compensate and prevent the creation of micro cracks an
porosity arising from the mismatch of thermal expansion c
efficients and crystal structures of aluminum, Al3BC and B4C pa
ticles [29].