The Al/SiC powders produced were hand sieved per ASTM
C-136 using ASTM E-11 sieves (ASTM stands for “American
Society for Testing and Materials”). This process involved placing
the total sample in the initial N300 μm sieve and shaking it for
over 10 min. The contents in the catch pan were then weighed.
The shaking was continued into the cleaned catch pan until the
rate of particle passage into the catch pan was less than 0.1%of the
total feed rate per minute. This process was repeated for every
sieve size down to 38 μm.
After the produced particles were sieved, the volume and
weight fraction of each component of the matrix was obtained.
Ideally particle volume or weight fraction should be determined
experimentally by matrix disintegration methods outlined in
ASTM D3171-76. The materials necessary to use the ASTM
method were not available to the authors so an alternative method
of estimating the particle volume fraction was devised. The Al/
SiCMMC particlesweremounted in an epoxy and polished using
standard metallurgical procedure. Representative particles from
each size range were photographed at magnification of either
400X or 1000X. A grid was laid over each photograph. The area
percentage of each component (SiC, aluminum or void) in each
block of the grid was estimated for the entire surface of the particle.
The total number of squares that composed the particle was
summed. The area fraction was estimated by dividing the number
of squares of each component to the total number of squares.
This is illustrated in Fig. 5. SiC particles appear as solid black
areas in the photographs. The voids were harder to identify. They
appear as unfocused regions in the photographs, often located
next to SiC particles. While the specimens were examined under
the microscope, these regions could easily be identified. This is
because different areas along the side of the void could be brought
into focus giving a sense of depth. If the SiC particles are evenly
distributed throughout the aluminum particle the area fraction is
approximately the same as the volume fraction. The volume
percentage of voids present in the MMC particles could not be
determined from the methods outlined in ASTM D3171-76.