Fig. 4 represents TEM nanostructure images of AR-SiC (Fig. 4(a)
and (b)) and preform samples (Fig. 4(c–f)) after semi-solid stir casting.
Fig. 4(b), (d) and (f) are schematic illustrations corresponding
to the nanostructures seen in Fig. 4(a), (c) and (e), respectively. As
shown in Fig. 4(a), nano SiC particles in the AR-SiC sample have a
high tendency to agglomerate during stir casting in order to reduce
their free surface energy. As can be seen in Fig. 4(a), the vast majority
of SiC particles in the AR-SiC sample have a high propensity to
agglomerate at grain boundaries instead of within the grain interior,
and this is attributed to the effect of the particle pushing
mechanism during solidification, as shown by arrows in Fig. 4(b).
However, as can be seen in Fig. 4(c), in the case of preform samples,
the majority of well-dispersed SiC particles reside in the grain interior
rather than at the grain boundaries, and this is ascribed to the
effect of the particle engulfment mechanism during solidification,
as demonstrated by arrows in Fig. 4(d).
In fact, the better distribution of SiC particles