Cr. Ho et B. Cantor, HETEROGENEOUS NUCLEATION OF SOLIDIFICATION OF SI IN AL-SI, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 173(1-2), 1993, pp. 37-40
The heterogeneous nucleation of the solidification of Si by Al has bee
n studied in melt-spun Al-3wt.%Si alloys, using a combination of diffe
rential scanning calorimetry (DSC) and transmission electron microscop
y (TEM). Melt-spun alloy samples have been heated in the DSC apparatus
to above the Al-Si eutectic temperature of 577 degrees C, followed by
cooling, to monitor the solidification exotherms of Si-rich liquid dr
oplets embedded in a solid Al matrix. The kinetics of the heterogeneou
s nucleation of the solidification of Si by the surrounding matrix are
difficult to analyse, because of compositional variations during cool
ing. Alloys made with 99.9999% pure Al have a microstructure of eutect
ic droplets which contain a fine cluster of Si particles embedded in a
n Al matrix. The eutectic droplets nucleate at about 517 degrees C, ie
. 60 K below the eutectic temperature. The effect of the cooling rate
on the shape of the solidification exotherms has been analysed to give
a contact angle of 43 degrees at the Al-Si-liquid triple point.