Experimental study of ordering kinetics in aluminum alloys during solidification

The microscopic structure and crystallization behavior of liquid Al and Al–0.3Ti–0.02B (wt.%) are studied by timeresolved neutron diffraction measurements during the liquid–solid phase transformation for continuous cooling. A specially developed furnace insert was used to obtain a temperature stability of 40 mK in the vicinity of the solidification temperature of To = 933 K. The evolution of the static structure factor S(Q) has been monitored during the liquid to solid phase transformation as a function of the cooling rate. The evolution of the liquid fraction fL during the transformation is determined from the value of the first peak in the liquid structure factor. The evolution of the solid volume fraction fS = 1fL is analyzed in terms of the Johnson–Mehl–Avrami model. The Avrami exponent n is found to change for pure Al as well as for Al–0.3Ti–0.02B alloy with cooling rate and the rate constant k decreases by an order of magnitude for Al–0.3Ti–0.02B alloy compared to pure Al. Anomalous temporal oscillations were observed in the Bragg peak intensity of the solid grains during the solidification of the Al–0.3Ti–0.02B alloy.  2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.