SOLIDIFICATION MICROSTRUCTURE OF LASER REMELTED AL2O3-ZRO2 EUTECTIC

Surface resolidification experiments using a high power CO2-laser have been performed Al2O3-ZrO2 containing 36.8 at.% ZrO2 eutectic alloy at beam velocities between 0.3 and 8 mms The local growth rate has been measured by observation of the orientation of the microstructure using scanning electron microscopy. In the whole range of velocities, the s tructure is essentially a regular lamellar eutectic and the value of t he growth product lambda(2)V was found to be approximate to 9.6 10(-17 ) m(3).s(-1) The measured eutectic spacings were compared with Jackson and Hunt model. Using thermophysical properties from the literature, the measured spacings were more than four times larger than the calcul ated ones. Assuming all parameters of the growth relationships except the diffusion coefficient to be of the right order of magnitude or to have a negligible influence, agreement is found when using a larger li quid diffusion coefficient, D-L approximate to 5.10(-10) m(2).s(-1). ( C) 1997 Acta Metallurgica Inc.