SIMULATION AND MEASUREMENT OF A VERTICAL BRIDGMAN GROWTH SYSTEM FOR BETA-NIAL CRYSTAL

A coordinated theoretical and experimental study of the temperature di stribution inside a customized vertical Bridgman system for growing be ta-NiAl crystal has been conducted. The theoretical model accounts for the combined effects of phase change dynamics, the coupled heal trans fer processes of conduction, convection and radiation, variable materi al properties, and complex geometry pertaining to the system. Comparis ons between numerical predictions and experimental measurements show s atisfactory agreement. The accuracy of the melting temperature of NiAl with stoichiometric composition, along with important processing para meters such as interface curvatures and temperature gradients across t he interface, have been discussed in detail. Also assessed are possibi lities of improving the solidification process, including coating the ampoule outer wall with a material of high radiative emissivity or dec reasing the ampoule wall thickness. (C) 1997 Elsevier Science Ltd. All rights reserved.