Abstract
Formation of ceramic particles in intermetallic Ti-46Al-2W-0.5Si (at.%) alloy directionally solidified in alumina moulds was studied. The ceramic particles formed due to a reaction between the melt and the mould were identified to belong to α-Al₂O₃ phase. The reaction was found to occur preferentially at the mould grain boundaries. The diffusion controlled attack of grain boundaries resulted in a release of grains from the mould. Moving solid-liquid interface assured homogenous redistribution of the particles from the reaction zone into the whole volume of directionally solidified ingots. Increasing reaction temperature and time increased volume fraction and size of the particles. The volume fraction of particles was found to follow V_c ~ t_r^m law with the time exponent of m = 0.62, and the activation energy for particle formation was determined to be Q = 375 kJ.mol^-1.

Key words
intermetallics, titanium aluminides, crystal growth, kinetics, composites

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