Microstructural Features of TiAl₃ Base Compounds Formed by Reaction Synthesis

Abstract

Microstructural evolution in TiAl₃ and TiAl₃ base alloys formed by the reaction synthesis between liquid Al and solid Ti or Ti alloys has been studied by carrying out the tests on reaction couples isothermally reacted between 973 and 1373 K for different time intervals. It has been found that the reaction product forms by the exothermic chemical reaction and while TiAl₃ is the only reaction product formed up to the reaction tempperature of 1273 K, TiAl₃ as well as Ti₉Al₂₃ form when the reaction is carried out at 1373 K. In all cases the microstructure of the reaction layer comprises titanium aluminide particles dispersed in an Al rich matrix. However, morphological features of titanium aluminide particles been shown to be widely differing with the reaction conditions. In pure Ti-Al reaction couples an increase in the reaction temperature from 973 to 1173 K leads to the formation of particles having a bi-modal distribution. At the reaction temperature of 1173 K a large number of particles formed contain several micro-cracks. In contrast to TiAl₃ formed in the case of pure Ti-Al couples, the morphology of the TiAl₃ based compounds containing V or Mo, Zr and Si has been found to be significantly different. Instead of being equiaxed, the particles of TiAl₃ based compounds have a continuously changing morphology across the reaction layer. The particles away from the reaction interface, in general, are not equiaxed, and have sharp edges and many of them have severe internal micro-cracks.