In Situ Combustion Synthesis of Ti-Al Intermetallic Compounds in Al Alloy Casting Process

Abstract

Ti-Al intermetallic compounds are regarded as promising materials for the hightemperature structural and coating applications. We focused on the joining of Al casting alloy with Ti-Al intermetallic compounds by in-situ combustion synthesis to improve the surface properties of Al casting components. Microstructures and phase formation behavior of Ti-Al based intermetallic compounds synthesized by combustion reaction were analyzed using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectroscopy (EDS) and x-ray diffractometer(XRD) in Ti-Al intermetallic compounds. Three kinds of titanium aluminides of Ti3Al, TiAl and TiAl3 were synthesized by the heat from the Al molten metal and a coating layer of intermetallic phase were formed simultaneously on solidifed Al alloy surface. The shapes and microstructures of reacted compacts were varied by mixing ratio of elemental powders. The TiAl3 intermetallic compound was observed in the compacts regardless of the mixing ratio of elemental powders. And the unreacted Ti powders were remained in the reacted compacts due to the big size of Ti powder and low exothermic heat of reaction between Ti and Al powders. The zone that poured Al alloy diffused into the reacted Ti-25at.%Al compact of about 200 μm thickness was formed at the interface by the reaction between liquid molten Al alloy and solid Ti powders in green compact.