Phase equilibria at 1000°C in the AlCSiTi quaternary system: An experimental approach

Abstract More than 50 powder mixtures with different compositions in the Al C Si Ti quaternary system were cold-pressed, heated for 400 h at 1000°C under 10 5 Pa argon (1 atm) and rapidly cooled. Phases present in the as-treated samples were characterized by X-ray diffraction, optical metallography, scanning electron microscopy and electron probe microanalysis. From the results obtained, a three-dimensional isobaric-isothermal section of the Al C Si Ti phase diagram has been constructed, using the classical equilateral tetrahedron representation. Different two-dimensional sections through this tetrahedron and projections on its faces have also been drawn. These constructions are discussed with the aim to provide a comprehensive description of the phase equilibria that tend to be established in the Al C Si Ti quarternary system at 1000°C under a pressureof 1 atm. Among the most important results, one can mention the existence of liquid-solid phase equilibria between Al Si base liquids and each of the solid phases Ti 5 Si 3 C x , Ti 3 SiC 2 and TiC. The Si contents of the Al Si base conjugate liquids are, respectively, within the limits 8–10.5 at.%, 1–19 at.% and 0–11.5 at.%. Moreover, it is worth noting that Ti 5 Si 3 C x conjugates with all the solid compounds of the system (Al 4 C 3 and SiC excepted) and that the three-dimensional isobaric-isothermal section is separated into two distinct parts by a three-phase equilibrium Ti 5 Si 3 C x Al 3 Ti TiC. The discussion also deals with the thermodynamic aspect of the high-temperature chemical interacton between silicon carbide SiC and Ti Al alloys.