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

More than 50 powder mixtures with different compositions in the AlCSiTi quaternary system were cold-pressed, heated for 400 h at 1000°C under 105Pa 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 AlCSiTi 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 AlCSiTi 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 AlSi base liquids and each of the solid phases Ti5Si3Cx, Ti3SiC2 and TiC. The Si contents of the AlSi 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 Ti5Si3Cx conjugates with all the solid compounds of the system (Al4C3 and SiC excepted) and that the three-dimensional isobaric-isothermal section is separated into two distinct parts by a three-phase equilibrium Ti5Si3CxAl3TiTiC. The discussion also deals with the thermodynamic aspect of the high-temperature chemical interacton between silicon carbide SiC and TiAl alloys.