Phases and phase equilibria in the quaternary system Ti-Cu-Al-N at 850 °C

Phase equilibria in the quaternary system Ti-Cu-Al-N are investigated using XRD, metallography and EDX, yielding the observation of 18 four phase spaces of the 850 °C isotherm. In the ternary boundary systems Ti-Cu-Al and Ti-Al-N, all previously reported phases are confirmed, but several tielines are newly determined. In the system Ti - N, the new ternary phase Ti 3 CuN dominates most phase fields. Based on thermochemical data of the binary boundary systems and the newly investigated or reinvestigated phase equilibria of the ternary boundary systems, a set of Gibbs energies for the solid phases occuring in the quaternary system is derived, which is used in combination with the quaternary experimental data to derive a large section of the isotherm for Ti-Cu-Al-N at 850 °C. The quaternary η-phase (Ti, Cu, Al) 6 N having the composition Ti 3 Cu 2 Al 1 N 0.8 is found to be the only stable quaternary phase of this system. Several η-phases isotypic to Ti 3 Cu 2 Al 1 N 0.8 are synthesized to explore the crystal chemistry effects of substitutions on different crystallographic sites.