SYNTHESIS, PROPERTIES, AND TERNARY PHASE-STABILITY OF M6X COMPOUNDS IN THE TI-CU-O SYSTEM

A section of the Ti-Cu-O ternary phase diagram was investigated at 925 -degrees-C. The system contains two M6X-type compounds, Ti4Cu2O and Ti 3Cu3O, which are isostructural with the eta-carbides and are stabilize d by O. The presence of two of these compounds and the size of their s ingle-phase fields contradict earlier predictions in the literature ba sed on the valence and location of the elements in the periodic table. It is proposed that the atomic radii of the elements may also be a fa ctor, especially for compounds containing Ti. The two observed M6X-typ e compounds occur as products of reaction at the Ag-Cu-Ti/Al2O3 interf ace. The compounds were synthesized in bulk for characterization of th eir properties which influence the performance of the brazed joints. T he compounds are stable in inert atmospheres up to their melting point s, but are easily oxidized in ambients containing even trace amounts o f O and form a coherent layer of reaction products. The values of elas tic coefficients, thermal expansion, and resistivity of these compound s are intermediate between those of Al2O3 and Cu and would therefore p rovide a gradual transition across the interface.