MICROSTRUCTURE OF DIFFUSIONAL ZIRCONIA-TITANIUM AND ZIRCONIA-(TI-6 WT-PERCENT AL-4 WT-PERCENT V) ALLOY JOINTS

Zirconia-titanium and zirconia-titanium alloy joints were made by diff usion bonding under an inert atmosphere at temperatures in the 1162-14 94 degrees C range. To inhibit the strong oxygen uptake by the titaniu m member a platinum insert was alternatively used. The microstructures and elemental profiles across the joints were investigated by scannin g electron microscopy imaging and energy-dispersive spectroscopy or wa velength-dispersive spectroscopy microanalysis. It was found that dire ct ZrO2-Ti joining produces oxygen saturation in the Ti member and the formation of (Ti,Zr)(2)O at the interface. ZrO2/Pt/Ti joints present a complex layer sequence which at lower temperatures can be described on the basis of the Pt-Ti binary, except near the ceramic where a (Pt, Zr)-rich layer forms; at higher temperatures these joints develop an oxide layer of composition Ti2O3, this oxide probably resulting from l ocal decomposition of the ceramic and reaction of oxygen with the inco ming titanium. When Ti is replaced by the Ti-6 wt% Al-4 wt% V alloy in joints where Pt is present, the main consequences are the presence of liquid at lower joining temperatures and the earlier development of t he oxide layer, now of nominal composition TiO. In all Pt-containing j oints a phase of nominal composition Ti3Pt2 forms; it is advanced that this may be an equilibrium phase not predicted by the Pt-Ti diagrams available. All joints are weak, the fracture path running through the metal in the case of direct ZrO2-Ti joints and through the interface b etween the ceramic and the (Pt,Zr)-rich layer in joints where Pt is pr esent.