Microstructure of diffusional zirconia–titanium and zirconia–(Ti–6 wt% Al–4 wt% V) alloy joints

Zirconia–titanium and zirconia–titanium alloy joints were made by diffusion bonding under an inert atmosphere at temperatures in the 1162–1494°C range. To inhibit the strong oxygen uptake by the titanium member a platinum insert was alternatively used. The microstructures and elemental profiles across the joints were investigated by scanning electron microscopy imaging and energy-dispersive spectroscopy or wavelength-dispersive spectroscopy microanalysis. It was found that direct ZrO2–Ti joining produces oxygen saturation in the Ti member and the formation of (Ti,Zr)2O 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 local decomposition of the ceramic and reaction of oxygen with the incoming 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 the oxide layer, now of nominal composition TiO. In all Pt-containing joints 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 between the ceramic and the (Pt,Zr)-rich layer in joints where Pt is present.