Control of Interfacial Reactivity Between ZrB2 and Ni-Based Brazing Alloys

Transition metals diborides (Ti,Zr,Hf)B2 play a key role in applications where stability to extremely high temperatures and damage tolerance are required, but they still pose problems of production and joining with themselves and to the underlying supporting structure. In this work the reactivity at the solid-liquid interface between ZrB2 ceramics and Ni-based brazing alloys will be addressed; it will be shown how the reactivity and the dissolution of the solid phase can be controlled and even suppressed by adjusting the brazing alloy composition on the basis of thermodynamic calculations. Wetting experiments of ZrB2 ceramics by Ni, Ni/B 17 at. % and Ni/B 50 at. % were performed at 1500 and 1200°C by the sessile drop technique. The obtained interfaces were characterized by optical microscopy and SEM-EDS; the Ni-B-Zr ternary diagram was assessed by the CALPHAD method. A correlation between microstructures, shape of the drops, spreading kinetics, substrate dissolution and the phase diagram was found. The effect on the interfacial reactivity of Si3Ni4 used as sintering aid and issues related to Si diffusion into the brazing alloy is discussed as well.