Joining of zirconium boride based refractory ceramics to Ti6Al4V

The exploitation of the peculiar characteristics of ceramic refractory materials in extreme conditions (as for Thermal Protection Systems - TPS) often depends to a great extent on the ability to join different ceramics one to the other and to special metallic alloys. Joints may be achieved in a number of ways, but principally are made by either solid phase or liquid phase transformations (brazing). Brazed joints are difficult to realise in the presence of ceramic materials, due to the fact that they are not wet, in general, by liquid metals. This paper presents experimental results on the wettability characteristics of zirconium boride based materials (with Si₃N₄, Ni etc.) by an AgZr alloy, the microstructures and thermal tests of brazed joints with the special alloy Ti6Al4V. The wetting data will be examined in terms of interfacial characteristics and in terms of the kinetics of spreading. Thermal tests and models will be devoted to evaluate and measure the thermal insulation capacity of the ceramic layers in order to determine the optimal thickness as a function of the foreseen outer surface temperature.