Employing reactive synthesis for metal to ceramic joining for high temperature applications

Joining of dissimilar materials allows the properties of both materials to be exploited in a device or structure. The main reasons for the incorporation of dissimilar materials are to achieve function, improve efficiency and to reduce cost.Silicon nitride is an engineering ceramic that has outstanding properties but has yet to find its full commercial potential. Silicon nitride is suitable for high temperature applications, however, its incorporation into devices or structures tends to be restricted due to a lack of suitable joining techniques.This paper presents the results of joining between the high temperature and corrosion resistant iron-chromium-aluminium alloy (Fecralloy) with silicon nitride by a nickel aluminide (NiAl) interlayer. The formation of NiAl from its constituent elements (Ni-Al compact was used) by reactive synthesis is highly exothermic and this was utilised to cause partial melting of the Fecralloy interface and reactive wetting of the silicon nitride interface.Joints with average shear strength of 94.3 MPa were fabricated under optimum processing conditions (900°C, 15 min, 45 MPa). Thermal cycling at 850°C in air showed that the joints could be used at this temperature.The primary focus of this work was on the effects of process conditions upon the microstructure and mechanical properties of the joint. The reactive synthesis of NiAl was studied using differential thermal analysis (DTA), where the effects of varied heating rate were investigated.