Brazing silicon nitride to an iron-based intermetallic using a copper interlayer

The effect of adding a copper interlayer to absorb the residual stresses produced during cooling of a silicon nitride (Si3N4) ceramic brazed to an iron aluminide alloy was demonstrated. Differential scanning calorimetry (DSC) results showed the positive influence of the copper interlayer in diluting the high-titanium content brazing alloy by decreasing the quantity of active brazing alloy (ABA) available for reaction. The reaction layer formation mechanism was investigated by low voltage line scan FESEM and was shown to consist of a growth competition between the TiN and Ti5Si3 layer. An activation energy of 137 kJ/mol for the reaction layer formation was calculated. A Fe/Cu–Ti alloy reaction at the interface between the Cu interlayer and the FA-129 was observed. This reaction zone extended up to 100 μm in thickness. The maximum bending strength obtained was 160 MPa. All fractures occurred at the Cu/Si3N4 interface, suggesting higher strengths for the FA-129/Cu interface.