Joining of carbon fibre-reinforced silicon nitride composites with 72Ag-26Cu-2Ti filler metal

Abstract

Unidirectionally reinforced carbon fibre/Si₃N₄ matrix composites were joined with 72Ag-26Cu-2Ti filler metal. Joining interfaces were observed by SEM and analysed by energy dispersive spectroscopy. The strength of the joints was evaluated by four-point bending tests. Most of the interfaces of Si₄N₄ matrix/filler metal were firm without cracking and separation. At the interfaces, reaction between the composites and filler metal was limited. Only a concentration of titanium at Si₃N₄ matrix/filler metal interface was confirmed. On the fracture surfaces, many holes left as traces of pull-out of carbon fibres and pulled out fibres could be observed. The maximum joining strength and the average strength, measured by the bending test, were 159 MPa and 107 MPa, respectively. The pull-out process of fibres from the matrix and the reasons for the large scatter in the strength of joints, were discussed. The fibre pull-out behaviour could be related to fibre distribution density at the joining interface.