Interfacial microstructure and high-temperature strength in silicon nitride/nickel-based superalloy bonding

Reliable Si3N4/nickel-based superalloy joints were obtained by partial transient liquid phase bonding with a Ni/Cu/Ti multi-interlayer. The flexural strengths of the joints were investigated at elevated temperatures. The maximum high-temperature bending strength of 115 MPa was achieved when the joint was tested at 1073 K. Microstructures and compositions of the joints after high-temperature testing were analyzed by scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy (TEM). A reaction layer with a thickness of about 3 μm was developed at the interface. The TEM results revealed a fine grain microstructure in the reaction layer of the joint after undergoing bending test at 1073 K. Cu-rich precipitates are observed in the fine-grained reaction layer by TEM. In addition, the high-temperature fracture mechanism of the joints was discussed. The fractures of the joints at room temperature exhibited a brittle fracture characteristic, while plastic deformation of the interlayers in the joint occurred at elevated temperatures.