Active Metal Brazing of Machinable Aluminum Nitride-Based Ceramic to Stainless Steel

Shapal (TM)-M machinable AlN-based ceramic and AISI 304 stainless steel were joined by active metal brazing, at 750, 800, and 850 A degrees C, with a dwell stage of 10 min at the processing temperature, using a 59Ag-27.25Cu-12.5In-1.25Ti (wt.%) filler foil. The influences of temperature on the microstructural features of brazed interfaces and on the shear strength of joints were assessed. The interfacial microstructures were analyzed by scanning electron microscopy (SEM), and the composition of the phases detected at the interfaces was evaluated by energy dispersive X-ray spectroscopy (EDS). The fracture surfaces of joints were analyzed by SEM, EDS, and GIXRD (Grazing Incidence X-Ray Diffraction). Reaction between the liquid braze and both base materials led to the formation of a Ti-rich layer, adjacent to each base material. Between the Ti-rich layers, the interfaces consist of a (Ag) solid-solution matrix, where coarse (Cu) particles and either Cu-In or Cu-In-Ti and Cu-Ti intermetallics phases are dispersed. The stronger joints, with shear strength of 220 +/- A 32 MPa, were produced after brazing at 800 A degrees C. Fracture of joints occurred preferentially not only through the ceramic sample but also across the adjoining TiN layer, independent of the brazing temperature.