Interfacial reaction mechanisms in Syalon ceramic bonding

Abstract

The increasing application of Si 3N 4 and related ceramics as engineering materials demands larger and more complex shapes. One solution to the fabrication problem of monolithic components lies in the effective joining of smaller shapes. Active metal brazing of a Syalon (SiAlON) ceramic was investigated using a series of binary brazing alloys. Titanium, chromium and zirconium additives are chosen since they are good nitride formers. Brazing is performed under a moderate applied pressure (7–11 kN m −2) under vacuum (10 −4 Torr), a temperature between 800 and 1100°C and a time of 1–20 h. Cohesion depends on the occurrence of a reaction between the active metal and the ceramic to form a continuous nitride layer at temperature. The bond strengths are measured in four-point bend testing and the highest values attained approach 400 MPa. Typical levels for the ceramic lie between 500 and 1000 MPa. Bonds are examined using scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction to determine the interface structure and the identify of phases present.