Joining of sialon ceramics by a stainless steel interlayer

In direct diffusion bonding of sialon to stainless steel, thermal residual stresses arise due to the difference in coefficient of thermal expansion of the two materials. These stresses frequently lead to failure of the bond. This behaviour is further influenced by the formation of interfacial reaction layers between ceramic and metal and the problem is essentially one of asymmetry of stresses in the interface between dissimilar materials. The present study demonstrates that a thin layer of austenitic stainless steel can be used as an interlayer to join two sialon components. In such a case the distribution of residual stresses is symmetrical across the composite join and provided that the thickness of the steel layer is less than a critical value, then fracture on cooling from joining temperature does not occur. The development of this process is described and a finite-element model has been used to predict the properties of the interfacial reaction layer between steel and ceramic which are consistent with the experimental observations.