DIFFUSION REACTIONS BETWEEN SILICON OXYNITRIDE AND SILICON NITRIDE DURING HIP-SYNTHESIS

Abstract
Recent advances in production processes for High Performance Ceramics have made it possible to produce fully dense net shape turbocharger and gas turbine rotors made of silicon nitride. These rotors must usually be attached to a metal shaft by some joining technique. Solid state bonding by diffusion reactions is an attractive route to achieve joints that retain strength at high temperature. Intimate physical contact across the joint during bonding is important for the diffusion process. Hot Isostatic Pressing (HIP) can enhance the contact and thus produce a stronger joint at a lower bonding temperature than other methods. Silicon oxynitride syntesized from a stoichiometric mixture of silicon nitride and silicon oxide by HIP has some interesting properties that might be useful as an intermediate layer in bonding silicon nitride to metals. This work is a part of an assessment to develop solid state bonding methods for the joining of silicon nitride to superalloys by HIP. It presents the first steps in the development, namely the optimization of the synthesis of pure silicon oxynitride during densification by HIP and joining of the oxynitride to silicon nitride during synthesis and densification by HIP. The achievements in these areas and the direction of future work will be discussed.