Basic mechanisms and interface reactions in HIP diffusion bonding

The influence of interface reactions on the basic mechanisms of HIP diffusion bonding is addressed in this paper. It is shown that the mechanisms that control the microstructure and properties of solid state diffusion bonds are strongly influenced by the pre-bonding processing route used in their manufacture and by the precise chemistry of the materials being joined. In the case of precipitation hardened martensitic stainless steels the interface may be contaminated by oxide particles, which form during the early stages of the bonding process, and whose composition and morphology depend upon the chemistry of the steel. Such particles prevent grain growth across the interface and result in tensile fracture at the interface. Refinements to the pre-bonding processing route have resulted in significantly lower particle densities and grain growth across the interface. Detailed studies have revealed that under certain circumstances, HIP diffusion bonds may also be weakened by precipitation reactions or sulphur segregation at the interface during processing.