Importance of interface chemistry in hipping diffusion bonding of precipitation hardened martensitic stainless steels

The effect of processing route on the microstructure and properties of hot isostatically pressed diffusion bonds, manufactured from precipitation hardened martensitic stainless steels, is addressed in this paper. The quality of the diffusion bond was assessed using a range of analytical techniques and a programme of mechanical testing. It is shown that the microstructure and properties of the diffusion bond are strongly influenced by the prebonding processing route used in its manufacture. Using conventional encapsulation techniques the interface is contaminated by oxide particles, whose composition and morphology depends upon the precise chemistry of the steel. These particles prevent grain growth across the interface and frequently result in tensile fracture at the interface. Refinements to the prebonding processing route result in lower particle densities and grain growth across the interface. However, these measures result in the interface becoming weakened by the precipitation of copper at the interface.