Ceramics at TWI

Diffusion bonding of ceramics

Relationship between processing parameters for diffusion bonding

Diffusion bonding is a solid state process relying on atomic migration across an interface. The bond is formed during the application of temperature and pressure over a period of time. The two surfaces to be joined require a good surface finish (Ra <0.4µm) and must be clean. As a general rule, diffusion bonding is undertaken at a temperature of 80% of the melting point of the material. If dissimilar materials are used then 80% of the lowest melting point material is used.

The technique can be applied to a wide range of materials including metals, ceramics and combinations thereof.

In many instances direct bonding is not possible due to thermal expansion mismatch or metallurgical incompatibility. It is then that an interlayer or combination of interlayers is used. An interlayer thickness of a few microns is commonly used and this can be pre-placed as a thin foil interlayer or by sputter coating.

In addition, TWI can offer the following facilities:

Joint design
Interlayer design
Materials selection
Sputter coating
Process selection
Joint analysis by Scanning electron microscopy (SEM), optical microscopy Energy dispersive X-ray (EDX), mechanical testing and non-destructive testing (NDT)
Pre-surface assessment can also be made using surface measurement equipment.

Further Information

Best practice guides: Joining ceramics - a guide to best practice
Knowledge Summaries: Diffusion Bonding; Diffusion bonding - ceramics and ceramic/metal joints
FAQs: How do you diffusion bond ceramic to ceramic; Can you diffusion bond ceramics using microwaves
Staff papers: Aluminium metal matrix composites - successes using diffusion bonding Industrial Members Only; Improved facility for high temperature diffusion bonding; Diffusion bonding of titanium alloys; Techniques for bonding ceramics (Bulletin, September/October 1990) Industrial Members Only