TWI offers a host of diffusion bonding services to our Members. We take pride in offering a full and rounded solution to our Members, and take great care to ensure that we recommend the techniques that best suit your circumstances, paying particular attention to:
- Process selection
- Metallurgy
- Component design
- Testing
Our advice is always impartial because we are not allied to the suppliers of any particular suppliers of equipment or consumables.
TWI's multi-disciplinary team has over 60 years of experience in diffusion bonding types, including vacuum, controlled atmosphere, resistance and induction heating, uniaxial, and transient liquid phase diffusion bonding (diffusion brazing). Materials that we have successfully diffusion bonded include aluminium alloys, titanium alloys, steels (carbon, stainless and ODS), nickel superalloys, Haynes alloys, Fe-Co alloys, zirconium alloys, copper alloys, silicon carbide (SiC), silicon nitride (Si3N4), and metal matrix composites (MMCs).
Diffusion bonding offers numerous benefits to a wide range of industry sectors and applications, particularly where there is a need to join dissimilar materials.
The main advantage of this technique is that, unlike welding, it is not a 'fusion' process, so the parent materials to be joined are not melted. This allows diffusion bonding to join metals and ceramics in both similar and dissimilar combinations.
Other advantages include:
- Re-working
- Near-parent properties
- Minimal shape change to parts
- No post process surface finishing required
What is Diffusion Bonding?
Also known as diffusion welding, diffusion bonding is a solid-state welding method that is performed in a vacuum or inert gas environment. The technique can be used to join both similar and dissimilar materials, typically metals, although ceramic materials can also be joined using this process.
Diffusion bonding uses the principle of solid state diffusion that works through a combination of heat and pressure. By applying pressure to the materials at an elevated temperature, the atoms of two solid surfaces diffuse and combine. When used with similar materials, diffusion bonding is completely autogenous. When welding dissimilar materials, cross-sectional interlayers can be used.
Diffusion Bonding Temperatures
Although it is possible to achieve a weak bond at room temperature, diffusion bonding typically performed with a bonding temperature of around 50-80% of the melting point (Tm) of the materials. However, at TWI, we tend to perform diffusion bonding at around 70-90% of the Tm. While the relatively low temperatures used negate thermal expansion, those materials with higher melting points require higher temperatures to bond.
Bonding Environment and Preparation
Commercial diffusion bonding is typically performed in a vacuum furnace with hydraulic rams that apply pressure to the parts to be joined. This process, known as uniaxial diffusion bonding, requires an applying force to bring the material surfaces into intimate contact. The smoother the surface, the better the bond as there are fewer voids to diminish the materials’ contact and thereby the bond strength.
Those materials that are not compatible with vacuum conditions can be bonded under the partial pressure of an inert gas, such as argon or N2.
In theory, it is possible to join surfaces of any size with diffusion bonding, however, practical limits are set for the process based on the pressure required and the physical limitations of vacuum chamber sizes.
Diffusion Bond Characteristics
Because diffusion bonding can be performed without the need for filler materials, no weight is added to the final parts. The joins created with this process tend to exhibit the same strength and temperature resistance as the base materials.
The relatively low temperatures used mean that the materials endure little or no plastic deformation. Diffusion bonding also introduces very little residual stress and no contamination into the weld.
Benefits
The benefits of diffusion bonding as a process include:
- The bonded surface retains the same mechanical and physical properties as the base materials, with little or no plastic deformation
- Because the bonding process produces high quality joints with no discontinuities or porosity at the interface, the material can be heated, sanded and otherwise manufactured
- Allows for the creation of high precision components with complex shapes
- Capable of joining both similar and dissimilar materials
For more information, please contact us:
contactus@twi.co.uk