Diffusion bonding is typically utilized for ferrous parts which are fairly small in size. Hence, part geometry can be a concern. To avoid this complication, sintering and diffusion bonding can potentially be carried out in the same furnace. Diffusion bonding is often employed to provide a transient liquid phase for bonding at the interface. The presence of resulting reaction products such as oxide compounds may reduce the bond strength.
To induce high bond strength diffusion can be activated via the addition of suitable elements, such as Cu in, for example, ferrous PM parts. When compared with other joining techniques, rather low strength joints can be expected from diffusion bonding, which may be limited to certain geometries and Diffusion bonding has been a choice when handling more exotic compositions where the chemistry of the part plays a significant role in the joining process and its feasibility. Hence, applications have been focused on light materials such as Ti alloys, MMCs and special products. More conventional C–Mn steels have not been commonly diffusion bonded.
Although an attractive option, the success of the bond strength gained by this joining technique critically depends on compositions and hence phase transformations and may require protective atmospheres (inert such as argon, or reducing, such as hydrogen) which bring additional considerations such as complexity and cost of production.
Small volume high performance and added value components may therefore be more favorable for diffusion bonding and the technique may well be the only option for joining such materials. Similar to brazing, diffusion bonding has also found applications in HIP components.
Information Reference: https://www.sciencedirect.com/topics/engineering/diffusion-bonding