Friction welding can often involve joining one material directly to a dissimilar material. In third-body friction joining, an additional material (the third body) is used to join the two dissimilar materials together (see illustration).
In the simplest form of the process, granules of the third-body material are placed in a drilled hole in one of the materials to be joined. The other material, in the form of a cylindrical stud with re-entrant features on its diameter, is rotated and pushed into the hole, creating frictional heat. Re-entrant features should also be present on the diameter of the hole.
The third-body material, which has a lower melting point than the two main materials being joined, plasticises and flows around the stud and into the re-entrant regions. On cooling, the third-body consolidates and locks the materials to form a secure joint.
Depending on material compatibility, the third-body may metallurgically bond to either or both materials. It may not bond to either, but the joint will still be secure. Joints can usually be produced without deforming the components.
Feasible joint combinations include ceramic/ceramic and metal/ceramic. The process is also suitable for powder metallurgy manufactured materials. Relevant thermal expansion characteristics of the materials being joined and the third body filler should be considered, as the third body should be in compression at its service temperature.
Alternatively, third-body materials can be clean machined swarf or a solid plug. Also, the third-body could be a braze metal; frictional heat causes this to melt and flow into the gap between the materials being joined.
For further information please see Joining Technologies or contact us.