The simple rule of thumb is this: If you can forge it, you can friction-weld it.
We have forged those!
We have not tried forging those, but it doesn't mean we can't
Unique Material Combinations
Materials listed here as ‘compatible’ represent materials that have been successfully joined. If a combination of materials does not appear here, it may only indicate that it has not been tried; not that it is impossible.
Sampling of commonly welded materials by MTI:
Aluminum > Titanium
Carbon Steel > Monel
Steel > Aluminum-bronze
Titanium > Copper
Titanium-aluminide > Inconel