Are you trying to design a quiet gun or make a wind chime or quiet your neighbor's wind chime?
I do not understand "has used different materials of metal knowing their harmonics to cancel or deaden the vibrations". Do you mean natural frequencies instead of harmonics?
There are some metals with enhanced damping properties, and perhaps these search links would help:
Search: vibration damping properties of metals
Strong, yes frequency would probably be a better description.
I was curious if the use of a softer material such as Copper laid over steel would reduce effects of vibration similar to a copper head on a steel hammer used in metal working does.
I still do not understand what you are looking for! Soft metal on hammer is typically to reduce surface damage and reduce multiple impacts and bounce-back.
There is a technique for damping a metal panel, simply spotweld a second panel to it, of a substantially different thickness. In general mismatched layers do add damping, but I suspect for feasible thicknesses of tubes they'd just act like the weighted average of the two materials. however
