Surface precipitation on engineering alloys

The nucleation and growth of solid state precipitates is used extensively
to tailor the bulk mechanical properties of many engineering alloys. It is
less well appreciated that precipitation can also be induced to occur on
the surfaces of engineering alloys using simple heat treatments raising
the possibility of using precipitation as a form of surface treatment.
Surface precipitation occurs through a nucleation and growth process
with kinetics that suggest mass transfer by surface (or interface)
diffusion plays the dominant role. In this presentation, surface
precipitation in a number of Al based alloys is presented, the physical
principles underlying the phenomena are discussed and some
interesting possibilities for ‘surface physical metallurgy’ are highlighted.
Questions of the competition in phase formation on the surface, the
compositions inherited by the growing surface precipitates and the
coupling of bulk and surface diffusion are discussed.