Basic Principles in Physical Metallurgy - II

The structure and stability of metallic materials needs to be understood before dealing them for a particular service. The materials depends on chemistry and processing condition. Various structures evolves during processing. Therefore one has to understand the distinction among the structures from crystallographic point to view.Here, we have presented a brief account relevant to the structural
aspect. This will help in understanding and identification of the phases by metallographic techniques. The road maps for phase stability, which may be called as phase diagram have been discussed. From phase diagram, we can extract the information about the relative amounts of the various phases, which can be verified and confirmed from micro-structures of the materials. The various invariant liquid state and solid state reactions have been introduced. A few examples of nonequilibrium structures such as nano-crystal, glass and quasicrystal etc.arising due to non-equilibrium processing has been highlighted. A brief
mention has been made about diffusion, precipitation, order-disorder reaction and spinodal decomposition.