Configurational Force

Why will a microstructure evolve?

     To explain the idea, let us look at a simple example - the shape evolution of a solid particle.  Assume that the particle has initial shape of an ellipsoid.  Over time it will evolve into a sphere.  The following figure demonstrates the process.

    Why?  According to thermodynamics laws, a system prefers a state with lower free energy.  In this example, the Gibbs free energy is surface energy, calculated by the surface energy per unit area g  times the area of the surface A.  The particle has different Gibbs free energy at different shapes.  With volume the same, a shape closer to that of a sphere has smaller surface area and lower Gibbs free energy.  The energy difference constitutes a driving force for the evolution of the particle.  Under this driving force, the atoms diffuse and relocate, which causes the shape change of the particle.  Finally we will obtain a sphere.

The following are the key points we can learn from the example.

• Free energy depends on configuration

• Configuration evolves to reduce the free energy– driving force

• Configuration changes by atomic diffusion