Thermodynamically as-received powder particles have a solid-vapor surface energy (𝐽. 𝑚 5! ). The energy per unit mass can be stored as excess surface area (𝐽. 𝑘𝑔 51 ). However it is not thermodynamically possible to consume all the excess surface energy during the sintering, therefore the emergence of the other interfaces add energy to the system such as grain boundaries that cause the densification plateau and the higher relative density couldn't be achieved and the energy is consumed to decrease the surface energy of the grains by consuming the high energy stored at the grain boundaries by coarsening the microstructure.