Oscillating local minimum energy site and its effect on the spinodal decomposition of TiAlN: A first-principles study

Abstract

Experimentally it observed that when TiAlN undergoes spinodal decomposition, AlN may nucleate either at grain interior, at grain boundary, or even in layer interior to form nanolamellar when within multilayer structure. To unveil the atom-scale mechanism of the spinodal decomposition at the initial stage, in this work, the structures, total energies, and electronic structures of TiN(100)/Ti1-xAlxN(100) multilayer with Al doping in different sites were investigated systematically by the first-principles calculations. The results of total energy show that the local minimum energy sites are oscillating, which makes it possible for the nucleation and precipitation of c-AlN at the interface and inside the Ti1-xAlxN (x = 0.25, 0.5) layer in TiN(100)/Ti1-xAlxN(100) multilayer, agreeing with the experimental observations. Moreover, spinodal decomposition of TiAlN multilayer to form alternating stacks of c-AlN and TiN nanolamellars, which has been experimentally observed in the (Ti,Al)N/TiN multilayer, can be explained by the oscillating behavior of the local minimum energy site. And the electronic structures of TiN(100)/Ti1-xAlxN(100) multilayer with Al addition reveal that the low-energy doping site is probably related to the strong interaction between Al-doped and neighboring N atoms to reach a more stable state.