The self-assembly mechanism of alternating AlN/TiN nano-lamellar structures in AlTiN coating is still a mystery, though this coating has been widely used in industry. Here, by using the phase-field crystal method, we studied the atomic-scale mechanisms of the formation of nano-lamellar structures during spinodal decomposition transformation of an AlTiN coating. The results show that the formation of a lamella is characterized by four distinct stages including the generation of dislocations (stage I), formation of islands (stage II), merging of islands (stage III), and flattening of lamellae (stage IV). The locally periodic fluctuation of the concentration along the lamella leads to the generation of periodically distributed misfit dislocations and then AlN/TiN islands, while the fluctuation of the composition in the direction normal to the lamella is responsible for the merging of islands and flattening of a lamella and more importantly the cooperative growth between neighboring lamellae. Moreover, we found that misfit dislocations play a crucial role in all the four stages, promoting the cooperative growth of TiN and AlN lamellae. Our results demonstrate that the TiN and AlN lamellae could be produced through the cooperative growth of AlN/TiN lamellae in spinodal decomposition of the AlTiN phase.
Keywords: AlTiN coating; nano-lamella; phase transformation; phase-field simulation; spinodal decomposition.