Phase-field Study of Plateau-Rayleigh Instability in Multilayer Nanocrystalline Thin Film

Multilayer thin film coatings are actively being developed for numerous applications nowadays. The unique advantage of this type of coating is that it is possible to achieve desirable properties in a single coating by combining different composition with different mechanical properties. It shows higher hardness as well as higher fracture resistance and better tribological properties compared to monolayer coatings of each constituent. Thermal stability of multilayer thin film coatings is of paramount importance for different applications especially tribological applications.

During such tribological applications, temperature in the coated work piece can rise to a very high temperature of around 1000oC from friction between the tool and work piece and lack of lubrication, which is preferred nowadays due to environmental considerations. Hence, for efficient working of hard coatings, optimum mechanical and tribological properties must be maintained at high temperatures. Stability of the multi layers is, therefore, imperative.

I have studied the stability of nanocrystalline multilayer thin film using phasefield simulations that explore systematically the effect of film thickness and grain boundary mobilities. The length scale of this instability problem is in mesoscale and therefore is ideally suited for phase-field model. I have shown by the means of our phase-field model that layer instability in polycrystalline film originates from the grain boundary grooving followed by Plateau-Rayleigh instability. Phase-field simulations yield similar microstructure observed experimentally in our Zr/ZrN multilayer system. From our understanding of the mechanism of the film instability, I have predicted measures which can lead to better stability of multilayer nanocrystalline thin film. Such understanding will help in improving the performance of nanocrystalline multilayer thin film in real life high temperature applications.