An Integrated Experimental and Numerical Study on the Thin Film Delamination from Micro- to Macro-scale

One of the main problems involved in depositing superhard nanocomposite thin films under a low sputtering-gas pressure is the large compressive stress created in sputtered thin films due to the energetic ion bombardment. To release its compression, the film tends to peel off the substrate, due to the interaction between the geometric instability (buckling) and material instability (decohesion) at the interfacial region. Up-to date, there is still a lack of understanding on the thin film delamination process. Especially, it is not clear how to describe the failure evolution from micro- to macro-scales in general. With an integrated experimental and numerical effort via international collaboration, this proposed project aims to investigate the interaction between the geometric and material instabilities associated with the formation of superhard nanocomposite films (nc-TiN/a-Si3N4; “nc-“ and “a-“ represent “nanocrystalline” and “amorphous” phases, respectively) on engineering substrates (steel, cemented carbide, etc.) fabricated by close-field unbalanced magnetron sputtering. Based on our recent nano-scale observation on the formation of localized deformation before delamination, a systematic experimental study will be performed to explore the transition among failure modes of different degrees of discontinuities and corresponding orientations involved in the buckling and decohesion of compressed thin films. To model and simulate the delamination process from micro- to macro-scale, the Material Point Method (MPM) will be improved with a nonlocal mapping function so that a multiscale constitutive model could be formulated and corresponding bifurcation analysis could be performed. The proposed model-based simulation tool will be verified and improved with experimental data and other solutions available. As a result, a better understanding could be achieved on the failure mechanisms of thin film delamination from micro- to macro-scales.