Mechanical integrity analysis of multilayer insulator coatings on flexible steel substrates

• Published in: Thin solid films 2007-06, Vol.515 (17), p.6890-6898
• Main Authors: Plojoux, J., Leterrier, Y., Månson, J.-A.E., Templier, F.
• Format: Article
• Language: English
• Subjects: Adhesion; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Fragmentation; Insulator coating; Mechanical and acoustical properties; Physical properties of thin films, nonelectronic; Physics; Steel substrate; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2007.01.050

The cohesive and adhesive properties, and related critical radius of curvature of thin multilayer insulator coatings on a 152 μm thick flexible steel substrate were investigated using tensile experiments carried out in-situ in an optical microscope. This method was found to be well adapted for the two types of coatings studied: SiO 2 single layers with different thickness and SiO 2/SiN x /polyimide stacks. Special attention was paid to the influence of surface roughness and yielding of the steel substrate. Coating delamination and spallation was observed at low strain in case of SiO 2 coatings on unpolished steel, resulting from roughness-induced stress concentrations and slippage of grain boundaries. Polishing the steel substrate, or using a polyimide interlayer, was found to be useful to avoid premature delamination of the layers. In all investigated cases, a critical radius of curvature for layer damage of approximately 5 mm was found.