Laminated Composite Thin Films: A Solution to Improve Cutting Tools Performance
In cutting applications hard thin films of coated tools are expected to be wear and oxidation resistants, and with strong adhesion to the substrate. Due to the high loads involved in the contacts, the main efforts must be supported by the substrate and it is supposed that the coatings follow their elasto-plastic deformation, with a subsequent delay of the crack propagation. The commercial thin films used for these applications are generally monolithic and homogeneous or heterogenous(chemical compositional gradient up-down). Even the nanostructured coatings will perform under these loads as monolithic coatings, and the crack generation and propagation will be ruled by the same mechanisms as in the monolithic coatings. Hence, the hard coatings for cutting tools must be able to deflect surface cracks and exhibit the highest adhesion to the substrate. In order to achieve these characterisitics, the common Ti-Al-N was selected as hard coating, and thin ductile metal interlayers (few tenths of nanometres) were introduced inside Ti-Al-N thin film as long period multilayer coatings – nanolaminate coatings. The presence of interlayers revealed efficiency in dissipation of the energy generated during the application, decreasing the propagation cracks across the coating and ensuring the best adhesion. The mechanical behavior observed is homotethic of macrolaminate composite bulk materials. The failure of the coating is layer-by-layer, always exposing the ductile layer, which function is also to be a fuse that protect the remaining coating. The material of the interlayer and the period (interlayer/coating) selected resulted from the balance between the maximum performance of coating to avoid service failure and the minimum decrease of relevant mechanical properties of the monolitic hard coating as hardness.
Paula Maria Vilarinho
J. M. Castanho and M. T. Vieira, "Laminated Composite Thin Films: A Solution to Improve Cutting Tools Performance", Materials Science Forum, Vols. 514-516, pp. 1171-1175, 2006