CROSS-SECTIONAL TRANSMISSION ELECTRON MICROSCOPY OF DEFORMED MICROSTRUCTURES IN MONOLITHIC AND MULTILAYER TiSiN/TiN FILMS

The deformation microstructures generated by nanoindentation of multilayer coatings consisting of TiSiN layers alternating with ten TiN interlayers, were examined by cross-sectional transmission electron microscopy (XTEM). Two multilayered coatings were studied: a thin TiSiN coating interlayered with thick TiN interlayer and a thick TiSiN coating alternated with thin TiN layers. A monolithic TiSiN coating was also examined for comparison. Surface morphology of the samples was found to be variable. Both surface roughness and coating hardness increase with the thickness of the outermost TiSiN layer. All samples show columnar structures, and for the multilayer coatings, epitaxial growth of these columnar grains through the TiSiN/TiN multilayers was observed. Stair-shaped shear cracks can be seen in the multilayer coating alternated with thick TiN interlayers, whereas radial and edge cracks are observed in the coating multilayered with thin TiN layers and in the monolithic coating. TEM analysis also suggests that columnar grains help to resist the initiation of edge cracks. Compared to other studies on similar coating systems with fewer periods of interlayers, the deformation observed here appears less severe, indicating an improvement in the strength of the coating through increasing the number of interlayers.