Deformation mechanisms of TiN multilayer coatings alternated by ductile or stiff interlayers

TiN multilayers that alternate with either titanium (ductile) or nanocomposite TiSiN (hard) interlayers were surface coated by filtered arc deposition onto stainless steel substrates. Hardness and deformation mechanisms of these multilayer coatings were investigated using depth-sensing indentation in comparison with traditional monolithic TiN coatings. A dual ion/electron beam microscope was used to analyse subsurface indentation damage. It was found that microstructural layering and the presence of interlayers in TiN multilayers jointly provided resistance to deformation by intercolumnar shear sliding, observed more evidently in the monolithic TiN coatings. This resulted in an increase in hardness, which also increased with both the number of layers and the presence of interlayers. Calculations based upon a mechanistic-based model revealed that the resistance by interlayers played a more important role than an increase in intergranular shear area due to the layered structure in resisting deformation. Compared with the titanium interlayer, the use of a hard nanocomposite interlayer increased the resistance to deformation; however, cracking occurred within both the TiN layers and the nanocomposite interlayers.