Microstructural response of TiN monolithic and multilayer coatings during microscratch testing

Monolithic TiN and multilayered structures of TiN films that alternate with thin Ti interlayers were coated by filtered arc deposition onto a stainless steel substrate. Microscratch tests with a diamond indenter of 5-μm radius were carried out in combination with focused ion beam (FIB) sectioning and scanning and transmission electron microscopy to explore the controlling deformation mechanisms of these TiN coatings in relation to their microstructural design. It was found that for the monolithic TiN coating, columnar TiN grains slid against each other under normal forces and, at the same time, tilted under tangential forces. For the TiN multilayers, however, intercolumnar shear sliding was suppressed considerably by the multilayered structure and the interlayers, and grain tilting occurred largely within the upper TiN layer, presumably due to the shear effect of the soft Ti interlayers. With further increases in tangential force, rupture of TiN grains was observed within both types of coatings; for the TiN multilayers, rupture of TiN grains occurred predominantly within the layers close to the steel substrates. It can be concluded that the application of TiN multilayers provides better resistance to contact damage than the traditional monolithic TiN coatings did.