Microstructural response of TiN monolithic and multilayer coatings during microscratch testing
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A. Bendavid and P.J. Martin Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) Industrial Physics, Lindfield, NSW 2070, Australia (Received 21 March 2007; accepted 3 May 2007)
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-m 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.
I. INTRODUCTION
TiN coatings have been used to improve wear resistance of metallic materials in a wide range of engineering applications, such as cutting and forming tools. With advances in electron microscopy, mechanical testing and computer modeling techniques, keen interest has been generated in understanding the mechanical properties and deformation mechanisms of TiN coatings.1–7 More recently, using site-specific cross-sectional electron microscopy, the influence of microstructural design on the mechanical behavior of columnar-grained TiN coatings has been evaluated. Intergranular shear sliding has been identified to be the dominant mechanism under indentation deformation.1,2 Moreover, important factors such as intergranular shear stress,1,2,7 residual stress,5,7 structural layering (i.e., multilayers with either hard or soft interlayers),8 and mechanical properties of substrates3,7 have been found to influence the behavior of TiN coatings in relation to indentation damage.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0292 2312 J. Mater. Res., Vol. 22, No. 8, Aug 2007 http://journals.cambridge.org Downloaded: 18 Mar 2015
In contrast to the detailed understanding regarding the indentation behavior of TiN coatings in recent years, investigation of scratch damage on these coatings has been limited. Scratch tests are understood to play an equally, if not more, important role in investigating the tribological performance of hard coatings, since scratch tests simulate mechanical wear process
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