Surface and Coatings Technology 163 –164 (2003) 515–520 0257-8972/03/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII:S0257-8972 Ž 02 . 00652-7 The effect of the substrate on the mechanical properties of TiN coatings S.V. Hainsworth*,W.C. Soh Department of Engineering, University of Leicester, Leicester LE1 7RH, UK Abstract TiN coatings are commonly used in industry to impart improved friction and wear performance. It is widely recognised that the substrate plays an important role in determining the mechanical properties and wear resistance of such coatings. TiN coatings are usually applied to hard tool steels where there is substantial load support from the substrate. However, there are many applications where it may be desirable to apply the coatings to substrates with lower hardness or stiffness values than the conventional, hard tool-steel substrates that are commonly used. Coatings can still be effectively used in these applications. However, it is then critical to understand the transitions between where the deformation is contained solely in the coating and where it is a combination of coatingysubstrate properties that are important in determining the overall mechanical response of the system. This paper therefore reports on a systematic investigation of the effect of the substrate on the mechanical response using a range of mechanical testing techniques. A TiN coating was deposited using ion-assisted PVD onto a number of substrates with differing combinations of modulus and hardness wi.e. a range of Young’s modulus (E) to yield stress (Y) EyY ratiosx. The mechanical properties of these coatings have been investigated using nanoindentation, microindentation and scratch testing, and the deformation was observed using scanning electron microscopy. In the microindentation tests, nested cracks were observed around the indentations. In the nanoindentation tests, the indentation response was found to be plasticity-dominated, with little evidence of cracking. The scratch tests showed that the scratch response was controlled by plastic deformation in the substrate, and that the friction coefficient increased as the depth of penetration into the sample increased. For the coatings here, it was observed that the indentation depthycoating thickness ratio required for the deformation to be contained within the coating was less than the usual ty10 ratio.  2002 Elsevier Science B.V. All rights reserved. Keywords: Substrate; TiN coating; Mechanical properties 1. Introduction TiN is a coating that is widely used for improving the tribological performance of materials w1–4x. The mechanical performance of the coating is strongly influ- enced by the substrate on which it is deposited w3x. Indentation techniques, including micro- and nanoinden- tation, and scratch tests, are commonly used for evalu- ating the mechanical performance of such coatings. The work described here aimed to perform a full evaluation of the mechanical properties of a TiN coating deposited onto a range of substrate materials with varying Young’s modulus (E) yyield stress (Y) EyY ratios. It is known that the yield strain EyY ratio influences the amount of material pile-up or sink-in around indentations, and that *Corresponding author. Tel.: q44-116-252-5692; fax: q44-116- 252-2525. E-mail address: svh2@le.ac.uk (S.V. Hainsworth). in particular, nanoindentation hardness and modulus calculations can be critically affected by the extent of the pile-upysink-in w5x. Recently, Saha and Nix w6x proposed a method for extracting film hardness and elastic modulus data using continuous stiffness measure- ments. This was based on a development of earlier work initially carried out by Joslin and Oliver w7x, and then by Page et al. w8x, who proposed using the parameter loadystiffness squared (PyS ) for investigating the elas- 2 tic properties of coated systems. The parameter loady displacement squared (Pyd ) has also been used to 2 investigate the transition from coating-only properties to properties of the coating and substrate, and in particular the hardness of coated systems w8–10x. This paper reports on an investigation into the mechanical properties of TiN coatings on a range of substrates with lower hardness andyor stiffness than conventional tool steels, and in particular, looks at the