Deformation and fracture of TiN and TiAlN coatings on a steel substrate during nanoindentation L.W. Ma, J.M. Cairney, M.J. Hoffman, P.R. Munroe * Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia Received 12 August 2004; accepted in revised form 29 September 2004 Available online 11 November 2004 Abstract The deformation mechanisms and mechanical properties of both TiN and TiAlN coatings on a V820 nitridable steel substrate have been investigated. Deformation was induced by nanoindentation, and the microstructures of the indented regions were studied using various techniques, including focused ion beam (FIB) and transmission electron microscopy (TEM). Two coatings deposited using a cathodic arc process were investigated: a thicker (1.1 Am) TiAlN–TiN dual-layer coating and a slightly thinner (0.7 Am) TiN coating. Hardness was measured using nanoindentation using a 5-Am-radius spherical indenter. A model developed by Korsunsky et al. was used to obtain the hardness of the coatings, accounting for both the thickness of the coating and the influence of the substrate. Hardnesses of 30 and 24 GPa were obtained for the TiAlN and TiN coatings, respectively. Both coatings exhibited broadly similar mechanisms of deformation. Columnar cracking and shear steps at the coating–substrate interface indicated that coatings deform predominantly by shearing along the columnar grain boundaries; however, significant lateral edge cracking was also observed, especially in the case of the TiAlN coating. The interface between the TiAlN and TiN in the dual-layer coating did not appear to affect the deformation behaviour. D 2004 Elsevier B.V. All rights reserved. Keywords: TiN; TiAlN; FIB; TEM; Nanoindentation 1. Introduction The use of physical vapour deposition (PVD) hard coatings based on the transition metal nitride, titanium nitride (TiN), is well established. The coatings are com- monly applied to various kinds of steel cutting tools, forming tools, dies, etc. [1–4], providing surfaces with enhanced tribological properties in terms of low friction, high hardness and improved wear resistance [1–6]. How- ever, one disadvantage of TiN is in its application at high temperature, since it oxidizes rapidly at temperatures above ~550 8C, to form a layer that is partially composed of the rutile-structured TiO 2 [1,2]. In order to overcome such oxidation problems, ternary coatings, such as those based on titanium aluminium nitride (TiAlN), are becoming increas- ingly used because they show increased resistance to oxidation up to a temperatures of ~800 8C [7]. This is due to a dense protective layer of an aluminium-based oxide that is formed on the top of the (Ti,Al)N coating surface, which acts to inhibit further oxidation and improve high-temper- ature behaviour [7,8]. Furthermore, TiAlN is not only effective at improving high-temperature oxidation resist- ance, but also improves mechanical performance, through enhanced hardness and wear resistance [7]. It has been well documented in the literature that nanoindentation techniques can be effective in the evalua- tion of the mechanical properties, such as hardness and modulus, of hard coatings [9–12]. However, such techni- ques do not provide direct observation of the coating microstructure, in particular the mechanisms that may operate when the coating is deformed. In recent years, the focused ion beam (FIB) miller [13] has emerged as a materials characterization tool that may be used to observe the microstructure of thin films and coatings systems, including thin films that have been locally deformed. This 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.09.034 * Corresponding author. Tel.: +61 2 9385 4435; fax: +61 2 9385 6400. E-mail address: p.munroe@unsw.edu.au (P.R. Munroe). Surface & Coatings Technology 200 (2006) 3518– 3526 www.elsevier.com/locate/surfcoat