Surface and Coatings Technology 177–178 (2004) 325–333 0257-8972/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2003.09.043 Temperature dependence of structure and mechanical properties of Ti–Si–N coatings X.D. Zhang , W.J. Meng *, W. Wang , L.E. Rehn , P.M. Baldo , R.D. Evans a a, a b b c Mechanical Engineering Department, Louisiana State University, Baton Rouge, LA 70803, USA a Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA b Timken Research, The Timken Company, Canton, OH 44706, USA c Abstract Characterization of structure and mechanical properties of Ti–Si–N coatings deposited by a high-density plasma assisted vapor deposition technique at ;250 8C was carried out and compared to Ti–Si–N coatings deposited at ;700 8C. The nanoscale structure of Ti–Si–N coatings was probed by combining transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS). The structural characterizations showed that the present Ti–Si–N coatings consists of nanocolumnar B1- TiN grains interdispersed within an amorphous silicon nitride (a-Si:N) matrix, independent of the deposition temperature. Significant Ti atom dissolution within the a-Si:N matrix was observed, and increasing the deposition temperature from ;250 to ;700 8C decreases the Ti dissolution limit. The influence of the extent of the TiNya-Si:N phase separation on the mechanical properties of Ti–Si–N coatings is probed by instrumented nanoindentation. The extent of phase separation was found to significantly influence the mechanical properties, with the hardness of Ti–Si–N coating deposited at ;700 8C reaching ;40 GPa. The present results illustrate the sensitivity of mechanical properties of ceramic nanocomposite coatings on the detailed nanoscale structure.  2003 Elsevier B.V. All rights reserved. Keywords: Mechanical properties; Ti–Si–N coatings; Deposition temperature dependent nanostructure 1. Introduction Since the initial report of hardness exceeding 50 GPa in Ti–Si–N coatings w1x, the structure and mechanical properties of this coating system have been extensively studied w2–4x. Interest in the Ti–Si–N system has been further elevated by a report of hardness reaching and exceeding that of diamond w5x. These reports motivated the desire to better define the nanoscale coating structure necessary to achieve such superstrengthening effects. To this end, our previous studies on Ti–Si–N coatings deposited at ;250 8C showed that not all ceramic nanocomposite coatings consisting of nanocrystalline TiN grains embedded in an amorphous silicon nitride (a-Si:N) matrix exhibit superstrengthening w6x. Using an inductively coupled plasma (ICP) assisted hybrid chemical yphysical vapor deposition (CVDyPVD) tech- nique, a series of Ti–Si–N coatings was deposited on *Correspoding author. Tel.: q1-225-578-5832; fax: q1-225-578- 5924. E-mail address: wmeng@me.lsu.edu (W.J. Meng). Si(100) substrates. These Ti–Si–N specimens, with Si compositions ranging from 0 to 20 at.%, were shown to consist of mixtures of nanocrystalline TiN and a-Si:N. Their hardness was found to be no more than 32 GPa. Because of the refractory nature of the Ti–Si–N system, the process of TiNya-Si:N phase separation may be influenced by surface kinetics during deposition, which are expected to be temperature dependent. Given the thermodynamic driving force for Ti–Si–N to phase separate w7x the deposition temperature can influence the actual extent of phase separation. Our previous studies suggested little Si dissolution into B1-TiN w8x. The extent of Ti dissolution into the a-Si:N matrix was, however, not studied. We report in the present paper quantitative measure- ments of Ti dissolution into a-Si:N in Ti–Si–N coatings deposited at ;250 8C and ;700 8C. Coating compo- sition, structure and atomic short-range order surround- ing Ti atoms have been probed by combining Rutherford backscattering spectrometry (RBS), transmission elec- tron microscopy (TEM) and X-ray absorption near edge