TEM investigation of TiAlN/CrN multilayer coatings prepared by magnetron sputtering M. Panjan ⁎ , S. Šturm, P. Panjan, M. Čekada Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia Available online 2 June 2007 Abstract Multilayer coatings TiAlN/CrN were deposited by reactive magnetron sputtering. Thickness of the individual layers varied from 2 nm to 25 nm while the total thickness of the coating was ∼ 5 μm. Coatings in cross-section were investigated using conventional, scanning and high-resolution transmission electron microscopy (TEM). Conventional TEM studies revealed a columnar microstructure. Chemical analysis of individual layers was preformed by high-angle annular dark-field scanning TEM (HAADF-STEM). The layers were well separated and no substantial intermixing was observed. High resolution TEM and electron diffraction studies showed that TiAlN and CrN layers are crystalline with B1 NaCl-type crystal structure. Coherent interfaces between TiAlN/CrN were observed, which can be attributed to a small mismatch between lattice parameters. In some areas between steel substrate (bcc-Fe) and the coating epitaxial relationship {001} Fe ||{001} coating and b100N Fe ||b110N coating was observed. In different areas of the coating TiAlN layers appeared to be less crystalline than CrN. © 2007 Elsevier B.V. All rights reserved. Keywords: TiAlN/CrN; Multilayer; Magnetron sputtering; TEM; STEM; HRTEM 1. Introduction Combination of different materials in a form of multilayers produces coatings with superior properties than in the form of a single layer. Especially good properties are found for nitride materials with a few nanometer thick layers. These multilayers, also termed superlattices, exhibit higher hardness, better toughness, wear and oxidation resistance than constituent materials deposited in a single layer. In the past years a variety of different nitride multilayer coatings have been produced, for example: TiN/CrN [1,2], TiN/NbN [3,4], AlN/VN [5], TiAlN/ CrN [6,7]. All of these coatings reach maximum hardness in a narrow range of bilayer thickness of ∼ 3–10 nm. The maximum hardness is always significantly higher than the hardness of the materials in each layer. Several explanations have been proposed for the origin of this effect including dislocation blocking by layer interfaces, Hall–Petch strengthening, strain effects at layer interfaces, and the supermodulus effect [8]. One of the most studied materials in the hard coating technology are TiAlN and CrN. Properties of TiAlN depend on the content of aluminum [9]. At the approximate 1:1 ratio of titanium and aluminum atoms it is possible to get hardness higher than 30 GPa [10]. TiAlN has very good oxidation resistance compared to TiN [6]. CrN has lower hardness (∼ 18 GPa) but it is tougher and thermally more stable [11]. Combination of these two materials therefore yields a coating with good mechanical, wear and oxidation properties [6,12]. The maximum hardness of TiAlN/CrN superlattice was shown to be about 39 GPa for a bilayer period of 6 nm [6]. Our aim was to investigate microstructure, crystal structure and interfaces of TiAlN/CrN coating using cross-sectional transmission electron microscopy (TEM). TEM is the only technique with sufficient spatial resolution to resolve nanometer- size layers in superlattices. Conventional TEM gives us detailed information on microstructure, including grain size, orientation and texture as well as on the types and distribution of defects (dislocations, stacking faults). On the other hand, high-resolution TEM (HRTEM) offers information on atomic scale with pos- sibility to locally determine crystal structure and to study interface characteristics (coherency, morphology, epitaxial relationships between the layers). In spite of an immense number of papers published on PVD coatings TEM investigations of such structures are still relatively rare and detailed structure of PVD coatings on Available online at www.sciencedirect.com Surface & Coatings Technology 202 (2007) 815 – 819 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Tel.: + 386 1 477 3276; fax: +386 1 251 9385. E-mail address: matjaz.panjan@ijs.si (M. Panjan). 0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2007.05.084