The location and effects of Si in (Ti 1-x Si x )N y thin films
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cob Sjo¨le´n and Tommy Larsson Seco Tools AB, SE-737 82 Fagersta, Sweden
Slawomir Braun Division of Surface Physics and Chemistry, Department of Physics, Chemistry, and Biology (IFM), Linko¨ping University, SE-581 83 Linko¨ping, Sweden
Lennart Karlsson Seco Tools AB, SE-737 82 Fagersta, Sweden
Lars Hultman Thin Film Physics Division, Department of Physics, Chemistry, and Biology (IFM), Linko¨ping University, SE-581 83 Linko¨ping, Sweden (Received 23 November 2008; accepted 13 April 2009)
(Ti1–xSix)Ny (0 x 0.20; 0.99 y(x) 1.13) thin films deposited by arc evaporation have been investigated by analytical transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and nanoindentation. Films with x 0.09 are single-phase cubic (Ti,Si)N solid solutions with a dense columnar microstructure. Films with x > 0.09 have a featherlike microstructure consisting of cubic TiN:Si nanocrystallite bundles separated by metastable SiNz with coherent-to-semicoherent interfaces and a dislocation density of as much as 1014 cm2 is present. The films exhibit retained composition and hardness between 31 and 42 GPa in annealing experiments to 1000 C due to segregation of SiNz to the grain boundaries. During annealing at 1100–1200 C, this tissue phase thickens and transforms to amorphous SiNz. At the same time, Si and N diffuse out of the films via the grain boundaries and TiN recrystallize. I. INTRODUCTION
Materials science and advanced surface engineering are used to develop wear-resistant coatings for metal cutting tools with superior thermal properties, chemical inertness, and mechanical strength1,2 with the objective to enable higher cutting speeds with correspondingly higher working temperatures. Such a combination of material properties is sought for in ternary or quaternary ceramic coatings deposited by physical vapor deposition. In particular, the Ti–Si–N system exhibits interesting properties for metal cutting applications. Adding Si to TiN results in hardening for TiN–Si3N4 nanocomposites,3–5 TiN/SiNx multilayers,6–8 and metastable (Ti1–x Six)N solid solutions.9–11 The system, however, has no thermodynamically stable ternary phase. The NaCl-structure cubic (Ti1–xSix)N solid solutions are the least explored of the Ti–Si–N structures mentioned previously. Outstanding questions are for the occupational sites of Si in the TiN lattice and the corresponding saturation limit. The mechanisms of phase separation including a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0299 J. Mater. Res., Vol. 24, No. 8, Aug 2009
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element segregation and the nature of metastable SiNz phases forming coherent interfaces to TiN and their eventual transformation to a-Si3N4 also need clarification. The expected site for Si in TiN for the solid solutions is substitution for Ti. This supposition is supported by density functional theory (DFT) calculation tests assuming N2 atmosphere.12 For the upper limit of Si supersat
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