TEM and DFT investigation of CVD TiN/;a;–Al₂O₃ multilayer coatings

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• 作者：S. Canovic ; S. Ruppi ; J. Rohrer ; A. Vojvodic ; C. Ruberto ; P. Hyldgaard ; M. Halvarsson
• 关键词：TiN ; ;a ; -Al₂0₃ ; γ ; – ; Al₂O₃ ; HREM ; FIB/SEM ; CBED ; Orientation relationship ; DFT
• 刊名：Surface and Coatings Technology
• 出版年：2007
• 期刊代码：106_02578972
• 类别：ms
• 出版时间：5 December 2007
• 卷：202
• 期：3
• 页码：522-531
• 文件大小：2445 K

摘要

This paper investigates the interfacial structure in hot-wall CVD TiN/;a;–Al₂O₃ multilayer coatings using both HREM and DFT modeling. Two multilayers with different thicknesses of the TiN layers (50 and 600 nm) separating the ;a;–Al₂O₃ layers are analyzed. The general microstructure of the two multilayers is relatively similar. The TiN layer in the thicker TiN/;a;–Al₂O₃ coating is thick enough to be several TiN grains high. This means that epitaxial columns, which are often found in the thinner TiN/;a;–Al₂O₃ coatings, are not present. However, the orientation relationships at the TiN/;a;–Al₂O₃ interfaces are the same in both multilayers. The HREM investigations show that ;a;–Al₂O₃ (001) planes can grow directly on flat (111) TiN faces, without any other phases or detectable amounts of impurities, such as sulphur, present. Where the TiN layers are more curved, γ–Al₂O₃ can be grown, at least partly stabilized by the cube-on-cube orientation relationship between γ–Al₂O₃ and the underlying TiN. The DFT calculations show very similar adsorption strengths for an O monolayer positioned on Ti-terminated TiC(111) and TiN(111) surfaces, with preferred adsorption in the fcc site. O adsorption on N-terminated TiN(111) is much weaker, with preferred adsorption in the top site. Calculated elastic-energy contributions yield a higher stability for ;a;–Al₂O₃ on TiN(111) than on TiC(111) and a higher stability for ;a;–Al₂O₃ than for α–Al₂O₃ on both TiC and TiN. This indicates that the observed higher stability of ;a;–Al₂O₃ on TiC(111) than on TiN(111) is not due to the lattice mismatch, while the preferred epitaxial growth of ;a;–Al₂O₃ over α–Al₂O₃ can be partly attributed to the mismatch.