Microstructure development in Cr-Al-Si-N nanocomposites

M. Dopita ⁽¹⁾, D. Rafaja ⁽²⁾

¹Department of Electronic Structures, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, CZ-121 16 Prague, Czech Republic

²Institute of Materials Science, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 5, D-09599 Freiberg, Germany, dopita@mag.mff.cuni.cz

During the last years, the importance of thin films nanocomposites for technological applications increased rapidly. Nanocomposite thin films are considered as a suitable material for protection of cutting tools used in high temperature applications. The required properties of such thin films are, in particular, high hardness and good chemical stability at temperatures exceeding 1000°C.

In this contribution, we describe the microstructure development in the Cr-Al-Si-N nanocomposites with different [Cr]/([Al]+[Si]) ratio.

The Cr-Al-Si-N coatings were deposited using cathodic arc evaporation in nitrogen atmosphere with the working pressure of 1.3 Pa using two laterally rotating arc cathodes (p-80 from PLATIT) [35]. One cathode was made of chromium, the second one from aluminum containing 11 at % Si. The ion current on the Cr cathode was 80 A, on the Al-Si cathode 120 A. The bias voltage was -75 V. Polished plates of cemented carbide were used as substrates. The base pressure was 5 ´ 10^-3 Pa; the deposition temperature was approximately 450°C. In contrast to commercial coatings, the samples were not rotated during the deposition process, which offers the following advantages for microstructure studies. The expected preferred orientation of crystallites in Cr_1-xAl_xN is not superimposed by the sample rotation. A series of coatings with different chemical compositions can be obtained in one deposition process, as the chemical composition depends on the distance from the respective cathode.

The samples were investigated using electron probe microanalysis with wavelength-dispersive spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. The following topics are discussed in particular: phase stability of the Cr-Al-Si-N system, crystallite size, preferred orientation and crystallographic coherence of crystallites, the crystal anisotropy of the X-ray elastic constants and the interplay between the microstructure and the hardness.

Fig 1. HRTEM micrograph of the sample Cr_0.40Al_0.52Si_0.08N showing nanocrystallite particles

Fig 2. Sin²y-plot for the lattice parameter measured in the fcc phase of the sample Cr0.91Al0.08Si0.01N showing large crystal anisotropy of the lattice deformation. Open symbols show the lattice parameters obtained from the interplanar spacings of the lattice planes (111) and (200), filled symbols the lattice parameters measured using GAXRD on different lattice planes. For the GAXRD method, the diffraction indices are given at the bottom of the sin²y-plot

Acknowledgements.

This work is a part of the research plan MSM 0021620834 that is financed by the Ministry of Education of the Czech Republic.