Identification of the Si3N4-like grain boundary tissue phase by TEM

Identification of the Si3N4-like grain boundary tissue phase by TEM methods in ncTiSiN hard coating deposited by unbalanced magnetron sputtering
B. Pécz1 , P.B. Barna1, I. Kovács1, G. Radnóczi1, and S. Veprek2
MTA TTK, Research Institute. for Technical Physics and Materials Sciences,
Budapest, Konkoly-Thege u. 29-33, Hungary
Department of Chemistry, Technical University Munich, Lichtenbergstr. 4, D-85747
Garching, Germany
It has been early identified that the high hardness (>30 GPa) of functional surface
coatings (more general is the Si doped TiN) required in the various fields of application can
be provided by nanocomposite film structures in which the nanocrystals are encapsulated by a
thin layer of a second phase. Beside the crystal size (5-10nm) the nature (thickness, structure,
level of oxygen contamination) of the interfacial layer is the most decisive to control the
hardness1. One of the main challenge facing electronmicroscopists is to determine the
thickness and structure/chemistry of the Si3N4-like tissue phase situated in the nanocurved
interfaces between the TiN nanocrystals with the knowledge of theoretical calculations that
the optimal thickness could be in the range of some ML. In the present study we localized the
Si3N4-like interfacial layer and determined its thickness in the nanocomposite TiN/ Si3N4
coating doped with 6,4 at% Si. It has been concluded that the TiN single crystals identified by
lattice fringe imaging are encapsulated by the Si3N4-like interfacial layer and its thickness is
in the range of 1-2 nm. The size of single crystals (10 – 150 nm) is larger than the grain size
determined by XRD analysis (6-8nm). Conventional and high resolution transmission electron
microscopy and selected area electron diffraction were applied to determine the
microstructure. The Si3N4-like interfacial layer was investigated by electron energy loss
spectroscopy (EELS). The cross sectional (XTEM) and plan view specimens of the 6,4 μm
thick TiN/ Si3N4 coating deposited on stainless steel substrate have been prepared by the ion
beam thinning technique developed by A. Barna.
P. Nesladek and S. Veprek, Phys. Stat. Sol. (a) 177 (2000)53