High thermal stability of TiAlSiCN coatings with "comb" like nanocomposite structure

The aim of this work was to understand the reasons for the exceptionally high thermal stability of the TiAlSiCN coatings. The hardness of the coatings increased from 41.5 to 43 GPa between 25 and 900 degrees C, reached a maximum value of 49 GPa at 1000 degrees C, and then decreased to 37 GPa at 1300 degrees C. The structural investigations performed before and after annealing at 1000, 1200, and 1400 degrees C using X-ray diffraction, scanning and transmission electron microscopy (TEM), and high-resolution TEM showed that the as-deposited "comb" like nanocomposite structure, in which (Ti,Al)(C,N) columnar grains, 10-30 nm wide, were separated by a well developed amorphous tissue, possessed a very high thermal stability as its dominant cubic phase was stable in the temperature range of 25-1400 degrees C. Further thorough characterization by means of energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy revealed structural modifications inside crystalline and amorphous phases during annealing in vacuum. Such modifications associated with a short-range rearrangement of elements are shown to be responsible for the high hardness of the TiAlSiCN coatings observed up to 1300 degrees C, with peak hardness at 1000 degrees C. (C) 2012 Elsevier B.V. All rights reserved.