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Oxygen Impurities in TiSiN and Related Systems are Hindering the Phase Segregation , Formation of Stable Nanostructure and Degrading the Cutting Performance of Tools Coated with the Nanocomposites

We have shown earlier, that an oxygen impurity content of >0.4 at.% (4000 ppm) strongly degrades the hardness of the nc-TiN/a-Si3N4 nanocomposites. Here we show that such impurities also hinder the phase segregation and formation of stable and strong nanostructure consisting of 3-4 nm size TiN nanocrystals "glued" together by about 1 monolayer thick interfacial Si3N4-like layer, thus apparently stabilizing the solid solution at high temperature of >900°C, as reported by other researchers. At the impurity content of only few hundred ppm, the segregation is completed, and a stable nanostructure formed at temperature of ≤550°C. By decreasing the impurity content from 2000-3000 ppm down to about ≤1000 ppm in an industrial PVD coating equipment, the life time of cutting tools has been increased by a factor of ≥2. The results to be presented will underline the need for the improvement of the purity of the nanocomposite coatings applied in industry as well as used for fundamental studies in academia.