Microstructural size effects on the hardness of nanocrystalline TiN/amorphous-SiNx coatings prepared by magnetron sputtering |
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Authors: | Florian Kauffmann Veit Schier Thomas Beck Eduard Arzt |
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Affiliation: | a Max Planck Institut für Metallforschung, Heisenbergstr. 3, 70569 Stuttgart, Germany b Walter AG, Derendinger Str. 53, Postfach 20 49, 72072 Tübingen, Germany c Robert Bosch GmbH, Postfach 10 60 50, 70049 Stuttgart, Germany |
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Abstract: | It has been postulated that equiaxed nanocrystalline (<10 nm) TiN grains embedded in a thin amorphous silicon nitride (a-SiNx) phase are a prerequisite to obtain ultrahard TiN/a-SiNx coatings. The present study correlates hardness and microstructure of TiN/a-SiNx coatings with Si contents between 0 and 17 at.%. The coatings have been deposited by magnetron sputtering in industrial-scale physical vapour deposition systems. Transmission electron microscopy studies revealed that increasing the silicon content causes the TiN grain size to decrease. This is accompanied by a change in grain morphology: At Si contents lower than 1 at.% TiN grains become columnar, while at Si contents higher than 6 at.% equiaxed grains with diameters of 6 nm form. For silicon contents between 1 and 6 at.%, a transition region with nanocrystalline columnar grains exists. This nanocrystalline columnar microstructure causes maximum hardness values of more than 45 GPa for TiN/a-SiNx coatings as determined by nanoindentation. The elongated and equiaxed nanocrystalline TiN grains exhibit almost theoretical strength as dislocation-based deformation mechanisms are constrained. |
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Keywords: | 61 46 46 30 P |
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