Growth and Characterization of Ti-Si-N Hard Coatings
Sammanfattning: Metastable (Ti,Si)N alloy and TiN/SiNx multilayer thin solid films as well as SiNx/TiN surfaces have been explored. Cubic Ti1-xSixN (0?x?0.14) films deposited onto cemented carbide (WC-Co) substrates by arc evaporation exhibited a competitive columnar growth mode where the structure transforms to a feather-like nanostructure with increasing Si content as revealed by x-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy revealed the presence of Ti-N and Si-N bonding, but no amorphous Si3N4. Band structure calculations showed that phase separation of NaClstructure Ti1-xSixN solid solution into cubic SiN and TiN phases is energetically favorable. The metastable microstructure, however, was maintained for the Ti0.86Si0.14N film annealed at 900°C, while recrystallization in the cubic state took place at 1100°C annealing during 2h. The Si content influenced the film hardness close to linearly, by combination of solid-solution hardening in the cubic state and defect hardening. For x=0 and x=0.14, nanoindentation gave a hardness of 29.9±3.4 GPa and 44.7±1.9 GPa, respectively. The hardness was retained during annealing at 900°C.Nanostructured materials, e.g., nanocomposites and nanolaminates, are defined by internal interfaces, of which the nature is still under debate. In this work two-phase model systems were explored by depositing SiNx/TiN nanolaminate films, including superlattices containing cubic SiNx, by dual target reactive magnetron sputtering. It is demonstrated that the interfacial phase of SiNx onto TiN(001) and TiN(111) can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, it is found that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for novel nanostructured materials.
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