Influence of Si on the microstructure of arc evaporated (Ti,Si)N thin films;: evidence for cubic solid solutions and their thermal stability

Ti1-xSixN (0 <= x <= 0.14) thin solid films were deposited onto cemented carbide (WC-Co) substrates by arc evaporation. X-ray diffraction and transmission electron microscopy showed that all films were of NaCl-structure type phase. The as-deposited films exhibited a competitive columnar growth mode where the structure transits to a feather-like nanostructure with increasing Si content. Films with 0 <= x <= 0.01 had a < 111 > crystallographic preferred orientation which changed to an exclusive < 200 > texture for 0.05 <= x <= 0.14. X-ray photoelectron spectroscopy revealed the presence of Si-N bonding, but no amorphous Si3N4. Band structure calculations performed using a full potential linear muffin tin orbital method showed that for a given NaCl-structure Ti1-xSixN solid solution, a phase separation into cubic SiN and TiN is energetically favorable. The microstructure was maintained for the Ti0.86Si0.14N film annealed at 900 degrees C, while recrystallization in the cubic state took place at 1100 degrees C annealing during 2 h, 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 31.3 +/- 1.3 GPa and 44.7 +/- 1.9 GPa, respectively. The hardness was retained after annealing at 900 degrees C, while it decreased to below 3 0 GPa for 1100 degrees C following recrystallization and W and Co interdiffusion. (c) 2005 Elsevier B.V. All rights reserved.