High temperature in-situ phase stability of sputtered TiAl_xN coatings

The temperature dependence of phase composition and lattice parameters, for TiAl_xN thin film coating, are experimentally investigated by in-situ synchrotron radiation X-ray diffraction (SR-XRD), at temperatures between 25 °C and 700 °C. Mechanical properties, such as: Young's modulus (E), hardness (H) and plastic deformation index (PDI) – were experimentally determined by nanoindentation, at 25 °C. Crystalline structural analysis, of SR-XRD results, indicates the major phases are TiN and AlN; with Ti₂O and TiO₂ phases also present above 600 °C. The lattice constants increased with an increase in temperature. Atomic and phase compositions, at 25 °C, were also verified by X-ray photoelectron spectroscopy (XPS). Field emission scanning electron microscopy (FESEM) images display an increase in surface roughness and reduction in grain size, with increasing Aluminium percentage (Al%). Nanoindentation analysis showed a maximum hardness of 25.1 ± 1.5 GPa (sample containing 12% Al), which was subsequently reduced upon addition of more Aluminium. Finite element modelling (FEM), including von Mises stress distribution, indicates lower mechanical integrity, for samples with high Al% content.