Thermal expansion of magnetron sputtered TiCxN1-x coatings studied by high-temperature X-ray diffraction

The coefficient of thermal expansion (CTE) of TiCxN1-x can be adjusted by changing the value x between 0 (i.e. pure TiN) and 1 (pure TiC), which makes this material exceptionally useful as base layer to adapt the mismatch between the CTEs of substrate and coating. However, no comprehensive data on the CTE of sputtered TiCxN1-x has been reported up to now. Thus, in this work eleven coatings with compositions ranging from pure TiN to pure TiC were deposited using non-reactive magnetron sputtering. The elemental and phase composition were obtained by elastic recoil detection analysis and Raman spectroscopy, respectively. Powders of the coating material were analyzed using high-temperature X-ray diffraction between room temperature and up to 1000 degrees C to determine the temperature dependent lattice parameters. Subsequently, these lattice parameters were fitted using second order polynomials with coefficients linearly depending on the carbon content. Thus, a formula for the CTE of TiCxN1-x valid between 25 and 1000 degrees C was deduced which showed that at room temperature TiN has the highest CTE of 8.12 x 10(-6) K-1. The CTE gradually decreases with increasing carbon content to 7.55 x 10(-6) K-1 for pure TiC. While the value for TiC only shows a small increase with temperature, the CTE of TiN increases strongly up to 11.1 x 10(-6) K-1 at 1000 degrees C. The presented formula for the temperature dependent CTE of sputtered TiCxN1-x coatings allows to calculate the required composition for TiCxN1-x base layers, in order to tune their thermal expansion for the use in complex multilayered coatings.