Al-rich cubic Al0.8Ti0.2N coating with self-organized nano-lamellar microstructure: Thermal and mechanical properties

The synthesis of Al-rich cubic AlTiN coatings represents a challenging task. Recent advances achieved using chemical vapour deposition (CVD) demonstrated the possibilities to produce (i) cubic monophase coatings with Al ratio up to x = 90% and (ii) self-organized nano-lamellar AlxTi1 − xN coatings consisting of alternating wurtzite and cubic lamellae. In this work, a further development of the self-organized nano-lamellar CVD coating type is presented, namely the synthesis and physical properties of a purely cubic Al0.8Ti0.2N coating. The effect of the reduced Al content was investigated with respect to the coating's nano-lamellar microstructure, oxidation resistance, phase stability and nanoindentation hardness. Although the newly developed Al0.8Ti0.2N coating exhibited a slightly decreased oxidation resistance in comparison with the prior wurtzite-cubic nano-lamellar Al0.95Ti0.05N coating, the phase stability remained the same, while simultaneously a hardness increase of more than 30% was observed. This hardness of 36 GPa was stable up to 1050 °C, exhibiting a maximum value of 38 GPa around 950 °C. Furthermore, investigations by transmission electron microscopy revealed a modified arrangement of coherent nano-lamellae within columnar grains, forming an irregularly faceted layered coating morphology. In summary, the novel coating material grown with the rate of 5 μm per hour not only possesses a unique microstructure but attracts also by remarkable physical properties.