Superhard nanostructured ceramic–metal coatings with a low macrostress level

The macrostressed state of (Ti,Al)N–Cu and (Ti,Al)N–Ni ceramic–metal coatings obtained by the arc-PVD method has been studied using X-ray diffraction and by measuring the radius of curvature of a coating–base composite sample (Stoney's method). It is established that the presence of a tough metal phase favors significant reduction in the level of macrostresses in these structures as compared to those in (Ti,Al)N ceramic coatings, the absolute values of which decrease from 4.7–4.3 to 0.17–0.32 GPa. At the same time, both Ti–Al–Cu–N and Ti–Al–Ni–N coatings retain high hardness of 43 and 51 GPa, respectively, versus 29 GPa for Ti–Al–N coatings. The obtained results give grounds to suppose that the high hardness of the ceramic–metal coatings studied is determined by their nanocrystalline structure rather than by compressive macrostresses.