Self-organizing Ti-Si-B-C-N nanocomposite coatings for wear reduction

To meet the demand for tool surfaces with enhanced wear resistance, multiphase nanostructured thin films were investigated in recent years. The formation
of a nanocomposite structure, consisting of nanocrystalline (nc-) grains embedded in an amorphous (a-) matrix, results in high hardness values due to the Hall-Petch effect. Though high hardness values in these coatings are primarily achieved by nanocomposite structure, surface properties like oxidation and corrosion resistance display a stronger dependence on the a-matrix.
Coating deposition was carried out by plasma-enhanced chemical vapour deposition (PECVD) on quenched and tempered hot-work tool steel AISI H11 to form a homogeneous tribological protective layer with 2 to 5 micrometer thickness. The self organization in these so-called nanocomposite coatings, hindering the grains’ growth, is realized by spinodal phase segregation due to a miscibility gap between phases. In contrast to other methods that form nanostructured thin films, deposition rate is extraordinarily high (500 µm/h) due to self-organization.
High-resolution transmission electron microscopy (HR-TEM) showed a nanocomposite structure by the fact that grain orientation changes multiple times within
a dozen nanometers, as can be identified in Fig. 1.
The Ti-Si-B-C-N coating’s hardness is 24.9 ± 1.2 GPa. The starting point for oxidation is 800 °C, with sufficient oxidation resistance up to 850 °C. These results show, that high hardness and oxidation resistance can be combined, and potentially be used as protective coatings for tools in several hot forming applications, e.g. extrusion dies.