Nanocomposite PECVD multiphase coatings for wear reduction under thermal load conditions
With increasing demands for an enhanced service lifetime of tools, used in the hot form-ing and extrusion molding industry, new coating systems play an important role. Such applications demand a high thermal stability, high wear resistance, and low adhesion between the tool surface and hot metals (e.g. steel, aluminum, copper). Nanocomposite coatings consist of nm-size grains, embedded in an amorphous matrix. Due to their structure, they show a high hardness and wear resistance even under extreme conditions (high pressure, adhesive contact conditions, and high thermal loads). These multiphase coatings, generated from carbides, nitrides or borides of the transient metal titanium, provide the necessary properties for hot working applications. Currently, the binary and ternary phases TiN, TiC, TiB2 or TiCN, TiBN are commonly used, yet limited concern-ing their thermal stability. The element spectrum Ti-B-N, Ti-C-N is expanded with sil-icon to synthesize interesting quaternary or quinary systems with typical nanocomposite grain sizes of 3-7 nm. Recent in-situ phase analyses of the temperature-dependent phase transformation at 25 °C, 500 °C, and 750 °C revealed the possibility to optimize the mechanical properties by changing the structural composition in nanoscale dimensions. Tribological investigations under high-temperature conditions with a thermal load of 750 °C, and counterparts of Al2O3 spheres showed an improved wear resistance of the Si-containing systems compared to the non-Si systems. Assuming that Si and B contain-ing films have a suitable low adhesion to many materials, further work should investi-gate the adhesive properties towards hot metals, e.g. aluminum and copper for extrusion molding applications.