Ti-Si-B-C-N plasma enhanced chemical vapor deposition nanocomposite coatings for high temperature applications

Abstract

With increased demands for service lifetime of tools in hot forming applications, e.g. hot extrusion and die-casting, surface modifications of hot working steels are necessary to improve the surface's thermal stability and oxidation resistance. The machining of aluminum and copper is especially challenging, considering its tendency to stick at the tools’ surface, which is increasingly impactful at elevated temperatures. Developing Ti-Si-B-C-(N) nanocomposite coatings with plasma-enhanced chemical vapor deposition is a promising approach to overcome these deficiencies, because, with an adequate Si-content, thermal stability and oxidation resistance can be increased by forming a thin, amorphous Si3N4 tissue layer between the nanocrystalline grains of the coating. In this study, the influence of nitrogen on the coatings’ thermal properties is under investigation for N-content in the range between 0.0 at.-% and 14.6 at.-%. Different oxidation resistance in dependence of the N-content was observed at high temperatures (T = 750-900 °C) in-situ by X-ray diffraction in air. The multiphase coatings form compositionally complex nanostructures with an average grain size of ca. 4 to 7 nm. The hardness is strongly affected by nanocomposite structure and residual elements like O and Cl incorporated during coating deposition, whereas the influence of N-content on Ti-Si-B-C-(N) coatings is less significant regarding mechanical properties. Considering the thermal properties, the N-content has been proven to be of central importance. Oxidation was observed in the range between 800 °C and 900 °C, underlining the possible application as protective coating for hot forming tools.