ICMCTF 2022 Session B2-1-MoM: CVD Coatings and Technologies I

Diamond-like carbon (DLC) films, which is an amorphous carbon including both graphite (sp2 bond) and diamond (sp3 bond) structures, has widely used for hard mask for plasma etching and hard coating of the sliding parts. The DLC film containing rich sp3 bond realizes high hardness or low friction coefficient. A bombardment of carbon ions with incident energy of 100 eV into the film is essential to increase the sp3 bond in the DLC film. However, it is difficult to produce the high energy ions in conventional direct current magnetron sputtering (dcMS). High power impulse magnetron sputtering (HiPIMS) is attractive method to obtain large ion flux or high energy ions because the peak power density of HiPIMS is about 100 times larger than that of dcMS under same average power density. A DLC film on Si substrate deposited by HiPIMS shows the hardness of 20 GPa without negative substrate bias voltage[1]. A DLC film on plastic substrate has also deposited by HiPIMS without negative substrate bias voltage. The energy distributions of argon ion (Ar⁺) and carbon ion (C⁺) were measured using energy-resolved mass spectrometry in HiPIMS discharge in order to investigate the relationship between hardness and ion flux. The total ion flux of HiPIMS was about 100 times larger than that of dcMS under same average power density. The distribution of Ar⁺ was composed of low energy component and high energy component whereas C⁺ was mainly composed of high energy component. High energy component of both Ar⁺ and C⁺ simultaneously increased with increasing target voltage in comparison with low energy component of Ar⁺. The difference in IEDF is explained by the difference in production process of ions.

The hydrogen-free Si-DLC film was deposited by dual magnetron sputtering method using carbon and silicon targets. The friction coefficient measured with the ball on disc test decreased to be 0.074 with increasing the Si content in the DLC film. At this experimental condition, the hardness was 18.4 GPa measured by the nano-indenter. Si-C bond increased with increasing the Si content from C1s spectra of XPS analysis. The relation among sp3 fraction, hardness, and behaviors of ions will be discussed.

reference

[1] K. Iga et al., Thin Solid films, 672, 104 (2019).

MAX phases have a unique combination of ceramic and metallic properties that make them excellent candidate materials for high temperature applications. They are particularly interesting for their excellent thermal stability up to 1500 °C, their exceptional thermal shock resistance and their damage tolerance. In addition to their good mechanical properties at elevated temperatures and high stiffness, they exhibit optical, electrical and thermal properties similar to metals.

In this work, we report on the preparation of multilayer ceramic coatings based on MAX Phases by Reactive Chemical Vapor Deposition (R-CVD), able to withstand high temperature (T>1000°C) under air while maintaining their structural and functional properties. Computational Fluid Dynamics calculations, thermodynamic and diffusion considerations were developed for the selection and the design of the multilayer experiments.

R-CVD depositions were conducted in a vertical quartz cold-wall CVD reactor in the system TiCl_x - H₂ - SiH₄ - C₃H₈ - H₂ between 1100-1300 °C in order to form multi-layer coatings that consist of stacks of titanium silicon carbide (MAX phase layer Ti₃SiC₂) and silicon carbide (SiC).

The surface morphology and cross-sectional microstructure of as-grown Ti₃SiC₂–SiC layers were characterized by Scanning Electron Microscopy (SEM), and X-Ray Diffraction analysis to identify the different solid phases. High temperature oxidation tests, nano-indentation and emissivity measurements were carried out with the aim of evaluating the potential of this material for high temperatures applications.

There is a constant need to improve the performance of metal cutting tools. A materials research approach is the chemical vapor deposition (CVD) of coatings on the tool insert to enhance some of its properties or to introduce new functionalities. Hexagonal WC is the hard component of cemented tungsten carbide and is expected to have a good performance as a coating as well. Tungsten based coatings deposited by chemical vapor deposition are, however, so far relatively unexplored. The deposition from the gas phase can introduce new microstructures and textures, leading to enhanced mechanical properties. Moreover, the coating is expected to be under a compressive stress after post-deposition cooling if the substrate contains Co and the coating only the hexagonal WC phase. This differs from a tensile stress causing cracks in many conventional CVD coatings on cemented carbide.

The aim of this research was to deposit a new CVD coating, tungsten carbonitride (W(C,N)), which is a solid solution of hexagonal WC and WN, onto cemented carbide. Hexagonal WC and WN are line phases and are difficult to obtain by CVD due to the discrepancy in the reactivity of W-halide and C-precursors or a stable cubic WN_1-x phase, respectively. For the W(C,N) synthesis WF₆, CH₃CN and H₂ were used and they proved to have a balanced reactivity for W, C and N incorporation in ratios that enabled the formation of the hexagonal phase.

First, the current understanding on the growth mechanism will be presented. The results are based on a kinetic study and the influence of the process parameters on the coating microstructure and composition. Correlations between the grain size, morphology and orientation will be shown. The coating microstructure was characterized by scanning electron microscopy (SEM), the composition by elastic recoil detection analysis (ERDA) and the texture by X-ray and electron backscatter diffraction (XRD and EBSD). Transmission electron microscopy (TEM) was used to investigate a preferred prismatic texture and the type of defects introduced during the growth. Hard X-ray Photoelectron Spectroscopy (HAXPES) was used to investigate the reason behind a (C+N)-rich composition.

Further, the possibilities to tailor the microstructure and grain orientation of the coatings will be discussed. Nanoindentation measurements, diamond scratch and abrasion tests showed that the coatings were hard or superhard and their mechanical and tribological properties were dependent on the above properties.