ICMCTF 2023 Session B4-4-TuA: Properties and Characterization of Hard Coatings and Surfaces IV

Boron carbide has attractive properties for use as ablator capsules for inertial confinement fusion (ICF). Creating an ultrathick, uniform, defect-free film on a rolling spherical substrate has many challenges, including delamination and fracture due toresidual stress and nodular growth defects, which are believed to originate from particulates deposited onto the film surface during growth. We have systematically studied effects of direct-current (DC) versus radiofrequency (RF) driven magnetron sputter deposition, substrate temperature, chamber pressure, and the target to substrate distance for amorphous boron carbide films deposited on stationary planar substrates. Here, we describe how these deposition parameters are optimized when the process is transferred to coating rolling spherical substrates.

This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344 and by General Atomics under Contract 89233119CNA000063.

Smart sensor technology is currently being developed and incorporated into several industries as part of the Industry 4.0 scheme to optimise energy input to industrial equipment thereby reducing carbon emissions.

These smart sensors applied on wheel bearings of EVs are prone to premature electrical failure due to current passage from dc/ac motors and also corrosion because of exposure to extreme environments. One of the solutions to this problem is developing electrically insulating and corrosion-resistant coatings that could be applied to the existing system. Current research is focussing on Al₂O₃-based coatings for these applications deposited using plasma spray/ electrolytic oxidation. However, Al₂O₃ coatings produced using the above methods were porous requiring additional sealing to be useful in insulation and corrosion-resistant applications. Therefore, Si-based coatings using µ-plasma enhanced chemical vapour deposition (PECVD) are being explored in this current study as the properties of silicon-based coatings can be varied through variations of nitrogen, oxygen, and silicon composition and the fact that PECVD is capable of producing denser coatings than PVD. In addition, higher deposition rates can be achieved using precursors such as hexamethyldisiloxane (HMDSO)/ hexamethyldisilazane (HMDSN) due to their high vapour pressures thereby reducing manufacturing cost.

In this study, HMDSO and O₂ gases were used to deposit SiO_x coatings at varying gas flow ratios (1:12, 1:16, 1:20), µ-powers (2 and 4kW) and coating thicknesses (3 - 10 μm) to study their impact on corrosion & insulation properties. Characterisation techniques such as Calo test, scratch testing, Rockwell C adhesion test, Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy, X-ray diffraction were used for characterisation. In addition, cyclic polarisation and electrochemical impedance spectroscopy were used for corrosion behaviour characterisation, and finally I-V measurements to ascertain insulation behaviour. Preliminary corrosion results of all the coated samples showed significant improvement in corrosion resistance compared to bare high-speed steel substrate. In particular, coatings deposited at 4kW (µ-power) and 1:12 (HMDSO:O₂) gas flow ratio had very low corrosion currents (a few pA) indicating high corrosion resistance.

In this study, (TiZrHfTa)N_x films were prepared through co-sputtering with four sputter guns. The stoichiometric ratio x of (TiZrHfTa)N_x films was varied by adjusting the reactive gas ratio of f_N2 (N₂/(N₂ + Ar)) at 0, 0.4, and 0.7. With an f_N2 of 0, the fabricated metallic Ti_0.23Zr_0.22Hf_0.30Ta_0.25 film, namely N00, exhibited a valence electron concentration of 4.25, a bcc phase with lattice constants of 0.3395 nm, a hardness of 8.0 GPa, and a Young’s modulus of 148 GPa. The introduction of N into the TiZrHfTa crystallites transformed the phase from bcc to fcc. N04 [(Ti_0.22Zr_0.30Hf_0.17Ta_0.31)N_0.83] and N07 [(Ti_0.33Zr_0.34Hf_0.13Ta_0.20)N_0.88] films were prepared whenf_N2 was set at 0.4 and 0.7, respectively. The N04 and N07 films exhibited a common fcc phase with lattice constants of 0.4490 and 0.4464 nm, respectively. The N04 and N07 films exhibited hardness values of 33.2 and 32.2 GPa and Young’s modulus values of 379 and 363 GPa, respectively. The corrosion resistance of (TiZrHfTa)N_x films was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy.