ICMCTF 2021 Virtual Conference Session B3: Deposition Technologies and Applications for Diamond-like Coatings

Diamond-like carbon is a popular hard coating material whose properties widely depend on deposition process and conditions within the process. Variations between the methods and conditions yield films with varying hydrogen, sp2 carbon, and sp3 carbon content who have densities between 1 and 3 g/cc, spanning the difference between a low-density hydrocarbon polymer and polycrystalline diamond (high density carbon). This material is becoming increasingly interesting as a new ablator material for inertial confinement fusion because it is low Z and has the potential to tune its density between that of glow discharge polymer(~1 g/cc) and diamond (3.5 g/cc), two ICF ablator materials of choice. This work investigates the use of a magnetized hollow cathode discharge for depositing thick, density tunable amorphous carbon films for future inertial confinement fusion experiments.A variety of the properties of the films will be discussed including: composition, density, impurity content, thickness limitation, deposition rate and surface morphology.

IM Release: LLNL-ABS-814679

DLC coatings are becoming well established across many industrial sectors including aerospace, automotive, oil and gas, and cold forming tools. While DLC coatings exhibit good mechanical properties and low coefficient of friction for themselves, DLC coating–substrate systems may suffer from insufficient wear resistance. This paper describes the wear mechanisms and reports characteristics of the DLC coating-steel substrate system behaviour after mechanical and thermochemical steel substrate pre-treatments. We have investigated two tool steel substrates, Sverker 21 (AISI D2) and advanced powder metallurgy alloyed steel Vanadis 8. Initially, the substrates were heat treated in vacuum furnace and gas quenched resulting in hardness of 59±1 and 64±1 HRC respectively. Subsequently the samples were subjected to mechanical turning and burnishing with 130N and 160N forces, using diamond composite tools with ceramic bonding phase. Afterwards, a vacuum nitriding process in a PVD chamber as a pre-treatment for subsequent DLC coating deposition was carried out. Coated samples were subjected to a series of ball-on-disc wear tests against Al2O3 and Si3N4 counterparts. X-ray diffraction (XRD), instrumented indentation and scanning electron microscopy (SEM) were employed to examine the phase composition, nano-hardness, Young’s modulus, surface microstructure, elemental distribution and 3D surface topographies of the wear scars. Selected variable factors including the type of steel, the burnishing force, type of counter-body material were subjected to statistical analysis. The effect of sequential processes used as pre-treatment on DLC coating durability was demonstrated and the results are discussed in light of improving the cold forming tools tribological performance.

Keywords: DLC coatings, tool steels, vacuum nitriding, slide burnishing

Hydrogen-free ta-C coatings are already used to reduce friction in lubricated environments. The application under minimum quantity lubricated and non-lubricated boundary conditions remains a great challenge. The addition of the dry lubricant MoS₂ is intended to improve the performance characteristics of the ta-C in this case. For the production of ta-C coatings, the Laser Arc process is particularly suitable, with which very hard and low-defect coatings can be produced. MoS₂ targets can be combined and alternately evaporated using the same technique.

In this work, we studied the effect of target poisoning ratios of tungsten carbide films using a superimposed HiPIMS and MF system. The flow rate of the acetylene (C₂H₂) was controlled using a plasma emission monitoring (PEM) system to feedback control the target poisoning ratio during deposition. Five coatings, WC10, WC30, WC50, WC70 and WC90, were grown under target poisoning ratios of 10%, 30%, 50%, 70% and 90% respectively, on Si, AISI420 stainless steel (SS) and AISI304 SS substrates. A small hysteresis loop area for the emission intensity of W at 429.6 nm was observed with variation of C₂H₂ gas flow rates. With increasing target poisoning ratios, the phases changed from nanocrystalline β-WC_1-x to amorphous. The X-ray photoelectron spectroscopy was used to study the chemical bindings of coating. The highest power normalized deposition rate of 25.20 nm min^-1kW^-1 was observed for WC90. The highest hardness value of 32.3 GPa was measured for WC30. WC50 showed the best adhesion among the coatings with L_C2 value of 65.1 N. The lowest COF of 0.26 was observed for WC90. In potentiodynamic polarization test using 0.1M H₂SO₄ solution, WC90 showed colourful fringes around the corrosion micro-pits with the highest polarization resistance (R_p) of 4552.51 kΩcm².

Keywords: Superimposed high power impulse magnetron sputtering, middle frequency, WCx coatings, tungsten doped diamond-like carbon coating, target poisoning, nanoindentation, tribometer

Titanium carbide (TiC) coatings have attracted wide attention from researchers and industry due to their high hardness, good wear and corrosion resistance. In this study, the TiC coatings were fabricated by four different power supply systems including superimposed HiPIMS-MF, HiPIMS, MF, and DC in a gas mixture of acetylene and argon. During the deposition process, a plasma emission monitoring (PEM) system was used to control the Ti target poisoning status to 70%. The single crystal silicon wafers and AISI304 stainless steel plates were used as substrates. The chemical compositions of TiC films were analyzed by a field emission electron probe microanalyzer. The microstructure of thin film was examined by a field emission scanning electron microscope. The crystalline structure of thin film was analyzed by an X-ray diffractometry. The hardness, adhesion and tribological properties of TiC films were evaluated by nanoindenter, scratch test and pin-on-disk wear test, respectively. The corrosion resistance of TiC films in 0.1 M H₂SO₄ aqueous solution was examined by an electrochemical workstation. The influence of four different power supplies on the deposition rate, microstructure, hardness, adhesion, wear and corrosion resistance of TiC films were studied in this work. Although the deposition rate of the TiC coating deposited by DC power supply was the highest, the film quality was inferior to other films due to its less dense microstructure. On the other hand, the TiC coating fabricated by superimposed HiPIMS-MF power supply exhibited a dense microstructure, good mechanical property and excellent corrosion resistance.