Narrow Results

Micro-arc oxidation technique (MAO) treatment produces a layer of alumina film on the surface of the aluminum alloy. A hard and uniform tetrahedral amorphous carbon film (diamond-like carbon, DLC) was deposited on the top of the alumina layer of the 2024 aluminum alloy by a pulsed filtered catholic vacuum arc (FCVA) deposition system with a metal vapor vacuum arc (MEVVA) source. The morphology and tribological properties of the duplex DLC/Al₂O₃ coating were investigated by a scanning electron microscope (SEM) and a ball-on-disk sliding tester. These results suggested that the duplex DLC/Al₂O₃ coating had good adhesion and a low friction coefficient, which improved significantly the wear resistance of aluminum alloys.

An infrared CO₂ laser was used for regional heating to study the heating effect on hot filament chemical vapor deposition of diamond-like carbon formation on Si(100) face substrates. The substrate surface temperature was about 450–500°C. The power of the laser called low, medium, and high raised the temperature of the substrate locally by 25, 45, and 55°C, respectively. At medium laser power, at the central laser beam region, a narrow Raman peak centered at 1438 cm^-1 was detected. It can be concluded that this region has good-quality DLC. This moderate high-frequency peak corresponds to a fourfold-rotation-symmetry atom in an amorphous carbon network from the tight-binding molecular dynamics simulation of Wang and Ho.

Diamond-like carbon, DLC, thin films which is an amorphous hydrogenated form of carbon, a-C:H, has been synthesized by CVD method. SEM imaging, back-scattering Raman spectroscopy and reflected FT-IR spectroscopy have been used for characterization of the synthesized thin films. Kramers–Kronig dispersion relations have been used for the calculation of dielectric and optical parameters, which include the real and imaginary parts of the refractive and dielectric indices. In Raman spectroscopy, two obvious, wide and almost symmetrical peaks around 1355 cm^-1 (D mode) and 1520–1550 cm^-1 (G mode), clarify the formation of a-C:H thin film. Reflected spectra of thin films, in the spectral region of 400–4000 cm^-1, have been recorded by the near normal FTIR reflection spectroscopy and show some peaks which can be assigned to the bending of sp³C–C, sp³ or sp²CH. The calculated data show that dielectric and optical parameters are almost independent of wavenumber.

Microarc oxidation (MAO) treatment produces a thick Al₂O₃ coating on the 15SiC_p/2024 aluminum matrix composite. After pretreatment of Ti ion implantation, a thin diamond-like carbon film (DLC) was deposited on the top of polished Al₂O₃ coating by a pulsed filtered cathodic vacuum arc (FCVA) deposition system with a metal vapor vacuum arc (MEVVA) source. The morphology and tribological properties of the duplex Al₂O₃/DLC multiplayer coating were investigated by Raman spectroscopy, scanning electron microscopy (SEM) and SRV ball-on-disk friction tester. It is found that the duplex Al₂O₃/DLC coating had good adhesion and a low friction coefficient of less than 0.07. As compared to a single Al₂O₃ or DLC coating, the duplex Al₂O₃/DLC coating on aluminum matrix composite exhibited a better wear resistance against ZrO₂ ball under dry sliding, because the Al₂O₃ coating as an intermediate layer improved load support for the top DLC coating on 15SiC_p/2024 composite substrate, meanwhile the top DLC coating displayed low friction coefficient.

An energy dissipation model was raised, including the influence of film properties, counterpart, contact stress and adhesion strength between film and substrate. A new plastic deformation-tendency index was introduced. The new index was more appropriate in predicting the wear behavior of a-C films than hardness and H/E. Particularly, the critical value of the new index existed for film failure in the friction test. Realizing the limitation of the model, some improvement directions of the model were also discussed in this study.

This study is focused on the tribological properties of micro- and nano-crystalline diamond (MCD and NCD), non-hydrogenated and hydrogenated diamond-like carbon (DLC and DLC-H) and nitrogen-based (CrN, TiN and TiAlN) coatings sliding against the super alloy Inconel 718, in terms of the maximal and average coefficients of frictions (COFs), the worn morphologies and the specific wear rates, by the rotating ball-on-plate configuration under dry condition. The results show that the nitrogen-based films show comparable COFs and wear rates with the WC–Co substrates. The DLC and DLC-H show lower COFs compared with the nitrogen-based films. Furthermore, their wear resistance is limited due to their low thickness compared with MCD and NCD, which have the same elemental composition. The DLC-H coating exhibits much lower wear rate compared with the DLC coating, which may be derived from the passivation of dangling bonds by the linking of H to C atoms. The MCD and NCD films show the lowest average COFs and mild wear after tribotests, due to their high hardness and low adhesive strength between pure diamond and the super alloy.

Among all the tested films, the NCD film-based tribopair presents the lowest maximal and average COFs, tiny wear debris particles, mild wear of ball and plate without scratching grooves, indicating that the NCD film may be suitable to be deposited on cutting tools for super alloy machining.