Adhesion improvement of hydrogenated diamond-like carbon thin films by pre-deposition plasma treatment of rubber substrate

For reduction of friction and enhancement of wear resistance of dynamic rubber seals, thin films of hydrogenated diamond-like carbon (DLC) have been deposited on hydrogenated nitrile butadiene rubber (HNBR) via magnetron-enhanced plasma chemical vapor deposition (ME-PCVD). Pre-deposition plasma treatment of HNBR substrate is proved to be crucial for the improvement of film performance due to enhanced interfacial adhesion. The columnar structure and the crack network formed during deposition enhance the flexibility of DLC thin films and exhibit strain tolerance up to 5%. Below 50% stretch strain and after unloading, thin DLC films of ∼ 300 nm thickness still adhere on the rubber substrates and no spallation or delamination is observed. The thin DLC film deposited on Ar-plasma pre-treated rubber at − 400 V substrate bias potential exhibits a very low coefficient of friction of 0.175 (compared to > 1 of uncoated HNBR rubber). After tribotests even under high normal load of 3 N, almost no wear can be seen on the films. Such tribological property is even better than that of 1 µm thick DLC or Me-DLC coated rubbers.     

Influence of carbon sputtering power on structure, corrosion resistance, adhesion strength and wear resistance of platinum/ruthenium/nitrogen doped diamond-like carbon thin films

Platinum/ruthenium/nitrogen doped diamond-like carbon (PtRuN-DLC) thin films were deposited on conductive p-Si substrates using a DC magnetron sputtering deposition system by varying carbon sputtering power. The chemical composition, bonding structure, surface morphology and adhesion strength of the PtRuN-DLC films were investigated using X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, atomic force microscopy (AFM), and micro-scratch test, respectively. The corrosion behavior of the PtRuN-DLC films in a 0.1 M NaCl solution was investigated using potentiodynamic polarization test. The corrosion results indicated that the corrosion resistance of the PtRuN-DLC films increased with increased carbon sputtering power probably due to decreased porosity level in the films with increased growth rate and film thickness. The wear performance of the PtRuN-DLC films was investigated with a ball-on-disc micro-tribometer. It was found that the increased carbon sputtering power significantly improved the wear performance of the films by enhancing the adhesion strength of the films.     

Microstructure and tribological properties of diamond-like carbon and TiAlSiCN nanocomposite coatings

Diamond-like carbon (DLC) and TiAlSiCN nanocomposite coatings were synthesized by multi-plasma immersion ion implantation and deposition. The DLC content in the composite coating was controlled by the flow ratio of N₂ to C₂H₂ during the deposition process. The microstructure and tribological properties of the as-deposited coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), nanoindentation and ball-on-disk friction tests. The TEM results show that all the DLC-TiAlSiCN coatings had a two phase composite structure of the TiCN nanocrystals embedded in an amorphous matrix consisting of a-Si₃N₄, a-SiC, a-CN and DLC. TEM observations also reveal that the spacing between the adjacent nanocrystals increases with DLC content. In addition, the DLC-TiAlSiCN nanocomposite coating with a small crystalline spacing of about 0.6 nm shows a higher hardness up to 50 GPa and a larger friction coefficient. An increase in the DLC content of the coating benefits its friction coefficient while its hardness decreases. The friction coefficient reduces to 0.14 when the DLC content is about 31%.     

Mechanical properties of silicon-doped diamond-like carbon films prepared by pulse-plasma chemical vapor deposition

Silicon-doped diamond-like carbon (Si-DLC) films were prepared by dc pulse-plasma chemical vapor deposition (CVD), using a mixture of acetylene (C₂H₂) and tetramethylsilane (TMS) as the material gas. The pulse voltage was varied from − 2 to − 5 kV, and the TMS flow ratio (TMS/(C₂H₂ + TMS)) was varied from 0 to 40%. At a pulse voltage of − 2 kV, an increase in TMS flow ratio leads to a decrease in hardness. In contrast, at a pulse voltage of − 5 kV, an increase in TMS flow ratio leads to a slight increase in hardness. The high hydrogen concentration in the films due to an increase in TMS flow ratio promotes the formation of polymeric sp³ C―H bonds, resulting in the fabrication of soft films at a low pulse voltage of − 2 kV. However, an increase in the effect of ion peening on the growth face results in the formation of hard films at a high pulse voltage of − 5 kV. Then, at a pulse voltage of − 5 kV fabricating hard Si-DLC films, an increase in TMS flow ratio leads to an increase in the silicon content in the films, resulting in a decrease in the friction coefficient. Therefore, it is clarified that Si-DLC films fabricated by dc pulse-plasma CVD under a high pulse voltage and high TMS flow ratio exhibit high hardness and a low friction coefficient. Moreover, to investigate the friction coefficient of Si-DLC films fabricated by dc pulse-plasma CVD, films deposited by dc plasma CVD were also evaluated. To obtain the same low friction coefficient, dc pulse-plasma CVD requires less TMS than dc plasma CVD. Hence, it is also clarified that Si-DLC films can be fabricated at a low cost by dc pulse-plasma CVD.     

Structure, scratch resistance and corrosion performance of nickel doped diamond-like carbon thin films

Nickel doped diamond-like carbon (DLC:Ni) thin films were fabricated on conductive p-Si (100) substrates with DC magnetron sputtering deposition by varying DC power applied to a Ni target. The bonding structure, surface morphology, scratch resistance and corrosion resistance of the DLC:Ni films were studied using X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, atomic force microscopy (AFM), micro-scratch test, potentiodynamic polarization test and open circuit potential measurement. The results indicated that the corrosion resistance of the DLC:Ni films in a 0.6 M NaCl solution decreased with increased Ni content in the films though the films showed good passivation behavior in the NaCl solution.     

High temperature corrosion behavior of a multilayer CrAlN coating prepared by magnetron sputtering method on a K38G alloy

A multilayer CrAlN coating of Cr_0.58Al_0.42N/Cr_0.84Al_0.16N/Cr_0.51Al_0.49N has been fabricated by a reactive magnetron sputtering method. It consists of a bonding layer, a Cr-rich intermediate layer and an Al-rich outer layer. The multilayer structure provides the coating with good protection against different types of high temperature corrosion, i.e., high temperature oxidation and hot corrosion. The outer Al-rich layer gives the coating good oxidation resistance at 1000 and 1100 °C due to the formation of a continuous alumina scale. The parabolic rate constants of the coated samples decrease by about 2 orders of magnitude compared with that of the bare alloy samples. The intermediate Cr-rich layer can form a Cr₂O₃ scale to provide good protection under the hot corrosion conditions in the Na₂SO₄ salt fluxing at 900, 950 and 1000 °C. The incubation period of the hot corrosion extends several times longer when the alloy was coated by the multilayer coating at the three selected temperatures.     

Characterization and properties of quaternary Mo-Si-C-N coatings synthesized by magnetron sputtering technique

In this paper the direct current unbalanced reactive magnetron sputtering and composite target techniques were exploited to deposit quaternary Mo-Si-C-N coatings on Si wafer and stainless steel (1Cr18Ni9) in an Ar/N₂ gaseous mixture. The chemical composition, microstructure, morphology, hardness, and friction coefficient of these films were characterized by means of X-ray diffraction, XPS, field emission scanning electron microscopy, TEM and nanoindentation. With the increase of C content in the range of C/(C + Mo + Si + N) = 0-12 at.%, the crystallite size decreases from 32 nm to 5 nm and the average friction coefficient of Mo-Si-C-N coatings decreases from 0.24 to 0.17, while the hardness increases at first and then decreases after passing a maximum value of about 27 GPa at 9 at.% C. It was suggested that in the Mo-Si-C-N coatings C atoms substitute for the N atoms in the nano-sized crystalline Mo₂N to form Mo₂N(C) solid solution phase and the microstructure of the Mo-Si-C-N coatings may be nano-sized crystalline Mo₂N(C) embedded in the amorphous SiNx and CNx phases.     

Improvement of anticorrosion and adhesion to magnesium alloy by phosphate coating formed at room temperature

A new surface protection process was developed to magnesium alloy against corrosion in aggressive environments. Firstly, a phosphate coating was formed on rinsed magnesium alloy. Then, powder painting was carried out on the phosphated magnesium alloy. Surface morphologies and phase compositions of the phosphate coating were investigated by X-ray diffraction （XRD） and scanning electron microscope （SEM）. The results show that the phosphate coatings formed in bath containing earth additives at room temperature have dense and fine microstructure. The phosphate coating provides excellent paint adhesion to the magnesium alloy. Salt spray tests indicate that the corrosion resistance of the phosphate coating plus paint could meet the demand of magnesium alloy automobile components in aggressive environments.     

Structure and optical properties of nanocrystalline NiO thin film synthesized by sol–gel spin-coating method

NiO thin film was prepared by sol–gel spin-coating method. This thin film annealed at T = 600 °C. The structure of NiO thin film was investigated by means of X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). The optical properties of the deposited film were characterized from the analysis of the experimentally recorded transmittance and reflectance data in the spectral wavelength range of 300–800 nm. The values of some important parameters of the studied films are determined, such as refractive index (n), extinction coefficient (k), optical absorption coefficient (α) and band energy gap (E_g). According to the analysis of dispersion curves, it has been found that the dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters and high-frequency dielectric constant were determined. In such work, from the transmission spectra, the dielectric constant (_∞), the third-order optical nonlinear susceptibility χ⁽³⁾, volume energy loss function (VELF) and surface energy loss function (SELF) were determined.     

Phase segregation and its effect on the adhesion of Cr-Al-N coatings on K38G alloy prepared by magnetron sputtering method

Cr_1 − xAl_xN (0 < x < 1) coatings were fabricated by a reactive magnetron sputtering method on a K38G alloy. The composition and microstructure of the coatings were investigated. Phase segregation of cubic AlN was considered in Cr_0.65Al_0.35N using X-ray diffraction analyses. This segregation of cubic AlN from CrAlN matrix might be induced by the high micro-stress. The critical failure load determined by scratch tests of the coating with c-AlN segregation was highest among all the coatings studied in the present work, which indicated that the coating has the best adhesion.     

Fatigue and corrosion fatigue behavior of an AA6063-T6 aluminum alloy coated with a WC-10Co-4Cr alloy deposited by HVOF thermal spraying

The present investigation has been conducted in order to study the fatigue and corrosion fatigue behavior of an AA6063-T6 aluminum alloy substrate coated with a WC-10Co-4Cr deposited by HVOF thermal spraying. It has been determined that the deposition of such a coating on the aluminum substrate gives rise to significant gains in fatigue life in comparison with the uncoated substrate, when testing is carried out both in air and in a 3 wt.% NaCl solution. It has been shown that during testing in air, the fatigue gain ranges between ~ 540 and 4300%, depending on the maximum alternating stress applied to the material. Larger fatigue gains are associated with low alternating stresses. Also, when fatigue testing is conducted in the NaCl solution, the gain in fatigue resistance varies between ~ 620 and 1460%. Fatigue cracks have been observed to initiate at the coating surface and then grow towards the substrate after propagating through the entire coating thickness. Crack growth along the coating has been observed to occur mainly along the regions formed by the agglomeration of W and W-Co-Cr-rich particles, flanking the tougher Co-Cr-rich areas. Although in the present work residual stresses were not measured, it is believed that the gain in fatigue life of the coating-substrate system is due to the presence of compressive residual stresses within the coating which hinder fatigue crack propagation. The deposition of the coating does not give rise to significant changes in the static mechanical properties and hardness of the aluminum alloy substrate. It has been observed that the WC-10Co-4Cr coating displays a significant indentation size effect and has a mean hardness of ~ 9.4 GPa.     

Evaluation of interfacial strength by an instrumented indentation method and its application to an actual TBC vane

The thermal fatigue behaviour of an air plasma sprayed thermal barrier coating was investigated. And also the interfacial strengths of thermal barrier coated specimens subjected to thermal fatigue, as well as a retired TBC vane were also evaluated by means of an instrumented indentation machine. The results indicated that, (1) the TGO grew at the interface during thermal fatigue cycle as a function of the exposure time at elevated temperature; (2) the microcracks were initiated in the top coating and at the...     

The structure and adhesion of hydrogenated amorphous carbon (a-C:H) films synthesized on CoCrMo alloy by plasma immersion ion implantation and deposition at different flow ratios of acetylene to argon

Hydrogenated amorphous carbon (a-C:H) film is deposited on CoCrMo alloy by plasma immersion ion implantation and deposition (PIII-D) at different flow ratios of acetylene to argon (C₂H₂/Ar). The results show that Ar fraction in the C₂H₂-Ar gas mixture has an important effect on the structure and the adhesion of the a-C:H films. When Ar fraction in the C₂H₂-Ar gas mixture is less than 50%, the fabricated a-C:H film composition transfer from graphite-like to diamond-like which contains higher sp³ binding thanks to Ar ion bombardment, and the adhesion strength decreased with the increment of Ar fraction. But when Ar fraction in the C₂H₂-Ar gas mixture is beyond 50%, the fabricated film contains more sp² bonding for thermally driven and exhibits higher adhesion strength with the increment of the Ar fraction.