Tribological behaviour of TiB2-HfC ceramic tool material under dry sliding condition

In order to disclose friction and wear mechanism of TiB₂-HfC ceramic, tribological behaviour of TiB₂-HfC ceramic sliding against YG8, 316 stainless steel (316) and TA2 were investigated. Friction coefficients between TiB₂-HfC ceramics and these materials decreased not only with an increase of sliding speed but also with an increase of normal load, respectively. Wear rates of TiB₂-HfC ceramics sliding against these materials increased with an increase of sliding speed as well as with an increase of normal load, respectively. B₂O₃, TiO₂ and HfO₂ formed in TiB₂-HfC ceramics sliding against these materials. In addition, intergranular and transgranular microcracks and WO₃ appeared in the worn surface after the ceramic slid against YG8; lamellar structures like fish scale, areas of exposed grains, pits, Fe_xO_y and Cr₂O₃ existed in the worn surface after the ceramic slid against 316; ribbon-like structures, areas of exposed grains, wear particles and furrows existed in the worn surface after the ceramic slid against TA2. Besides oxidation wear, abrasive wear played an important role in TiB₂-HfC ceramic sliding against YG8, while adhesive wear and abrasive wear played a dominant role in TiB₂-HfC ceramic sliding against 316 or TA2.     

Tribological behaviors of polytetrafluoroethylene composites under dry sliding and seawater lubrication

The composites of polytetrafluoroethylene (PTFE) filled with expanded graphite (EG), poly(p‐oxybenzoyl) (POB), and basalt fiber (BF) were prepared by heating compression and sintering molding. The tribological behavior of PTFE composites was investigated with a pin‐on‐disk tester under dry conditions and seawater lubrication. The worn surface of PTFE composites and the transfer film on the counterface were observed with a scanning electron microscope. The results indicated that the incorporation of EG and POB improved the hardness of PTFE composites, and addition of BF led to greater load‐carrying capacity. Compared to pure PTFE, the coefficients of friction of PTFE composites slightly increased, but the wear rates were significantly reduced (the wear rate of composite with 3% EG being only 10.38% of pure PTFE). In addition, all the composites exhibited a lower coefficient of friction (decreases of about 0.03–0.07) but more serious wear under seawater lubrication than under dry sliding. The wear mechanism changed from serious abrasive wear of pure PTFE to slight adhesion wear of PTFE composites under both conditions. A transfer film was obviously found on the counterface in seawater, but it was not observed under dry conditions. Among all the materials tested, the PTFE‐based composite containing 20% POB (mass fraction), 2% EG, and 3% BF exhibited the best comprehensive performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2523–2531, 2013     

Tribological properties of SiC-B4C ceramics under dry sliding condition

SiC-B₄C ceramic composites with different ratios of SiC to B₄C were produced. The relative density, mechanical properties, initial surface characteristics, dry sliding tribological properties against SiC ball and worn surface characteristics of the SiC-B₄C ceramics were studied. Results of dry sliding tribological tests showed that, 40 wt. % SiC-60 wt. % B₄C ceramic composite had the best tribological properties in SiC-B₄C ceramic composites. A relief structure with height difference of 10−30 nm between B₄C grains and SiC grains is formed after dry sliding. This relief structure, on the one hand, can reduce real contact area on interface, decreasing adhesion effect, and on the other hand, can fix or trap the wear pieces formed on sliding interface during the dry sliding process, reducing the abrasive wear. However, there is a limit to the beneficial influence of decreased adhesion effect and reduced abrasive wear, and an optimum proportion of relief structure. Pores can also fix or trap some wear pieces, reducing the abrasive wear. Under the condition of strong bonding between SiC grains and B₄C grains, the SiC-B₄C ceramic composites with higher porosity can obtain better tribological properties. In addition, it is observed by AFM that the depth of scratch on B₄C grains is shallower than that on SiC grains. Hence, it is demonstrated by micro scale measurement that the wear rate of B₄C is lower than that of SiC in this study.     

Tribological performance of DLC-coated ceramics against cemented carbide under dry sliding conditions

In order to improve the tribological behavior of Si₃N₄/TiC ceramics, DLC coating was fabricated on the ceramic surface through magnetron sputtering technology. The surface and cross-section micrographs, the adhesion between coating and substrate, the surface roughness and microhardness of the DLC-coated ceramics were investigated. Reciprocating friction tests sliding against cemented carbide ball were conducted under dry sliding conditions. The test results indicated that the DLC coating possessed superior tribological performance, which was conductive to decreasing the friction coefficient and enhancing the wear resistance of ceramics. The primary mechanisms responsible for performance improvement of the DLC-coated ceramics were attributed to the combined effects of low shear stress, excellent adhesion with substrate, high microhardness and good surface roughness. It was believed that the DLC coating was efficient in improving the load-carrying capacity and expanding the application area of ceramic materials.     

干滑动下端羟基聚丁二烯液体橡胶-环氧树脂复合材料的摩擦性能

用端异氰酸酯基聚丁二烯液体橡胶与环氧树脂制得端异氰酸酯基聚丁二烯橡胶-环氧树脂聚合物(ETPB)。在ETPB中分别加入质量分数为5%和10%的纳米三氧化二铝,并用胺类固化剂固化,制得ETPB/纳米三氧化二铝复合材料。测试了环氧树脂、ETPB和ETPB-纳米三氧化二铝复合材料在干滑动下的摩擦性能,考察了磨损率及摩擦系数与载荷和滑动速度之间的关系,用扫描电子显微镜对几种材料磨损表面进行了观察。结果表明,用端异氰酸酯基聚丁二烯液体橡胶改性环氧树脂可提高干滑动条件下环氧树脂的抗磨损性能;填充纳米三氧化二铝可显著提高ETPB的抗磨损性能,其最佳填充质量分数为5%。     

Formation of <111> fiber texture in β-SiC films deposited on Si(100) substrates

The evolution of the morphology and the texture of 3C-SiC films grown by chemical vapor deposition (CVD), using 1,3-disilabutane as precursor, on Si(100) substrates is investigated by transmission electron microscopy. Films were found to exhibit a columnar grain structure with a strong <111> fiber texture and a high density of stacking faults and twins. The columnar grains do not originate at the substrate surface but on a buffer layer about 3 to 5 nm thick, consisting of interconnected 3D-islands that initiate as epitaxial nuclei. The change from <100> epitaxial islands to <111> columnar grains can be understood in terms of anisotropic growth rates and multiple twinning. The observed <111> fiber texture, faulted substructure, faceted surface morphology and carbon enrichment of the growth surface are in agreement with the proposed growth model.     

Tribological investigation of nanocrystalline diamond films at low load under different tribosystems

The mechanical and frictional properties of hydrogen- and oxygen-terminated nanocrystalline diamond films (NCD) grown by hot-filament chemical vapor deposition (HFCVD) have been investigated in the present work.The structure and morphology of the NCD films have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman-effect spectroscopy. In addition, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) have been used to investigate the surface chemical groups on the NCD surface. Mechanical and frictional properties are determined using atomic force microscopy (AFM), nano-indentation, nano-scratching and micro-tribometer. The friction behavior of these films in the load range of 25 to 200 mN under reciprocating sliding conditions, using steel counter-body material has been thoroughly studied.It is noted that these films are highly crystalline with nanometer size grains and contain a very high fraction of sp³ carbon bonds. They exhibit high hardness and high elastic modulus. The friction coefficient of the film is lower under unidirectional scratch with diamond indenter than the friction coefficient under low load reciprocating sliding against steel ball. Transfer of the film from the counter-body, oxidation of transfer film and mixing of transfer film with carbonaceous layer on the worn surfaces are responsible for such behavior. Although, the friction responses of H-terminated and O-terminated films are similar under unidirectional scratch with diamond indenter, the friction coefficient of O-terminated film is always higher than the friction coefficient of H-terminated film under reciprocating sliding condition against steel counter-body material.     

Tribological behavior of the polyamide composite coating filled with different fillers under dry sliding

The polyamide (PA) composite coating filled with the particles of microsized MoS₂, microsized graphite, and nano‐Al₂O₃, respectively, were prepared by flame spraying. The friction and wear characteristics of the PA coating and composite coating filled with the varied content of filler under dry sliding against stainless steel were comparatively investigated using a block‐ring tester. The morphologies of the worn surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. The result showed that the addition of fillers to the composite coatings changed significantly the friction coefficient and wear rate of the coatings. The composite coatings filled with a low level content of fillers showed lower wear rate than did pure PA coating under dry sliding; especially the MoS₂/PA composite coating had the lowest wear rate among these composite coatings. The composite coatings with a high level content of fillers had higher wear rate than did pure PA coating, except of the Al₂O₃/PA composite coating. The bonding strengths between the polymer matrix and fillers changed with the content of the fillers, which accounted for the differences in the tribological properties of the composite coatings filled with the varied content fillers. On the other hand, the difference in the friction and wear behaviors of the composite coatings and pure coating were attributed to the difference in their worn surface morphologies and transfer film characteristics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Incorporation of lithium and nitrogen into CVD diamond thin films

High concentrations of lithium (~ 5 × 10¹⁹ cm^− 3) and nitrogen (~ 3 × 10²⁰ cm^− 3) have been simultaneously incorporated into single-crystal and microcrystalline diamond films using Li₃N and gaseous ammonia as the sources of Li and N, respectively. Using sequential deposition methods, well-defined localised layers of Li:N-doped diamond with a depth spread of less than ± 200 nm have been created within the diamond. The variation in Li:N content and amount of diffusion within the various types of diamond suggests a model whereby these atoms can migrate readily through the grain-boundary network, but do not migrate much within the grains themselves where the diffusion rate is much slower. However, the high electrical resistivity of the doped films, despite the high Li and N concentrations, suggests that much of the Li and N are trapped as electrically inactive species.     

Tribological behaviour of Ti containing nanocomposite DLC films under milli-Newton load range

In recent days nanocomposite films deposited by various CVD or PVD techniques are receiving intense attention because of their high hardness or high toughness. These films are considered to be potential layers for tribological applications. The present investigation is undertaken to evaluate the tribological behaviour of a nanocomposite Ti containing diamond like carbon film in the load range of milli-Newtons keeping in view the possible application in micro mechanical assemblies (MMA). Towards that purpose, films containing various Ti concentrations are deposited with the help of unbalanced magnetron sputter deposition technique. The tribological properties of these films are evaluated at 500 mN applied load. It is noted that the film containing 46 at % Ti has the maximum hardness in the order of 15.5 GPa and also very high plastic deformation. This film also shows a very low friction coefficient and wear rate.     

Durability and degradation mechanism of graphene coatings deposited on Cu substrates under dry contact sliding

The durability and degradation mechanism of graphene coatings deposited on Cu substrates under dry contact sliding were assessed. The motivation was to develop an ultra-thin protective coating for precision components based on the excellent mechanical properties of graphene. The graphene coatings were deposited on polycrystalline Cu substrates by chemical vapor deposition at atmospheric pressure. The uniformity and quality of the coating could be improved by increasing the growth time from 5 to 20 min. This also led to increase in the durability of the coating which was determined by noting the point of drastic increase in friction. Eventual degradation of the graphene coating with increasing number of sliding cycles could be characterized by the transformation of graphene to amorphous carbon. Nevertheless, the ability of ultra-thin graphene coating in protecting the surface of metal under dry contact sliding was clearly demonstrated at the macro-scale.     

Electrical properties of thick boron and nitrogen contained CVD diamond films

The acceptor and donor defects of thick (approx. 0.4 mm) free-standing boron and nitrogen containing microwave plasma CVD polycrystalline diamond films were investigated. Charge-based deep level transient spectroscopy (Q-DLTS) was applied to study impurity-induced defects, their density and energy distribution in the energy range of 0.01 eV≤E−E_v≤1.1 eV above the valence band. It was shown, that differential capacitance–voltage, and Hall effect measurements combined with DLTS data can be used to determine the degree of compensation, and the concentration of compensating donors (mostly the positively charged single-substitutional nitrogen (N⁺)) in p-type CVD polycrystalline diamond films. It was found, that incorporated boron atoms induce three levels of electrically active defects. Two of them with concentration (2–3)×10¹⁶ cm⁻³ each have activation energies of 0.36 and 0.25 eV with capture cross-sections of 1.3×10⁻¹³ and 4.5×10⁻¹⁹ cm², respectively. The third type of defect has an activation energy of 0.02 eV, capture cross-section 3×10⁻²⁰ cm² and concentration 10¹⁵ cm⁻³, this shallow trap being a probable general caterer of holes in low-doped films. The total concentration of electrically active uncompensated acceptors in all p-type diamond samples was approximately 2×10¹⁷ cm⁻³ with hole concentration of approximately 1.5×10¹⁴ cm⁻³ and hole mobility in the range of 30–40 cm² V⁻¹ s⁻¹ at room temperature. If assumed that compensating donors are mostly nitrogen, the films contained no less than 3×10¹⁶ cm⁻³ of N⁺.     

Deep ultra-violet Raman imaging of CVD boron-doped and non-doped diamond films

Deep UV (244 nm) Raman images were recorded on CVD diamond films. The different images recorded on boron-doped polycrystalline film reveal large differences on the boron level within individual crystallites. Nevertheless, inspite of an enhanced intensity of the diamond line, the UV Raman spectra are less informative than the visible Raman spectra due to the weak response of the boron-related peaks. The images recorded on an un-doped homoepitaxial diamond film reveal a defective domain exhibiting in the same areas the sp³ CH_x stretching vibration component and the first and second-order optical phonons of the graphite-like phonon bands of sp² carbons embedded in a compressive zone of polycrystalline diamond.     

Bulk photoconductivity of CVD diamond films for UV and XUV detection

Owing to its semiconducting properties (wide band gap, high electron and hole mobility), diamond is an interesting material for UV and XUV photodetection. In the present study, we have characterized UV and evaluated XUV diamond photodetector efficiency using volume photoconductivity instead of usual surface interdigited devices. The detectors have been tested under over-gap (13 and 193 nm) as well as sub-gap nanosecond laser irradiation (266 nm). For each wavelength, electrical characteristics of the devices have been measured as a function of bias voltage and laser fluences. The particular sandwich configuration of the detectors has shown a charge effect under over-gap irradiation. This appears by the amplitude reduction of successive pulses, and also from the different response for AC and DC bias. The suitability of these devices is discussed, the final aim being to validate bulk structures for wide band imaging devices.     

High quality textured growth of oriented diamond thin films on Si (100) in a hot filament-CVD system

High quality textured and oriented diamond (100) films were grown in a two step process on Si (100). Bias-enhanced nucleation and textured growth by microwave CVD was followed by hot filament deposition without the addition of nitrogen to yield a smooth (100) oriented surface with defect free (as judged by SEM) areas of up to 200×200 μm² and no detectable (111) facets. Low energy electron diffraction confirmed the high degree of lateral ordering which is much improved compared with oriented textured diamond grown by conventional methods on Si (100). Raman measurements confirm the excellent quality of these films with no detectable graphitic or amorphous carbon phase and a vanishing background due to nitrogen related photoluminescence.     

Characterization of phosphorus doped CVD diamond films by cathodoluminescence spectroscopy and topography

A phosphorus doped homoepitaxial diamond film made by a CVD method was investigated by cathodoluminescence spectroscopy and topography. An exciton peak bound to phosphorus at 239 nm was observed from {001} as well as {111}, but the wavelength and width of the peak varied depending on location of the sample. This may be due to the difference of crystal perfection. It was found in the spectra that the slope with an array of weak peaks has a maximum of approximately 270 nm. This broad band may be an indicator of incorporation of phosphorus, although all the phosphorus doped diamonds do not exhibit the band. No other peak expected to be related to phosphorus was found, but several peaks commonly observed from CVD diamond were seen instead. These were also dependent on growth surface. Peaks at 415, 482, 500, 514 and 532 nm were strong on {111} surfaces of the non-epitaxial crystallites, whereas the 575-nm peak and another system of the 532-nm peaks were stronger in {001} epitaxial layers, as reported earlier.     

Electrical properties and defect analysis of neutron irradiated undoped CVD diamond films

High-quality detector-grade CVD diamond films have been irradiated with fast neutrons up to 2×10¹⁵ n/cm² (1 MeV neutron-equivalent). Thermally stimulated currents (TSC) and thermoluminescence (TL) analysis have been performed. After irradiation, a decrease in the TSC and TL signal intensity is observed, while no significant changes in the spectrum shape are found. The TSC analyses have been performed as a function of the electric field and the results have been discussed in terms of the Poole–Frenkel effect.     

Patterning of CVD diamond films by seeding and their field emission properties

Selective seeding for growing diamond on Si substrates was performed by conventional lithography using photoresist mixed with fine diamond particles. The selectivity was improved by filtering the diamond powder-photoresist mixture and carrying out reactive ion etching of patterned substrates. As a result, a selectivity up to 2.0 × 10² or higher was achieved. The resolution was of the order of 1 μm. Field emission from diamonds prepared using this selective growth method was observed without any postgrowth treatment. The measured current vs. voltage plot of a diode showed a rectifying characteristic. Under a forward bias, a current of about 15 μA was obtained at about 570 V, with a turn-on voltage of about 480 V. The emission current was comparable with that which had been observed for Si field emitter tips.