ICMCTF2015 Session EP: Symposium E Poster Session

The main objective of this work has been the deposition of hybrid Cu/WC/Graphene nanocomposites and characterization their tribological behavior. Graphene as a conductive solid lubricant additive were introduced into Cu matrix from the electrolytes in which submicron WC particles and graphene nanosheets were suspended. The main purpose for two different reinforcement co-deposition process is to improve the tribological properties while maintaining good electrical conductivity. The amount of reinforcements was changed in the Cu matrix to optimize the best electrical conductivity and tribological properties. The friction and wear behaviors of Cu/WC/Graphene coatings on the metal substrates against Al₂O₃ ball were tested under dry sliding wear conditions. Comprehensive characterizations were performed using Environmental Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction analysis and 3D profilometry facilities. Tribological test results have revealed that small amounts of Graphene addition are able to drastically improve the antifriction and antiwear properties of hybrid nano Cu matrix composites. A possible explanation for these results is that, the co-deposition of graphene not only provide an enhanced effect for nanocomposites to produce better wear resistance, but also form a local protective layer on the contact surfaces to reduce the friction. The investigation shows that hybrid reinforcements of sub-micron WC and graphene hold great potential applications as an effective solid lubricant for Cu matrix composites and possibly other alloys.

Keywords: Electrophoretic co-deposition, sub-micron WC, electrical contact, graphene nanosheets, sliding friction, solid lubrication, wear mechanisms

This communication focuses on the structural and mechanical properties of binary Zr_xCu_1-x (ZC) glassy alloy deposited by rf magnetron (co-)sputtering on silicon substrates. Mechanical properties of films will be investigated versus deposition parameters, thickness and as a function of temperature. Obviously, as mechanical properties are directly related to the structure to the thin films they should exhibit differences when it changes from amorphous to partially or totally crystalline. We use two techniques to characterize the mechanical properties : (i) The Brillouin light scattering (BLS) for sound velocities and isotropic elastic properties C_ij at room temperature or as a function of temperature; (ii)Room temperature RT nanoindentation for E and H, and direct comparison to the existing data in literature as to BLS.

In order to in-situ study the effect of the temperature on the elastic constants, The Brillouin light scattering (BLS) has been recently combined with a high-temperature chamber dedicated to optical techniques; samples can be heated up to 1600°C, in air or under controllable vacuum (pressure down to 5.10^-7 Pa). In this talk, we will show results on Zr_0.5Cu_0.5 and discuss the links between structure, mechanical properties and their evolution during temperature annealing.

It is known that AISI 4340 alloy steel has been widely applied in landing gears. This study separately utilized the three films, TiN, TiAlN, and TiN/TiAlN, to coat the material through cathodic arc deposition technology. Coating morphology and structure were analyzed by using FESEM, XRD, and TEM. Moreover, Rockwell-C indentation, nanoindention, ball-on-disk wear tests, and polarization tests were all performed to explore the coating properties such as adhesion, hardness, elastic modulus, wear resistance, and corrosion resistance, respectively.

TiNi shape memory thin films have been widely applied in the fields of biomedical and microelectromechanical systems for their unique superelastic properties and shape memory effects/behaviour. The micro-abrasion wear test is known to be a useful tool for evaluating the wear resistance of the ceramic thin films, such as TiN and TiAlN. However, few studies have been done to understand the micro-abrasion wear behaviour of TiNi metallic thin films. There are especially interests because their distinct material properties such as micro-twinning and (reversible) martensitic transformation.

The treatment of surfaces is one of the main factors to control the adhesion between coating and substrate on a cutting tool. Poor coating adhesion on the tool accelerates the wear and decreases the tool life due to the fragmentation and release of hard abrasive particles between the tool and the workpiece. Mechanical and chemical substrate pre-treatments are applied to optimize the coating adhesion. This work evaluated and compared the effectiveness of chemical polish and magnetron sputtering techniques in the improvement of substrate-coating adhesion, and consequently the tool life of PVD coated cemented carbide tools. The sputtering was performed in plasma reactors which the cations produced collide with the samples and remove surface atoms or molecules modifying the topography. In the chemical polishing, it was used acid and alkaline solutions to remove tool surface material, changing its initial roughness and chemical composition. After these surface treatments, the samples were PVD coated with TiNAl. To ascertain the effectiveness of surface treatment, Rockwell C indentation and turning experiments were performed on treated tools and conventional untreated tools. The tool topography was analyzed by atomic force microscopy (AFM) and the wear was evaluated by scanning electronic microscopy (SEM). The tool with sputtering treatment showed better performance in the indentation and turning tests than other tools. Therefore, the tool treated with chemical polish showed the highest roughness, but the coating adhesion was poor due to chemical changes in substrate surface. The good anchoring is not influenced only by the highest roughness but depends on chemical nature of substrate surface.

Hard transparent coatings are of utmost importance in applications where surface protection should be achieved without influencing the visual appearance of substrates. Acrylates are often used as they can allow high hardness and ensure adhesion on several underlying substrates like plastics, glass and metals. In this work, radiation curable acrylate coatings based on Trimethylol Propane Triacrylate (TMPTA) monomers and deposited on thermoplastic polycarbonates by spraying was compared with two nano-composite systems. The former system is formulated by shear mixing of colloidal nano-silica dispersed in reactive TMPTA monomers with additional diluted TMPTA. The latter is formulated by mechanical dispersing colloidal nano-silica in diluted TMPTA. Progressive and constant load scratch tests with a Rockwell C indenter and an ASTM/ISO standard-based scratch machine were used to evaluate the micro-mechanical performance of the investigated coatings. Dry sliding tribological tests were used to evaluate the wear endurance of the coatings. Colloidal nano-silica dispersed in TMPTA was found to significantly enhance the micro-mechanical response and wear resistance of the acrylate coatings. They also gave rise to highly transparent and adherent coatings on polycarbonates, whilst leaving their visual appearance virtually unchanged.

Polysiloxane coatings are widely used as protective barriers to delay erosion/corrosion and increase chemical inertness of metal substrates. Although highly performing, polysiloxane resins are always designed through a firm control of the molecular weights during synthesis and an appropriate selection of the side groups, as the expected mechanical performance is strictly dependent on them. In addition, an accurate control of the coating process is compulsory if the establishment of good barriers with low porosity and high adhesion to the substrate is the awaited goal. In the present work, a high molecular weight methyl phenyl polysiloxane resin was designed to manufacture a protective coating for Fe 430 B structural steel. Methyl groups feature a very small steric hindrance and confer ductility to the Si-O-Si backbone of the organic inorganic hybrid resin, thus allowing the achievement of fairly high coating thickness. Phenyl groups feature a larger steric hindrance, but they ensure stability and high chemical inertness. The resulting resins yielded to protective coatings which feature a remarkable adhesion to the substrate, good scratch resistance and high wear endurance, thus laying the foundations to manufacture long lasting protective barriers against corrosion and, more in general, against aggressive chemicals.

Friction in rotating components is of utmost importance in several applications, as it influences significantly abrasive contact and, consequently, wear endurance of adjoining substrates. Friction is known to be strongly correlated to surface morphology and, in specific, to surface roughness. In the present work, an analysis involving multi-scale decomposition of surface morphology and prediction of friction coefficient was developed. This approach is applied to the investigation of the influence of the finish scale of annular brass workpiece after abrasive fluidized bed finishing on the friction coefficient. In particular, the resulted surface morphologies of the workpiece after finishing under different processing conditions were decomposed in different roughness scale by multi-scale decomposition based on ridgelets transform. The resulting data were the inputs to a model designed to predict the effect of the roughness scales on the contact dynamics. The results allow relating the influence of the different finish scales on the friction coefficient for a variety of tribological scenarios.

Diamond-like carbon (DLC) and carbon-nitride (CN_x) coatings deposited on steel machine components are of industrial interest for tribological applications due to potential reduction in friction, wear and corrosion. In this paper we compare the mechanical, macro- and nano-tribological properties, and corrosion behavior of DLC films deposited by PACVD and CN_x films deposited by magnetron sputtering.

The substrates were heat-treated AISI-420 SS-discs. DLC coatings were deposited by PACVD using acetylene precursor at T_S=150ºC for 2h, obtaining films of ~2.5 µm-thick, with an adhesive a-Si interlayer. CN_x films were deposited using MF magnetron-sputtering in a mixture of Ar/N₂ at T_S=150 ºC and 100V bias for 6 h using an industrial CemeCon CC800/9-ML system, resulting films of ~1 µm-thick, with an adhesive Cr interlayer.

The coating microstructure and composition were analyzed by SEM, XPS and Raman. Adhesion was evaluated by Rockwell-C indentations and Scratch Test. The macrotribological properties were evaluated by pin-on-disk tests with alumina balls, while the nanomechanical and nanotribological properties were measured by a Triboindenter-TI950 with a conical diamond tip. Salt spray tests (ASTM-B117) and electrochemical experiments were conducted in order to evaluate the corrosion behavior.

A remarkable improvement of tribological properties of pure titanium was achieved by developing multilayer treatment method in this study. The pure titanium specimens were conducted to the duplex surface treatment. In the first treatment, plasma nitriding treatment was performed at 600 °C and 700 °C for 4 hours on the pure titanium specimens. In the second treatment, the nitrided specimens were coated with CrN by physical vapor deposition (PVD). The friction and wear properties of the duplex treated specimens were investigated for tribological applications. Surface morphology and microstructure of the duplex treated specimens were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, tribological properties were investigated using pin-on-disc tribometer. It was observed that the wear resistance values of treated specimens were higher than the untreated pure titanium values.

Ternary carbides coatings like NbVC2 were deposited by means of thermo-reactive deposition/diffusion technique onto AISI D2 steel substrates used in the fabrication of several tools. In order to obtain these coatings a mixture of sales molten borax bath (Na2B4O7.5H2O), carbide forming elements such as vanadium and niobium and a reducing agent as aluminum at 81%, 8% and 3% respectively. This mixture was made inside a stainless steel cresol and the whole system was carried until 1293K during 4 hours.

Regarding to the characterization of the coatings the mean thickness was about 6um. The presence of the phase NbVC₂ was evaluated by means of X-ray diffraction analysis. The behavior against erosion-corrosion of the coatings was valued through potentiodynamic polarization curves and the measurement of the loss of weight according to the procedure in the ASTM G119-09. The angle of the impact was set at 30° and 90° and velocity of impact of 9,5 m/s and 11,5 m/s. Results shown that the total rate of waste can be reduced above 60% respect to the substrate with this kind of coating. A strong reduction of the synergistic effect was manifested and this was shown by the reduction of the pure erosion effect for velocities 9,5 m/s and 11,5 m/s in 90° and 30°, and a reduction in the pure corrosion effect was shown too. The major contribution of the synergistic effect was presented in the blank steel for the 90 degrees angle y velocity of 11,5 m/s. For all the conditions erosion was the main mechanism of wear.

Damage evolution of electron beam-physical vapor deposited (EBVD-PVD) ZrO₂-7 wt.% Y₂O₃ thermal barrier coatings (TBCs) under thermal cyclic conditions was monitored using an acoustic emission (AE) technique. The coatings were heated using a laser heat flux technique that yields a high reproducibility in thermal loading. Along with AE, real-time thermal conductivity measurements were also taken using infrared thermography. Tests were performed on samples with induced stress concentrations, as well as calcium-magnesium-alumino-silicate (CMAS) exposure, for comparison of damage mechanisms and AE response to the baseline (as-produced) coating. Analysis of acoustic waveforms was used to investigate damage development by comparing when events occurred, AE event frequency, energy content and location. The test results have shown that AE accumulation correlates well with thermal conductivity changes and that AE waveform analysis could be a valuable tool for monitoring coating degradation and provide insight on specific damage mechanisms.