Investigation of mechanical and tribological properties of amorphous diamond-like carbon coatings

We investigated the mechanical and tribological properties of amorphous diamond-like carbon (DLC) coatings deposited on Si(100) by a pulsed bias deposition technique. Tribological studies were performed using a pin-on-disc (POD) apparatus under a normal load of 6.25 N and at 10% relative humidity, with a ruby pin as a slider. Hardness measurements were performed using a nanoindenter and apparent fracture toughness using indentation techniques. We studied the influence of residual stresses on apparent fracture toughness. The data revealed that the thickness, hardness and compressive stress of the coating play different roles in the apparent fracture toughness. Crack initiation is influenced by the thickness and hardness of the coating, whereas crack propagation is influenced by the compressive stress in the film. The apparent fracture toughness of DLC coatings increased with coating hardness.     

Combined influences of mechanical properties and surface roughness on the tribological properties of amorphous carbon coatings

Carbon films (∼2 μm thick) with a range of mechanical properties and underlying substrate roughnesses were evaluated for delamination and wear under conditions of combined impact and sliding contact. One-side-coated and both-sides-coated titanium alloy pin and disk wear couples were assessed using a custom-made impact/sliding pin-on-disk apparatus in a colloid-based blood volume expansion medium. The normal stress distribution along the film/substrate interface upon impact loading by a smooth titanium alloy pin was modelled analytically for each coated system. For disk surface roughness centre-line average (R_a) values below 0.05 μm, the area of disk film delamination was shown to correlate with the presence of tensile stress at the film/substrate interface. The interfacial tensile stress was shown to occur when there was a film/substrate elastic modulus mismatch, either within or outside the perimeter of contact, depending on the direction of the film modulus deviation. We propose that the tensile stress promotes delamination by lifting the film locally from the substrate. With increased disk R_a, the area of disk coating loss tended to decrease, because the surface roughness improved the mechanical bonding of the composite system.     

The influence of surface defects on the mechanical and tribological properties of VN-based arc-evaporated coatings

The influence of surface defects, i.e., droplets and craters, on the mechanical and tribological properties of arc-evaporated V_xN coatings deposited on cemented carbide has been investigated in a scratching contact using a diamond stylus and a sliding contact using a stainless steel pin. Post-test characterisation using 3D optical surface profilometry and scanning electron microscopy was performed in order to investigate the mechanical and tribological response of the coatings. The results show that scratch induced coating cracking mainly is restricted to larger droplets showing a low interfacial bonding to the adjacent coating matrix. The influence of coating defects on the cohesive strength, i.e., the tendency to chipping of small coating fragments, was found to be relatively small. In contrast, the presence of defects may have a significant impact on the interfacial adhesive strength, increasing the tendency to spalling. In sliding contact, surface defects such as droplets and craters have a strong impact on the tribological behaviour of the coatings causing abrasive wear of the less hard counter material surface and material transfer to the coating, both mechanisms affecting the friction characteristics of sliding contact tribo systems.     

Mechanical and tribological properties of short-fiber-reinforced SiC composites

The short-carbon-fiber-reinforced SiC (C_sf/SiC) composites were prepared by hot-pressing sintering with Si, Al and B as sintering additives. The effects of fiber volume fraction on the mechanical and tribological properties of the C_sf/SiC composites were investigated. The results show that the bending strength values of the composites containing a certain content of the short carbon fibers are higher than that of the monolithic SiC. The friction coefficients of the composites decrease with increasing short carbon fibers content. Except of the composite containing 53 vol% short carbon fibers, the wear rates of the composites decrease with increasing short carbon fibers content, and are lower than that of the monolithic SiC drastically.     

Dependence of mechanical and tribological properties of diamond-like carbon coatings on laser deposition conditions and alloying by metals

The paper deals with the study of the effect of the intensity of the pulse laser irradiation of a graphite target (the fluence) on the rate of deposition, density, and the mechanical and tribological properties of diamond-like carbon coatings formed on a steel substrate at room temperature. The diminishing of the fluence from 50 to 5 MW/mm² yields a substantial (more than by an order of magnitude) increase in the coating deposition rate. However, these coatings have the lowered mechanical and tribological properties. The possibility of enhancing the coating characteristics by additional alloying with such metals as W and Ti in concentrations of up to ??10 at % is studied. The type of the metal and its distribution in the coating depth affect greatly the coating surfaces. The most stable combination of good antiwear and antifriction characteristics of the friction pair is reached after bulk alloying with tungsten.     

Nanostructural wear-resistant coatings produced on metal-cutting tools by electric-arc evaporation and magnetronic sputtering

The structure and properties of TiN, Ti-Si-N, Ti-Al-Si-N, Ti-Cr-Si-N, Ti-Zr-Si-N, Ti-B-N, Ti-Cr-B-N, and Ti-Si-B-N coatings obtained by reactive electric-arc evaporation and magnetronic sputtering of Ti, TiSi, TiAl, TiCr, TiZr, TiBN, TiCrB, and TiSiB targets are compared. Tests of cutting tools with these coatings in the drilling, turning and milling of steel indicate that the coating increases the tool’s life by a factor of 5–20.     

Mechanical and unlubricated tribological properties of titanium-containing diamond-like carbon coatings

Titanium-containing diamond-like carbon (Ti-DLC) coatings were deposited on steel with a close-field unbalanced magnetron sputtering in a mixed argon/acetylene atmosphere. The morphology and structure of Ti-DLC coatings were investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Nanoindentation, nanoscratch and unlubricated wear tests were carried out to evaluate the hardness, adhesive and tribological properties of Ti-DLC coatings. Electron microscopic observations demonstrated the presence of titanium-rich nanoscale regions surrounded by amorphous carbon structures in Ti-DLC coating. The Ti-DLC coatings exhibit friction coefficients of 0.12–0.25 and wear rates of 1.82 × 10^?9 to 4.29 × 10^?8 mm³/Nm, depending on the counterfaces, sliding speed and temperature. The Ti-DLC/alumina tribo-pair shows a lower friction coefficient than the Ti-DLC/steel tribo-pair under the identical wear conditions. Increasing the test temperature from room temperature to 200 °C reduces the coefficient of friction and, however, clearly increases the wear rate of Ti-DLC coatings. Different wear mechanisms, such as surface polishing, delamination and tribo-chemical reactions, were found in the tribo-contact areas, depending on different wear conditions.     

Tribofilm formation and tribological properties of TiC and nanocomposite TiAlC coatings

In a recent work a concept for self lubricating low friction TiC and nanocomposite TiAlC coatings was developed. Here we further investigate the mechanical and tribological properties of these coatings. Under identical deposition conditions, the addition of Al initiates the formation of a nanocomposite consisting of (Ti,Al)C grains in an amorphous carbon matrix. The coefficient of friction is lowered from ～0.2 to below 0.1 in a pin-on-disc test against steel with unaffected coating wear rate. The lower friction is attributed to a more extensive formation of amorphous carbon and graphitisation on both the counter surface and in the coating wear track. The addition of Al also reduces coating hardness, Young's modulus and the residual stress, which can be explained by the weak carbide-forming ability of Al and the formation of a nanocomposite microstructure.     

Evaluation of wear and tribological properties of coatings rubbing against copper

A new crossed-cylinders tribo-tester is proposed. This tribo-tester can decrease the tendency of the chatter vibration. The tribological properties of coatings against copper is evaluated with this tribo-tester. The wear rate of TiN, TiC and TiCN rubbing against copper is higher than the substrate high speed tool steel: SKH51 (JIS). The catalytic action of copper for oxidation of Ti-based coatings is a main reason of this high wear rate of TiN, TiC and TiCN rubbing against copper. The wear rate of CrN rubbing against copper is in a very low level because CrN shows the excellent oxidation resistance and Cr₂O₃ film formation decreases the wear loss of CrN coating.     

Mechanical and tribological properties of nanostructured coatings based on multicomponent oxides

The mechanical and tribological properties of thin (up to 300 nm) oxide coatings that are produced by the carboxylate method and have various chemical compositions and thicknesses and are deposited on substrates from different materials (steel or quartz glass) have been assessed. The study involves the surface examination and the determination of the surface roughness of specimens using optical and atomic force microscopes, the determination of the elastic properties of the coatings based on indentation results, as well as the study of their tribological behavior during dry and lubricated sliding.     

Deformation and mechanical properties of components produced by plastic shaping

The deformation and mechanical properties of components obtained by cold stamping may be analyzed by determining the scalar hardness field over the volume of the plastically deformed material. This permits the prediction of the components’ performance.     

Effect of vacuum annealing on tribological behavior of nanosized diamond-like carbon coatings produced by pulse vacuum-arc method

Results of tribotests of nanosized carbon coatings formed on silicon surfaces by the pulse vacuum-arc method at various orientations of substrates with regard to a carbon plasma flow are presented; the tribotests were carried out for as-deposited coatings and coatings annealed in vacuum at 600 and 800°C. It has been shown that, among as-deposited coatings, the carbon coating deposited on a substrate perpendicular to the axis of the plasma flow has the highest wear resistance. An increase in the wear resistance of diamond-like carbon coatings after annealing at 600°C has been found.     

MoS2-Zr复合薄膜的结构及摩擦特性研究

采用中频磁控溅射技术及多弧离子镀相结合的复合镀膜工艺,在硬质合金YT14基体上制备了MoS2-Zr复合薄膜.观察了MoS2-Zr复合薄膜表面及截面形貌,测试薄膜的厚度、结合力和显微硬度,进行摩擦磨损试验,并分析薄膜的摩擦磨损机理.结果表明,制备的MoS2-Zr复合薄膜结构致密,性能明显优于MoS2薄膜;厚度由2.0μm提高到2.5μm,结合力由28N提高到60N,显微硬度由280HV提高到900HV.MoS2-Zr复合薄膜的摩擦特性明显优于MoS2薄膜.MoS2薄膜磨损初始阶段摩擦因数只有0.06,在磨程15m后摩擦因数升到0.4.而MoS2-Zr复合薄膜的摩擦因数磨损初始阶段可达0.08,直到磨程60m摩擦因数达到0.4.薄膜的摩擦磨损过程主要是薄膜的剥落和转移的过程,复合薄膜由于结合力和硬度的提高,能够延缓薄膜的剥落及转移,提高薄膜的摩擦特性,延长薄膜的减摩润滑时间.     

Structural and mechanical properties of (Cr,Ni) N single and gradient layer coatings deposited on mild steel by magnetron sputtering

Ternary single and gradient layer (Cr, Ni) N thin films were deposited on the mild steel substrate by unbalanced magnetron sputtering technique in order to evaluate mechanical properties for machine tools and automotive applications. Microstructure, chemical composition, surface morphology and phase analysis were carried out using field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction, respectively. Both single and gradient layer of (Cr, Ni) N coatings show a significant increment in mechanical properties such as hardness, adhesion strength and surface roughness along with the reduction of friction coefficient. Mechanical tests revealed that the hardness of the gradient layer increased up to 3.1 times due to the formation of Cr₂N and Ni phase whereas single layer showed the least friction. Single layer CrNiN layer exhibited 27.2% less surface roughness (R_a) in comparison with gradient layer. High values of surface roughness, hardness, thickness and friction could be correlated with high film-to-substrate adhesion (L_c2) for the gradient layer.     

Tribotechnical and mechanical properties of Ti-Al-N nanocomposite coatings deposited by the ion-plasma method

The possibility of formation of nanocrystalline Ti-Al-N coatings using the method of ion-plasma deposition is demonstrated. The mechanical and tribotechnical characteristics of the coatings in comparison with TiN coating are studied. Ti-Al-N nanocomposite coatings possess high hardness (35 GPa) and higher wear resistance and lower wear capacity as compared to TiN coating. For a grain size of 12–15 nm the nanostructural Ti-Al-N coating has the following elemental composition: Ti ≈ 60 at %, N ≈ 30 at %, Al ≈ 10 at %. The phase composition of the coating represents the solid solution (Ti, Al)N. For this elemental and phase composition and nanograin size maximal hardness and elasticity modulus of the coating are found.     

Preliminary studies of the influence of cryo‐treatment on the mechanical and tribological properties of ptfe and composites

Cryogenic treatment of polytetrafluoroethylene (PTFE) has proved beneficial in improving the abrasive wear resistance of several polymers, and it was thus assessed in an adhesive wear mode, as well. Preliminary investigations on the effect of cryogenic treatment on the tribological properties, in adhesive wear mode, and mechanical properties of neat PTFE and it composites filled with bronze or short glass fibres (GF) were carried out. It was found that, although the improvement in the wear and friction performance of neat PTFE and a GF + PTFE composite was significant, no such positive effect was observed for the bronze + PTFE composite. On the contrary, this composite showed a deterioration in performance. The reason behind the improvement in the tribological behaviour of neat PTFE and the GF + PTFE composite could not be clearly understood. However, it was confirmed that, if the treatment adversely affected the mechanical properties, then the tribological performance also deteriorated. An examination of the worn surface of the material and the counterface disc using a scanning electron microscope revealed changes in the microstructure due to the treatment. It was also confirmed from these SEM studies that the compatibility of bronze and PTFE was very poor, which led to poor performance of the composite both in the untreated and the cryo‐treated form. Further detailed investigation and analysis of various materials and composites, however, are necessary to establish the utility of this technique.     

Investigation of the tribological properties of the different textured DLC coatings under reciprocating lubricated conditions

In this study, we propose the use of laser surface texturing methods to improve the wear resistance of diamond-like-carbon (DLC) coatings. First, the application of dimples perpendicular to an engineering surface is introduced by using laser in a controlled manner. The solid DLC lubricant is subsequently deposited on the textured surface using the magnetron sputtering technique. In the experiments, the dimple densities were varied from 0 to 30%, and the dimple diameters were varied from 40 to 300 μm. The effect of the geometric parameters on the wear performance was studied using a reciprocating sliding-wear tester under oil lubrication conditions. The results showed that the DLC coatings with the appropriate dimple density (10%) and diameter (∼100 μm) demonstrated an obvious improvement in terms of the friction coefficient and wear rate compared with that of the un-textured DLC coatings. The experimental treatment produced respective reductions of 20% in friction and nearly 52% reduction of wear rate. This improvement could be explained by the action of reservoirs that enhance lubricant retention and trap the wear particles during sliding motions. In addition, the relationship between the dimple diameter, the contact width ratio and the wear performance is discussed.     

Investigation of mechanical and tribological properties of tribo‐layer of Ni3Al matrix composites

The sliding wear of Ni₃Al matrix composites with addition of 1.5 wt.% graphene nanoplates was studied through pin‐on‐disc wear testing. The spontaneous formation of a tribo‐layer produced during sliding wear was found to result in a deviation from Archard scaling and an unexpected high wear resistance that was not based on hardness alone. The tribo‐layer exhibited specific microstructural evolution with significant severe deformation and grain refinement after wear. In the grain refinement area, the accumulation of dislocations and an increase in misorientations were found to lead to strain hardening. For the plastic deformed area, reduction in the dislocation density inside the elongated ultrafine grains reduced strain hardening compared with the grain refinement area. It can be concluded that the deviation from Archard scaling occurred primarily as a result of the microstructural evolution of the tribo‐layer, resulting in the specific performance of mechanical and tribological properties of Ni₃Al matrix composites under cyclic sliding wear process. Copyright © 2016 John Wiley & Sons, Ltd.     

Microstructure,tribological and mechanical strengthening effect of multiphase Zn/ZrO<Subscript>2</Subscript>-SiC electrodeposited composite coatings

In an attempt to improve the mechanical and thermal resilient properties of mild steel, Zn-ZrO₂-SiC composite coating was fabricated from zinc-based sulphate electrolyte with incorporated composite particles of ZrO₂/SiC at 2.0 A/cm² for 10 min. The effects of particle on the mechanical properties were examined using scanning electron microscope attached with energy dispersion spectroscopy and atomic force microscopy. The micro-hardness and wear resistance behaviour were determined with high diamond micro-hardness tester and three body abrasive MTR-300 testers with dry sand rubber wheel apparatus with 5 N. The fabricated coating was thermally heated at 200 °C for 4 h to evaluate the coating stability. From the results, a modification in the microstructure and topographic orientation as a result of incorporated composite was noticed on the zinc matrix. The mechanical and thermal properties were observed to be considerably improved by the incorporation of the ZrO₂/SiC weight fraction. A significant improvement in wear and hardness properties were also obtained for the multiphase embedded coatings.