Mechanical Characteristics and Adhesive Strength of Nickel–Chromium Coatings Applied by Laser Cladding

Russian Engineering Research - The mechanical characteristics and adhesive strength of nickel–chromium coatings produced by the laser fusion of Ni12CrFe and PR-NiCr16SiB3 powder are compared...     

Investigation of the Structure of Surface and Tribological Properties of Composition Coatings Based on Thermosetting Epoxy–Polyester Resins

Composition coatings based on the epoxy–polyester matrix and polydisperse particles of structured carbon have been investigated. The formulation of the mixed compositions has been optimized. The effect of filler particles on structure formation of the surface and tribotechnical characteristics of composition coatings has been shown.     

Test Analysis of Friction Couples With Solid Lubricant Coatings under Ground–Space Conditions and Prediction of Tribological Characteristics

As a result of an analysis of the literature data on ground–space tribological tests of friction couples with solid lubricant coating (SLC) ARSRI PP 212, the dependences for evaluating the starting antifriction characteristics have been determined. The wear life and coefficient of friction have been compared. According to results, calculation algorithms of tribological characteristics of friction couples with SLC for considered operational conditions have been developed and implemented.     

Carrying Capacity of a Threaded Pair Made of Spatially Reinforced Carbon–Carbon Composite

Russian Engineering Research - The carrying capacity of a threaded pair made of spatially reinforced carbon–carbon composite with 4DL reinforcement is determined experimentally in the range...     

Frictional Interaction of Carbon–Carbon Composites with Steel at High Temperatures

Russian Engineering Research - The frictional interaction of carbon–carbon composites with steel at high temperatures is considered. The antifrictional properties of carbon–carbon...     

Atomic Force Microscope Investigation on Static Nanomechanical Properties Versus Dynamic Nanotribological Evaluation of Metal–ZrN and ZrN Thin Films

The present study offers for the first time a correlation between static nanomechanical properties (nanohardness (H), elastic modulus (E), H/E and H ³/E ² ratio) and dynamic properties (resulting from nanoscratch measurements) for Metal–ZrN thin films (Inconel–ZrN, Cr–ZrN and Nb–ZrN) as well as monolayer polycrystalline ZrN thin films. Metal–ZrN thin films have a great industrial potential, as they can combine high hardness with good elasticity and toughness making them effective for wear resistant application. Nanomechanical and nanotribological properties of Metal–ZrN and ZrN thin films deposited by DC unbalanced magnetron sputtering were investigated using an atomic force microscope interfaced with a Hysitron Triboscope. The elastic recovery of thin films under a normal load applied during nanoindentation was evaluated and correlated with elastic recovery of thin films under dynamic loading during nanoscratch measurements in order to asses which film compositions provide superior wear resistance. It is demonstrated that dynamic elastic recovery measurements correlated well with those derived from static nanoindentation tests. The nanoscratch test combines both normal and tangential loading, therefore, it is expected to be an even better predictor of wear-resistance. The AFM nanoindentation and nanoscratch measurements show superior nanomechanical and nanotribological properties for Metal–ZrN thin films when compared to polycrystalline ZrN thin films.     

Production of Nickel–Chromium Coatings from Powder by Laser Cladding

Russian Engineering Research - The use of self-fluxing Ni12CrFe and NiCr16SiB3 powder in laser cladding within a protective atmosphere (argon) is considered. The characteristics of the powder are...     

Influence of Parameters of Reactive Magnetron Sputtering on Tribomechanical Properties of Protective Nanostructured Ti–Al–N Coatings

The influence of substrate temperature and bias voltage on the structure and tribomechanical properties of the Ti–Al–N coatings obtained by reactive magnetron sputtering technique has been investigated. The structure and elemental and phase compositions have been studied by scanning electron microscopy, Rutherford backscattering, and X-Ray diffraction. The results of friction and wear experiments indicated that the lowest coefficient of friction (three times lower than 12Cr18Ni10Ti) corresponded to a coating deposited at a bias voltage of–200 V and a substrate temperature of 340°С, while the most wear-resistant coating (under a load of 700 mN and the testing time of 1080 s) was Ti–Al–N sputtered at a bias voltage of–200 V and a substrate temperature of 440°С.     

The Contribution of Thin PFPE Lubricants to Slider–Disk Spacing

We have investigated the effect of the molecular weight (MW) and film thickness of a perfluoropolyether lubricant, Zdol, on the slider–disk spacing loss, or clearance. The major conclusion of this work is that Zdol films as thin as 10 Å can reduce the slider–disk clearance by 2 nm or more in the molecular weight range of 1000–5000 amu. This is attributed to the attractive van der Waals interaction between the slider and the disk surface that causes the Zdol main chain to interact with the slider surface, giving rise to a friction force. When the film thickness of the lubricant exceeds the monolayer thickness, dewetting can take place. The droplets that form occupy the space between the slider and disk surface reducing the slider–disk clearance by as much as 4 nm. There is a step increase in the acoustic emission signal at the dewetting thickness transition, indicative of a slider–disk interference.     

Chromium and Detonation Nanodiamond Based Coatings of the Chromium–Carbon System: Deposition by Magnetron Sputtering,Peculiarities of Phase Composition,and Tribological Properties

The structure, the chemical and phase compositions, and the micromechanical and tribological properties of chromium–carbon coatings obtained by the magnetron sputtering of composite and/or sintered chromium–nanodiamond targets are investigated. The coatings possess the composite multiphase structure composed of chromium and its phases formed as a result of the chemical interactions of the target material’s components both between each other and with the reactive gas if present in a sputtering atmosphere. Several technological factors influencing the structural and phase peculiarities of the coatings, their nanohardness, and the dry friction behavior at high contact pressures are studied.     

Wear Resistance of Nickel–Cobalt–Polytetrafluoroethylene Composite Electrolytic Coatings Deposited from Chloride-Containing Electrolyte

The development and implementation of novel galvanic coatings with abnormally high microhardness, wear resistance, and corrosion resistance are the focus of modern machine-building. The galvanic deposition of composite electrolytic coatings (CECs) is an efficient method of improving their properties. In this paper, a chloride-containing electrolyte has been proposed for obtaining a wear-resistant nickel–cobalt–polytetrafluoroethylene CEC. The effect exerted by electrolysis modes and electrolyte compositions on some physicomechanical properties (wear resistance and corrosion resistance) of a nickel–cobalt–polytetrafluoroethylene composite electrolytic coating deposited from chloride-containing electrolyte has been studied. The potentialities of using the deposited layer as wear- and corrosion-resistant coating.     

High Temperature Tribological Characteristics of Fe–Mo-based Self-Lubricating Composites

Fe–Mo-based self-lubricating composites were prepared by a powder metallurgical hot-pressing method. The tribological properties of Fe–Mo-based composites with varied CaF₂ contents at high temperature were evaluated, and the effect of glaze films on the friction and wear characteristics of composites were analyzed. The results show that the introduction of CaF₂ into Fe–Mo alloys improved the mechanical properties, and the best tribological properties of Fe–Mo–CaF₂ composites were achieved at the CaF₂ content of 8 wt% at both room temperature and 600 °C. The worn surface of Fe–Mo–CaF₂ composite at 600 °C is characterized to plastic deformation and slight scuffing, and the improved tribological properties are attributed to the formation of lubricious glaze film that composed of high-temperature lubricants CaMoO₄ and CaF₂ on the worn surface of the composites.     

Effect of Operating Conditions on Tribological Response of Al–Al Sliding Electrical Interface

Aluminum is widely used in electrical contacts due to its electrical properties and inexpensiveness when compared to copper. In this study, we investigate the influence of operating conditions like contact load (pressure), sliding speed, current, and surface roughness on the electrical and tribological behavior of the interface. The tests are conducted on a linear, pin-on-flat tribo-simulator specially designed to investigate electrical contacts under high contact pressures and high current densities. Control parameters include sliding speed, load, current, and surface roughness. The response of the interface is evaluated in the light of coefficient of friction, contact resistance, contact voltage, mass loss of pins, and interfacial temperature rise. As compared to sliding speed, load, and roughness, current is found to have the greatest influence on the various measured parameters. Under certain test conditions, the interface operates in a “voltage saturation” regime, wherein increase in current do not result in any increase in contact voltage. Within the voltage saturation regime the coefficient of friction tends to be lower, a result that is attributed to the higher temperatures associated with the higher voltage (and resulting material softening). Higher interfacial temperatures also appear to be responsible for the higher wear rates observed at higher current levels as well as lower coefficients of friction for smoother surfaces in the presence of current.     

Tribological Performance of PTFE–Metal Binary Coatings in Rolling/Sliding Contact

Tribological performance of surface coatings with embedded PTFE reservoirs in rolling/sliding contact is reported. Using two different coating materials and two shapes and patterns of PTFE reservoirs test samples in the form of discs were prepared and tested in a four-ball contact configuration under loads corresponding to nominal contact pressure of 0.5 and 1.0 GPa. It was found that one coating, namely aluminium–bronze with embedded PTFE reservoirs is suitable for applications where rolling is also associated with a degree of sliding and there is no external lubrication.     

Relative Wear of Copper–Graphite Composite Electrodes in Electrical Discharge Machining

Russian Engineering Research - The influence of the pulse energy on the performance of copper electrodes with added graphite in the electrospark piercing of tool steel is studied. With increase in...     

Frictional Coefficient in Upsetting of a Thin Rigid–Plastic Plate of Square Cross Section

Russian Engineering Research - Abstract—A method is developed for calculating the frictional coefficient in the upsetting of a plate. Experiments confirm the calculations.     

Arc Evaporation of Ti–Al–Ta–N Coatings: The Effect of Bias Voltage and Ta on High-temperature Tribological Properties

Recently, titanium aluminium tantalum nitride (Ti–Al–Ta–N) coatings have been shown to exhibit beneficial properties for cutting applications. However, the reason for the improved behaviour of these coatings in comparison to unalloyed Ti–Al–N is not yet clear. Here, we report on the tribological mechanisms present in the temperature range between 25 and 900 °C for this coating system, and in particular on the effect of the bias voltage during deposition on the tribological response. Based on these results, we provide an explanation for the improved performance of Ta-alloyed coatings. An industrial-scale cathodic arc evaporation facility was used to deposit the coatings from powder metallurgically produced Ti₄₀Al₆₀ and Ti₃₈Al₅₇Ta₅ targets at bias voltages ranging from −40 to −160 V. X-ray diffraction experiments displayed a change with increasing bias voltage from a dual-phase structure containing cubic and hexagonal phases to a single-phase cubic structure. Investigations of the wear behaviour at various temperatures showed different controlling effects in the respective temperature ranges. The results of dry sliding tests at room temperature were independent of bias voltage and Ta-alloying, where the atmosphere, i.e. moisture and oxygen, were the most important parameters during the test. At 500 °C, bias and droplet-generated surface roughness were identified to determine the tribological behaviour. At 700 and 900 °C, wear depended on the coating’s resistance to oxidation, which was also influenced by the bias voltage. In conclusion, Ta-alloyed coatings show a significantly higher resistance to oxidation than unalloyed Ti–Al–N which could be an important reason for the improved performance in cutting operations.     

Role of Third Bodies in Friction and Wear of Cold-Sprayed Ti and Ti–TiC Composite Coatings

Titanium (Ti) and Ti-based alloy wear performance is often poor unless coating or lubricants are used. An alternative is to use hard phase reinforcement. Cold spray is a relatively new method to deposit composite coatings, where here we report the deposition of a Ti–TiC coating and its sliding wear behavior. Mixtures of mechanically blended Ti–TiC with various TiC content were injected into a de Laval nozzle and sprayed onto substrates. Two composite coatings and a pure Ti coating are reported here, where the as-sprayed compositions of the composites were 13.8 and 33.4 vol% TiC. Reciprocating dry sliding wear was performed using a custom-built in situ tribometer. All tests were conducted with a sliding speed of 3 mm/s and at a normal load of 0.5 N. Using a transparent sapphire hemisphere of 6.25 mm as counterface, dynamic behavior of third bodies was directly observed. It was found that adhesive transfer of Ti was the primary wear mechanism for the Ti coating, with oxidative and abrasive wear also occurring for longer sliding cycles. The superior wear resistance of the composite coatings compared to Ti was related to dual function of TiC particles, where they reinforced the Ti matrix and facilitated the formation of a stable and protective tribofilms. The tribofilms contained carbonaceous material that provided easier shear and lower friction. The formation of these tribofilms was highly dependent on the TiC particles, which contained excess carbon compared to the equilibrium composition. Higher TiC content was more effective in quickly developing and sustaining the tribofilms.     

Effects of NBR Particle Size on Performance of Carbon Fiber–Reinforced Paper-Based Friction Material

In the present work, three different sized nitrile–butadiene rubber (NBR) particles were used to modify carbon fiber–reinforced paper-based friction material (CFRPF). The effects of NBR particle size on performance of CFRPF were studied. The microstructure and properties of the samples were investigated by scanning electron microscopy, thermal analysis, and wet friction performance testing. Experimental results indicated that there were four stages in the thermal degradation of NBR-modified CFRPF. NBR particle size had a great effect on the first degradation stage (100–300°C). The highest friction coefficient was obtained with the sample containing the finest NBR particles. The wear rate of the friction materials decreased with an increase in NBR particle size. However, NBR particle size had little influence on the wear rate of the couple plate. The sample containing coarse NBR particles showed excellent friction stability under oil-lubricated conditions.