Wear characterization of electrodeposited Ni–WC composite coatings

The present contribution reports the tribological properties of Ni–WC composite coatings, electrodeposited on steel substrate. Commercial WC particles with an average size of 5 μm were codeposited with Ni on a mild steel substrate using a Watts bath at 50°C. The effect of plating variables on deposition behavior was studied. The amount of WC in the deposited layer decreased and plating efficiency increased with an increase in current density from 0.1 to 0.3 A/cm². The tribological properties of the coatings were studied using a small amplitude reciprocating friction wear tester. The addition of WC in Ni increases the microhardness of the electrodeposited coatings. An important result is that the presence of embedded WC particles in the electrodeposited coatings results in a much lower coefficient of friction (COF) of 0.34, when compared with pure Ni (COF 0.62) and mild steel (COF 0.54).     

Dry sliding wear of Cu–15Ni–8Sn alloy

Using a pin-on-disc apparatus, the wear behavior of Cu–15Ni–8Sn alloy aged for different periods of time at 400 °C was investigated under dry condition. The results showed the wear rate was inversely proportional to the hardness of the alloy, but the maximum wear resistance was not consistent with maximum hardness. The alloy contained about 10% (volume) cells precipitated along grain boundaries had the lowest wear rate. The friction coefficient was constant for different hardness. SEM micrographs of the debris and pin revealed that the removal process of surface material involved subsurface deformation, crack nucleation, crack propagation and delamination of the material.     

Frictional behaviour of oxygen diffusion hardened titanium in dry sliding against Co–28Cr–5W–4Fe–3Ni–1Si cobalt alloy

The results of conformal pin-on-disc tribological tests of a hard layer of the solid solution of oxygen in α-titanium sliding against a Co–28Cr–5W–4Fe–3Ni–1Si cobalt alloy counterspecimen are presented. The α-Ti(O) layer was diffusely produced over 2–8 h of oxidising in the superficial zone of a technical quality titanium specimen.The friction and wear responses of the system were recorded and the wear mechanisms were studied. Investigations of the material structure and chemical constitution in micro-areas of the titanium specimen, cobalt alloy counterspecimen and wear debris formed in dry sliding were performed with a Philips XL20 microscope equipped with an EDAX analyser. Crushing of the α-Ti(O) layer, lowering of the wear rate after comminution of the hard α-Ti(O) layer, local tack spots and fine powder wear particles, mostly Ti oxides, were detected at the beginning of each test. Gradual brittle fracture and decay by pulverising of the α-Ti(O) particles embedded in both mating surfaces, which occurred during the test, led to the increase of the wear rate of the couple and domination of microcutting and tack spots spalling after their partial oxidation. Finally, after the disappearance of the α-Ti(O) loose particles, adhesive junctions, metal transfer and smearing become leading wear mechanisms.     

The tribological behavior of Ni–Cu–Ag-based PVD coatings for hybrid bearings under different lubrication conditions

In a cryogenic environment, components like bearings with interacting surfaces in relative motion (tribosystems) often generate undesired heat and experience high wear. Because the properties of conventional bearing materials like stainless steel cannot be applied to this temperature range, the PVD coating based on metal–metal pairs with better frictional properties must be employed. To test the suitability of the Ni–Cu–Ag-based PVD coatings of hybrid bearings for liquid rocket engine turbopumps and to obtain reliable coating material data in the extreme environment, the tribological behaviors of coatings under the cryogenic fluid (liquid oxygen and liquid nitrogen) and water lubricated conditions are studied, respectively. In the paper, the specimens are in a vibrocryotribometer with the ball-on-plane contact type, and various running conditions in terms of lubricants, contacting loading, and contacting velocity are examined. The simulated experiment for testing the actual tribological performance of Ni–Cu–Ag-based PVD coatings for hybrid bearings is tested. The results of the tests indicate that the coatings can be suitable for cryogenic tribosystems of turbopumps. In the cryogenic environment, the volume wear rate of coatings increases rapidly with the contacting loading, but 15 min later, the volume wear volume of coatings turns into 2.5–15×10⁻⁴ mm³. Besides, under the liquid oxygen condition in simulating the liquid rocket engine turbopumps environment, the friction coefficients are 0.03–0.1.     

Tribological behaviour of diamond coatings sliding against Al alloys

A low wear rate, combined with exceptional physical properties, makes diamond an ideal candidate for the machining of non-ferrous materials. It is particularly interesting for tooling aluminium and its alloys as it offers these soft materials clean cutting and lets the shavings slide on the tool surface.It results from studies dealing with the friction of diamond against aluminium, that the tribological behaviour of this pair is greatly influenced by the presence of oxides, more particularly Al₂O₃, on the counterface surface. It was therefore necessary to better understand the role of these oxides during the cutting process, the way they modify the nature of the contact, and their effects on transferred layer formation.The tribological behaviour of diamond coatings prepared by the combustion flame process, sliding against aluminium alloys under different environments (vacuum, oxygen and water vapour), at two applied normal loads is presented here; the modifications of both the coatings (formation of amorphous carbon) and the counterfaces (depth of the friction track), as well as the transferred layers (chemical composition, aspect) are specifically studied.The surface changes are revealed by scanning electron microscopy observations. Raman spectroscopy and energy dispersive spectroscopy analyses were realised to highlight the observed phenomena.     

Tribological characterization of thin hard coatings by reciprocating sliding tests

Thin hard coatings on metal or ceramic surfaces offer a large spectrum of improvements of the friction and/or wear behaviour of tribosystems. The development of coatings and the tailoring of their properties require test methods providing information about their friction and wear behaviour. A new wear test standard (ASTM) is under development for the evaluation of friction and wear quantities for sliding motions using the reciprocating sliding mode. The applicability of this test method to coated specimens was checked by testing uncoated and coated steel specimens in contact with alumina balls, whereby lower loads were used than in the ASTM proposal for bulk materials. Additionally, the influence of the relative humidity of the surrounding air at room temperature on friction and wear results was examined.     

Effects of CeO2 on friction and wear characteristics of Fe–Ni–Cr alloy coatings

The effects of rare earth oxide CeO₂ on the microstructure and wear resistance of thermal sprayed Fe–Ni–Cr alloy coatings were investigated. The powders of Fe–Ni–Cr alloy with the addition of CeO₂ were flame sprayed on to a 1045 carbon steel substrate. The coatings were examined and tested for microstructure feature, compositions, and phase structure. Tribological properties of coatings were tested under reciprocating sliding test. The results were compared with those for coatings of the alloy without CeO₂. The comparison indicated that the addition of rare earth oxide CeO₂ could refine and purify the microstructure of coatings, and increase the microhardness of the coatings. As a result, by CeO₂ addition, the friction coefficient of the coatings was decreased slightly and the wear resistance of the coatings was enhanced significantly.     

Electron microscopy of Ag–(Ni–O) core–shell nanowires

This report provides information about an electrodeposition‐based two‐step synthesis methodology for producing core–shell Ag–(Ni–O) nanowires and their detailed structural and compositional characterization using electron microscopy technique. Nanowires were produced by employing anodic alumina templates with a pore diameter of 200 nm. In the first step of the synthesis process, nanocrystalline Ni–O was electrodeposited in a controlled manner such that it heterogeneously nucleated and grew only on the template pore walls without filling the pores from bottom upwards. This alumina template with pore walls coated with Ni–O was then utilized as a template during the electrodeposition of Ag in the second step. Electrodeposited Ag filled the template pores to finally produce Ag–(Ni–O) core–shell nanowires with an overall diameter of 200 nm.     

Dry sliding wear behaviour of cast high strength aluminium alloy (Al–Zn–Mg) and hard particle composites

This paper describes the results of dry sliding wear tests of aluminium alloy (Al–Zn–Mg) and aluminium (Al–Zn–Mg)–10, 15 and 25 wt.% SiCp composite was examined under varying applied pressure (0.2 to 2.0 MPa) at a fixed sliding speed of 3.35 m/s. The sliding wear behaviour was studied using pin-on-disc apparatus against EN32 steel counter surface, giving emphasis on the parameters such as coefficient of friction, rise in temperature, wear and seizure resistance as a function of sliding distance and applied pressure. It was observed that the wear rate of the alloy was noted to be significantly higher than that of the composite and is suppressed further due to addition of silicon carbide particles. The temperature rise near the contacting surfaces and the coefficient of friction followed reversed trend. Detailed studies of wear surfaces and subsurface deformation have been carried out. The wear mechanism was studied through worn surfaces and microscopic examination of the developed wear tracks. The wear mechanism strongly dictated by the formation and stability of oxide layer, mechanically mixed layer (MML) and subsurface deformation and cracking. The overall results indicate that the aluminium alloy–silicon carbide particle composite could be considered as an excellent material where high strength and wear resistance are of prime importance.     

Wear and immersion corrosion of Ni–P electrodeposit in NaCl solution

This paper presents an experimental study on the block-on-cylinder wear behavior of an electroplated Ni–P coating immersed in 5% NaCl solution at different temperatures and polarization potentials. The simply immersion corrosion without normal load was performed first, and then the corrosion effect on the wear behavior including friction coefficient, surface roughness and weight loss were discussed. It is found that the morphology nature of the corrosion film has crucial effect on the wear performance of the coating. Moreover, the bath temperature and the polarization potential greatly influence the formation of the corrosion film.     

Crystalline phases found in rapidly quenched Ni–Nb–Zr alloys

The properties of metallic alloys can be significantly improved by developing non‐equilibrium phases in the microstructures through rapid solidification techniques, thus the characterisation of these unusual structures is extremely important. In this research, the microstructures of three rapidly quenched alloys, namely Ni_65.2Nb_33.8Zr_1.0, Ni_54.8Nb_31.1Zr_14.1 and Ni_54.8Nb_21.6Zr_23.6 (at. %) were investigated in greater detail in order to determine the structures and compositions of their crystalline phases. These crystalline phases were characterised using a combination of scanning electron microscopy, energy dispersive x‐ray spectroscopy, x‐ray diffraction and transmission electron microscopy techniques. The phases were compared to the crystalline structures reported in the literature. Our results indicate some agreement with the Ni–Nb phase diagram and an isothermal section of the Ni–Nb–Zr phase diagram; however, it is detected zirconium solubility in the Ni₃Nb phase, as well as, the absence of expected crystalline phases.     

An examination of friction and sliding wear properties of Zn–40Al–2Cu–2Si alloy in case of oil cut off

In this work, four ingots of Zn–40Al–2Cu–2Si alloy were produced by permanent mould casting. Two of the ingots were subjected to quench-ageing treatment. After examining the microstructure and some mechanical properties of the alloy in both as-cast and heat treated conditions, its friction and wear behaviour were investigated over a range of pressure and sliding speed using a conforming block-on-ring type machine without oil supply which corresponds to “oil cut off”.It was observed that the heat treatment increased the hardness and tensile strength of the alloy. It was also observed that in the case of oil cut off the friction coefficient of the alloy decreased with increasing pressure up to approximately 3 MPa above which the trend reversed. However, the friction coefficient increased with increasing sliding speed after showing a small decrease with it, and the temperature of the wear sample increased with both pressure and sliding speed. It was shown that the wear loss of the alloy increased exponentially with pressure, but linearly with sliding speed. However, the increase in wear loss with sliding speed became exponential at pressures above 4 MPa.As a result of this work, it was concluded that the quench-ageing treatment does not increase only the hardness and tensile strength of Zn–40Al–2Cu–2Si alloy but also its wear resistance during running without oil supply.     

A study of the wear behavior of polymer–matrix composites containing discontinuous nanocrystalline alloy reinforcements

The tribological behavior of bakelite resin–matrix composites reinforced with nanocrystalline Al 6061 T6 particles produced by machining (grain size 70–500 nm) has been studied using block-on-ring and pin-on-disk tests. The polymer–matrix composite reinforced with nanostructured Al 6061 particles aged for 10 h [Al 6061 (3) 10 h] shows a wear reduction of around 60% with respect to the conventional microstructured reinforcement. Also it shows the lowest wear rates when compared with the nanostructured reinforcements aged for 5 h or 1 h, respectively. Friction coefficients and wear rates increased with increasing sliding speed and normal load. Under 10 N and 0.10 m s⁻¹, Al 6061 (3) 10 h showed an initial friction and contact temperature increase and a very severe wear with material transfer to the steel ball surface. Increasing the steel–composite contact temperature to 100 °C (1 N; 0.05 m s⁻¹) produced a one order of magnitude decrease both in friction and wear. Wear mechanisms for the polymer matrix and the aluminum reinforcement are discussed on the basis of SEM and EDS observations.     

Tribological behaviour of duplex treated Ti–6Al–4V: combining nitrogen PSII with a DLC coating

The chemical structure and tribological behaviour of Ti–6Al–4V plasma source ion implanted with nitrogen then DLC-coated in an acetylene plus hydrogen-glow discharge (bias voltage −10 to −30 kV) were investigated. The as-modified samples have a TiN/H:DLC multilayer architecture (coating resistivity 1.6×10⁹ to 2.4×10¹¹ Ω/cm) and exhibit higher hardness, especially at low loads or plastic penetrations in the order of deposition bias voltage −10, −20 and −30 kV. At a lower contact load (1 N) and higher sliding speed (0.05 m/s), frictional properties in most cases improved, as did wear properties. At a higher contact load (5 N) and lower sliding speed (0.04 m/s), friction showed almost no improvement, and wear properties deteriorated. When the material of the counterbody was then changed from AISI 52100 to Ti–6Al–4V modified as the disc (contact load 5 N unchanged, sliding speed decreased), the friction coefficient decreased (but showed no improvement compared with the unmodified sample), while wear properties deteriorated further, and wear was changed from just the disc to both disc and ball, abrasive and adhesive dominated. Transfer films, mainly made up of wear debris transferred from the disc wear surfaces, were formed on the wear scars of the counterbodies. The deterioration of wear properties of the modified samples at the higher contact load is considered to be caused by the “thin ice” effect.     

Correlations between microstructural parameters, micromechanical properties and wear resistance of plasma sprayed ceramic coatings

The micromechanical integrity of a ceramic plasma sprayed (PS) coating is determined by the size and distribution of the defects found in the coating, such as porosity, the inter-lamellar microcrack density, the intra-lamellar microcrack density as well as the lamellar, or splat, dimensions. In this work, several micromechanical tests were used to advance our understanding of the relationships between the different microstructural parameters found in PS ceramic coatings. The tests included depth sensing indentation, micro and macrohardness testing, and controlled scratch testing. Abrasive and erosive wear tests were performed on the same set of coatings, including plasma sprayed alumina and chromia, as well as sintered alumina as a reference material. The best correlations were found between the material hardness (H), the level of porosity (P) and the abrasive wear volume (W). Knoop hardness measurements provided the best correlation with wear data, followed by scratch hardness and Vickers hardness. An exponential function of the type W=k/Hⁿ was found, where k and n are constants. A similar function describes the correlation of wear volume with the elastic modulus of the coating. Fracture toughness could only be correlated with wear volume when combined with hardness in a function of the type W=k/H^0.5K_c^0.5. The incorporation into this function of a “microstructural factor” M=Pⁿ improves the correlation.     

Dry-sliding Tribological Properties of Nano-Eutectic Fe<Subscript>83</Subscript>B<Subscript>17</Subscript> Alloy

This paper reports the tribological performance of the nano-eutectic Fe₈₃B₁₇ alloy under dry sliding against Si₃N₄ ceramic ball in ambient environment with varying applied loads and sliding speeds. Worn surfaces of the nano-eutectic Fe₈₃B₁₇ alloy were examined with a scanning electron microscope (SEM) and an X-ray energy dispersive spectroscope (EDS). The wear debris of the samples were also analyzed by X-ray diffractometer (XRD). The wear rate of the nano-eutectic Fe₈₃B₁₇ alloy was of the magnitude of 10⁻⁴ mm³/m, which was lower than that of the coarse grained Fe₈₃B₁₇ alloy. The friction coefficient of the nano-eutectic Fe₈₃B₁₇ alloy was almost the same as that of the coarse grained Fe₈₃B₁₇ alloy. The Fe₂SiO₄ oxide layer was formed on the worn surface of the nano-eutectic Fe₈₃B₁₇ alloy. However, on the worn surface of the coarse grained Fe₈₃B₁₇ alloy was found only a little Fe₂SiO₄. These results demonstrated that the nanostructure improved the wear resistance of the Fe₈₃B₁₇ alloy, but did not significantly affect the friction coefficient. The wear mechanism of the nano-eutectic Fe₈₃B₁₇ alloy was delamination abrasion mainly.     

Tribological properties of hardened high strength Boron steel at combined rolling and sliding condition

The use of hardened high strength steel is found in applications where high wear resistance is required. The wear properties of high strength Boron steel are well known in applications with abrasive wear from stones, ore and other hard material. A unique concept of wear protection of rails is newly presented, a wear resistant cap made of hardened high strength Boron steel.Reducing the wear of rails and wheels and controlling the frictional behavior in the wheel/rail contact are two key issues for railway owners in order to reduce the increasing costs related to higher axle loads, higher speeds, more frequent traffic, etc. Therefore, the aim of this work has been to investigate and compare the tribological properties of Boron steel and UIC 1100 rail steel in contact with Blue Light wheel steel (AAR Class C (69-JDG-8)) under dry and water lubricated conditions in a two-disc tribometer. Advanced analytical instruments including 3D optical surface profiler, micro-hardness indenter, light microscope and SEM/EDS were used to analyze the results.Results from the experiments show that the friction coefficient in tests with Boron steel is more stable both in dry and water lubricated conditions than tests including UIC 1100 rail steel used in todays application. Surface damages seen from water lubricated tests on UIC 1100 rail steel are not seen on the surface of the Boron steel discs. In all tests, the wear decreased when water was added in the contact and friction was slightly decreased.     

Friction and wear properties of duplex MAO/CrN coatings sliding against Si3N4 ceramic balls in air, water and oil

It is evident that the micro-arc oxidation (MAO) ceramic coatings often exhibit relatively high friction coefficients as sliding against many mating materials. To reduce the friction coefficient for the MAO coatings, the duplex MAO/CrN coatings were deposited on 2024Al alloy using combined micro-arc oxidation and reactive radio frequency magnetron sputtering. The microstructure and phase of the duplex coatings were observed and determined using scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The friction and wear behaviors of the duplex coatings sliding against Si₃N₄ balls in air, water and oil were investigated using a ball-on-disk tribometer. The wear rate of the duplex coating was determined by non-contact optical profilometer and the wear tracks on the duplex coatings were observed by SEM. The results showed the CrN coatings mainly consisted of Cr, CrN and Cr₂N phases. The duplex coatings/Si₃N₄ tribopair exhibited the highest friction coefficient in air, while displayed the lowest friction coefficient in oil. When the normal load and the sliding speed increased, the friction coefficient in air increased from 0.65 to 0.72, whereas decreased from 0.58 to 0.36 in water and 0.20 to 0.08 in oil. The specific wear rates for the duplex coatings in air were higher than those in oil. In comparison to the MAO coatings, the duplex MAO/CrN coatings displayed excellent tribological properties under the same conditions.     

Wear of spray deposited Al–6Cu–Mn alloy under dry sliding conditions

The dry sliding wear of spray deposited Al–6Cu–Mn alloy was studied as a function of applied load in the range of 5–400 N. The variation of wear rate with applied load was obtained, from which four regions can be observed. On the basis of observations and analyses on the worn surface, the worn subsurface, the wear debris and friction coefficient, wear mechanism in different regions has been identified. Two wear regimes, i.e. mild and severe wear, were displayed in the entire applied load range. The transition from mild to severe wear occurred at a critical load. Mild wear involves three regions in the wear rate vs. load variation, and the wear in each region was controlled by different wear mechanism. With increasing load, the dominant wear mechanism in the period of mild wear displays successively oxidative wear, delamination and subsurface-cracking assisted adhesive wear. Severe wear was operated by the adhesive wear mechanism and the wear debris was formed by the shear fracture of subsurface material of the pin. The transition from mild to severe wear depended on the strength of the material of the pin adjacent to the contact surface and the strain-induced shear stress created by applied load.     

The erosion and abrasion characteristics of alumina coatings plasma sprayed under different spraying conditions

A series of plasma sprayed alumina coatings was evaluated regarding their erosion and abrasion characteristics. The coatings were deposited under different spraying conditions, using a commercial axial injection plasma spray system, and with powders of different grit sizes and crystallinity. A sintered bulk alumina and a conventionally sprayed coating, produced by a radial injection air plasma spray technique, were tested as reference materials. To evaluate the importance of energy input the coatings were produced using two different torch nozzle sizes and gas mixtures with a varied amount of hydrogen. The erosion and abrasion results indicate that hydrogen concentration, nozzle size and precursor powder type and size influence the tribological characteristics of the coatings. The wear resistance of the coatings seems to benefit from an increase in hydrogen concentration or torch nozzle size. The effect of precursor powder size on the wear resistance was more complex but indicates that sapphire powders of medium precursor sizes are advantageous to ordinary plasma spraying powders of alumina.