Research on swing friction lubrication mechanisms and the fluid load support characteristics of PVA–HA composite hydrogel

Hydrogel has been extensively studied for use as articular cartilage. This study aims to investigate fluid load support mechanism of polyvinyl alcohol–hydroxyapatite composite hydrogel. Finite element method is used to study swing friction lubrication mechanism and fluid load support. The friction coefficient increases with contact load and swing angle. The fluid flow has an important effect on the fluid load support, which decreases with an increase in contact load and swing angle. The fluid load support is very high (85%), and the hydrogel has low friction coefficient. It exhibits biphasic and self-generating lubrication mechanism.     

The effects of nickel and carbon concentrations on the wear resistance of Fe–Ni–C austenitic alloys

The effects of nickel and carbon concentrations on the wear resistance of Fe–xNi–yC (x = 14–20 wt.%, y = 0.6–1.0 wt.%) were investigated with respect to strain energy initiation of the martensitic transformation and hardness. The strain energy needed to initiate the martensitic transformation increased with increasing carbon and nickel concentrations, except in 1.0 wt.% C alloys. The wear resistance of the material decreased with increasing carbon concentration up to 0.9 wt.% C. This effect is most likely due to decrement of the martensite volume fraction with increasing carbon concentration induced by the incremental strain energy required to begin the martensitic transformation. In the case of 1.0 wt.% C, the improved wear resistance may be due to carbide precipitation.     

Effects of cold working and heat treatment on microstructure and wear behaviour of Cu–Be alloy C17200

The effects of cold work process between aging and solution heat treatment on the microstructure, hardness and the tribologic behaviour of a copper–beryllium (Cu–Be) alloy C17200 were investigated. The wear behaviour of the alloys was studied using ‘pin on disc’ method under dry conditions. The results show that the formation of fine grained structure and γ phase particles enhances the mechanical properties of the alloy; nonetheless, they do not reduce the wear rate. This is attributed to the capability of the softer specimens to maintain oxygen rich compounds during the dry sliding test.     

Effects of strain induced martensitic transformation on the cavitation erosion resistance and incubation time of Fe–Cr–Ni–C alloys

The effect of a strain-induced martensitic transformation on the cavitation erosion resistance and incubation time of Fe–10Cr–10Ni–xC (x = 0.3, 0.4, 0.5, and 0.6 wt%) austenitic steels has been studied. As the carbon concentration increased, mass loss in the alloys also increased, while the incubation period and the amount of transformed martensite decreased. In addition, the martensite volume fraction increased with increasing testing time and reached a saturation point for each test alloy. After the saturation point was reached, the martensite volume fraction did not change throughout the remainder of the test, even though the transformed martensite phase was removed. This result indicates that new martensite phases were formed immediately after the removal of the previously formed martensite. Martensitic transformation exerts significant effects on wear resistance and incubation time by steadily absorbing the cavity collapse energy.     

On the role of sliding load and heat input conditions in friction stir processing on tribology of aluminium alloy–alumina surface composites

ABSTRACT

Aluminium (AA5083)-alumina surface composites are prepared by friction stir processing in two conditions of heat input. The low heat (LH) input conditions is achieved at a rotational speed of 710?rpm and a traverse speed of 100?mm/min, and high heat (HH) input conditions are achieved at a rotational speed of 1400?rpm and a traverse speed of 40?mm/min. The tribological characteristics of aluminium alloy, friction stir processed (FSPed) alloy and FSPed surface composites against steel ball are studied at 5, 10 and 20?N load. While no significant influence is found on frictional behaviour, wear resistance of FSPed composites is superior to FSPed alloys. FSPed composites fabricated at HH input conditions exhibited improved wear resistance as compared to LH input condition. Adhesion and delamination are dominant wear mechanisms at 20?N. Debris particles are reduced in size and hydroxidated in sliding of surface composites.     

Erosion-oxidation of uncoated,aluminized and chromized-aluminized 9Cr–1Mo steels under fluidized-bed conditions at 550–700 °C

Protective coatings, deposited mainly by thermal spraying and diffusion techniques, are considered a solution to extend the lifetime of many components in the energy production sector, such as heat exchangers. In this paper, some results are presented for uncoated, aluminized and chromized-aluminized 9Cr–1Mo steel, subjected to air and to impacts by 200 μm silica particles at angles of 30° and 90° and speeds of 7.0–9.2 m s^?1 at 550 –700 °C, in a laboratory fluidized-bed rig, to determine whether or not aluminized and chromized-aluminized diffusion coatings could protect the steel under such conditions. Erosion-oxidation damage was characterized by measurement of the mean thickness changes using a micrometer and examination of worn surfaces by scanning electron microscopy.Under most conditions, the coatings provided some protection to the substrate: under 30° impacts, up to 650 °C, and under 90° impacts, at 700 °C, both coatings were effective, whereas under 90° impacts, up to 650 °C, only the chromized-aluminized coating gave significant protection. However, for 30° at 700 °C, the oxide scale on the substrate was protective and the coatings were not needed. Explanations for these observations are presented in this paper, in terms of interactions between the erosion and oxidation processes for the materials.     

Effect of as-ground surface and the BALINIT® C and Nb–S coatings on contact fatigue damage in gears

The influence of as-ground surface and the BALINIT^® C and Nb–S coatings on contact fatigue damage have been investigated using testing of case-carburised S156 steel helical gears. The micro-surface features on the as-ground gear flank tend to initiate micro-pitting. In BALINIT^® C coated gears, the surface irregularities are removed by polishing effect resulting in small scale initiation of micro-pitting at the interface between polished and unpolished regions. In Nb–S coated gears, the coating tends to penetrate and fill-up the surface micro-valleys and hence showed only scattered micro-pitting. The Nb–S coated gears did not produce any tooth profile loss whilst the BALINIT^® C coated gears produced profile loss. However, both BALINIT^® C and Nb–S coated gears show enhanced contact fatigue performance.     

Spatially resolved nanoscale chemical and mechanical characterization of ZDDP antiwear films on aluminum–silicon alloys under cylinder/bore wear conditions

summary  Understanding the lubrication of aluminum–silicon (Al–Si) alloys (>18 Si) under conditions similar to those in the cylinder/bore system is vital to determining their applicability to current engine designs. A novel investigation of the location of zinc-dialkyl-dithiophosphate (ZDDPs) antiwear (AW) film formation on an Al–Si alloy has been performed using X-ray absorption near edge structure (XANES) analysis, X-ray photoelectron emission spectroscopy (X-PEEM), and imaging nanoindentation techniques. A study of the initial stages of wear (10 min) to prolonged rubbing (60 min) was performed. The findings show that the film forms primarily on the raised silicon grains and is consistent with a zinc polyphosphate glass. The film has an elastic modulus of ~70 GPa and a similar elastic response to a ZDDP AW film formed on steel under the same conditions. This provides the first direct observation and characterization of a ZDDP antiwear film on Al–Si alloys using spatially resolved chemical and mechanical techniques at the nanoscale.     

Experimental investigations of mechanical properties and slurry erosion behaviour of high velocity oxy fuel and plasma sprayed Cr2O3–50%Al2O3 coatings on CA6NM turbine steel under hydro accelerated conditions

Slurry erosion behaviour of HVOF (High Velocity Oxy Fuel) and plasma sprayed coatings on CA6NM hydraulic turbine steel has been investigated at different levels of various parameters. The Cr₂O₃–50%Al₂O₃ composite powder was prepared and deposited on CA6NM steel samples to get the uniform thickness coatings. The surface roughness, porosity and microhardness of as-coated samples were measured. The as-coated samples were subjected to SEM/EDS analysis to evaluate the surface microstructure of the developed coatings. Erosion tests were performed on self made erosion test rig under hydro accelerated conditions. The study reveals that the velocity, impact angle and slurry concentration were the most significant parameters, influencing the erosion rate of these coatings. The average particle size had least affect on the erosion rate. HVOF-coated samples showed better corrosion resistance as compared to plasma-coated samples due to high hardness of HVOF-coated CA6NM samples.     

Environmental Effects on the Tribology and Microstructure of MoS<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–C Films

The tribology of molybdenum disulfide (MoS₂)–Sb₂O₃–C films was tested under a variety of environmental conditions (ambient 50% RH, 10⁻⁷ Torr vacuum, 150 Torr oxygen, and 8 Torr water) and correlated with the composition of the surface composition expressed while sliding. High friction and low friction modes of behavior were detected. The lowest coefficient of friction, 0.06, was achieved under vacuum, while sliding in 8 Torr water and ambient conditions both yielded the highest value of 0.15. Water vapor was determined to be the environmental species responsible for high friction performance. XPS evaluations revealed a preferential expression of MoS₂ at the surface of wear tracks produced under vacuum and an increase in Sb₂O₃ concentration in wear tracks produced in ambient air (50% RH). In addition, wear tracks produced by sliding in vacuum exhibited the lowest surface roughness as compared to those produced in other environments, consistent with the picture of low friction originating from well-ordered MoS₂ layers produced through sliding in vacuum.