Tribological Behaviour of the Ceramic Coating Formed on Magnesium Alloy

Micro-arc oxidation is a recently developed surface treatment technology under anodic oxidation. Through micro-arc oxidation, a ceramic coating is directly formed on the surface of magnesium alloy, by which its surface property is significantly improved. In this paper, a dense ceramic oxide coating was prepared on an AZ31 magnesium alloy by micro-arc oxidation in a NaOH-Na2SiO3-NaB407-（NaPO3）6 electrolytic solution. Micro-structure, surface morphology and phase composition were analysed using scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The tribological behavior of the micro-arc oxidation ceramic coating under dry sliding against GCr15 steel was evaluated on a ball-on-disc test rig. The results showed that the AZ31 alloy was characterized by adhesion wear and scuffing under dry sliding against the steel, while the surface micro-arc oxidation ceramic coating experienced much abated adhesion wear and scuffing under the same testing conditions. The micro-arc oxidation ceramic coating showed good friction-reducing and fair antiwear ability in dry sliding against the steel.

Tribological behaviour of sintered iron based self-lubricating composites

This work is a review of previous works,presenting and discussing the most important results obtained by an ongoing research program towards the development of innovative,low-cost,self-lubricating composites with a low friction coefficient and high mechanical strength and wear resistance.Special emphasis is given to uniaxial die pressing of solid lubricant particles mixed with matrix powders and to metal injection moulding associated with in situ generation of solid lubricant particles.Initially,a microstructural model/processing route (powder injection moulding followed by plasma-assisted debinding and sintering) produced a homogeneous dispersion of in situ generated solid lubricant particles.Micrometric nodules of graphite with diameter smaller than 20 μm were formed,constituting a nanostructured stacking of graphite foils with nanometric thickness.Micro Raman analysis indicated that the graphite nodules were composed of turbostratic 2D graphite having highly misaligned graphene planes separated by large interlamellae distance.Large interplanar distance between the graphene foils and misalignment of these foils were confirmed by transmission electron microscopy and were,probably,the origin of the outstandingly low dry friction coefficient (0.04).The effect of sintering temperature,precursor content,metallic matrix composition and surface finish is also reported.Furthermore,the influence of a double-pressing/double-sintering (DPDS) technique on the tribological performance of self-lubricating uniaxially die-pressed hBN + graphite-Fe-Si-C-Mo composite is also investigated.Moreover,the tribological behaviour of die-pressed Fe-Si-C matrix composites containing 5,7.5 and 10 wt％ solid lubricants (hBN and graphite) added during the mixing step is analysed in terms of mechanical properties and wear mechanisms.Finally,the synergy between solid lubricant particles dispersed in a metallic matrix and fluid lubricants in a cooperative mixed lubrication regime is presented.

Experimental and modelling studies of the transient tribological behaviour of a two-phase lubricant under complex loading conditions

The transient tribological phenomenon and premature lubricant breakdown have been widely observed in metal forming,leading to excessive friction at the contact interfaces.In this research,the transient tribological behaviour of a two-phase lubricant were studied under complex loading conditions,featuring abrupt interfacial temperature,contact load,and sliding speed changes,thus representing the severe interfacial conditions observed in warm/hot metal forming applications.The strong experimental evidence indicates that the evolution of friction was attributed to the physical diminution and chemical decomposition effects.As such,a visco-mechanochemical interactive friction model was developed to accurately predict the transient tribological behaviour of the two-phase lubricant under complex loading conditions.The new friction model exhibited close agreements between the modelling and experimental results.

Tribological behaviour of the green anode paste with a steel plate at 150 ℃

In order to accurately predict the mechanical behaviour of paste during forming process,the friction law between the carbon paste and the mould wall is an important parameter to be determined.This paper presents the tribological behaviour of the lubricated paste/steel interface subjected to high stress conditions at the anode forming temperature of 150℃.A method to characterize the tribological behaviour has been developed and an apparatus was built.The method is based on the comparison of two successive experiments.In the first experiment,the paste is in contact with the friction plate.In the second one,a layer of Teflon is placed under the paste in order to excite another parameter thereby allowing the identification of the friction coefficient between the paste and steel wall.These experiments were performed with a paste under different normal loads.The static and kinetic friction coefficients of the Teflon/steel,steel/steel and paste/steel interfaces have been estimated.The static and kinetic friction coefficients of the Teflon/steel are respectively 0.17 and 0.13.The steel/steel friction coefficients were evaluated twice which gave a static coefficient that varies between 0.22 and 0.30.The kinetic coefficient varies between 0.18 and 0.25.The static and kinetic paste/steel friction coefficients obtained from both experiments are clearly similar.Their values are 0.15 and 0.13 respectively.

Influence of CaCO_3 Whisker Content on Mechanical and Tribological Properties of Polyetheretherketone Composites

The mechanical and tribological properties of polyetheretherketone （PEEK） composites filled with CaCO3 whisker in various content of 0～45% （wt pct） were investigated. The composite specimens were prepared by compression molding. Tribological testing of composites in dry wear mode against carbon steel ring was carried out on a MM200 block-on-ring apparatus. Data on neat PEEK were also included for comparison. It was observed that inclusion of CaCO3 whisker affected the most mechanical properties and the friction and wear in a beneficial way. With an increase in CaCO3 whisker content, friction coefficient continuously decreased but the trends in wear performance varied. The specific wear rate showed minima as 1.28×10^-6 mm^3/Nm for 25% CaCO3 whisker inclusion followed by a slow increase for further CaCO3 whisker addition. In terms of friction applications, when the tribological and mechanical properties are combined, the optimal content of CaCO3 whisker in the filled PEEK should be recommended as 15% to 20%. Fairly good correlations are observed in friction coefficient vs bending modulus and wear rate vs bending strength, confirming that the bending properties prove to be the most important tribology controlling parameters in the present work.

Effect of sintering temperature on structure and tribological properties of nanostructured Ti-15Mo alloy for biomedical applications

The effect of sintering temperature(1073?1373 K)on the structural and tribological properties of nanostructured ballmilledβ-type Ti?15Mo samples was investigated.The prepared samples were characterized using various apperatus such as X-ray diffractometer,scanning electron microscope(SEM)and ball-on-plate type oscillating tribometer.Wear tests were conducted under different applied loads(2,8 and 16 N).Structural results showed that the mean pore and crystallite size continuously decreased with increasing sintering temperature to reach the lowest values of 4 nm and 29 nm at 1373 K,respectively.The relative density of the sintered sample at 1373 K was as high as 97.0%.Moreover,a higher sintering temperature resulted in higher relative density,greater hardness and elastic modulus of the sample.It was observed that both the friction coefficient and wear rate were lower in the sample sintered at 1373 K which was attributed to the closed porosity.

Properties of polydimethylsiloxane hydrophobic modified duplex microarc oxidation/diamond-like carbon coatings on AZ31B Mg alloy

A reliable,high-performance coating procedure was developed using PDMS to modify a duplex MAO/DLC coating on an AZ31B Mg alloy.First,the duplex MAO/DLC coating was fabricated via a combined MAO and unbalanced magnetron sputter process.Subsequently,a PDMS solution was used to modify the MAO/DLC coating via a conventional dip-coating method.The surface characteristics,bond strength,hardness,tribological behaviour,and corrosion resistance of the coated samples were evaluated via SEM,CA,Raman spectroscopy,friction and wear behaviour,polarisation curve,and NSS tests.The PDMS modification reduced the HIT of MAO/DLC coating from 15.96 to 8.34GPa;this is ascribed to the penetration of PDMS,which has good rheological properties to form a viscoelastic Si-based organic polymer layer on the MAO/DLC coating.However,the PDMS-modified MAO/DLC coating was denser,hydrophobic,and had higher bond strength compared with MAO-and MAO/DLC-coated samples.Moreover,the PDMS modification reduced the COF and wear rate of the duplex MAO/DLC coating.This indicates that the PDMS improved the tribological behaviour owing to the transferred Si oxide that originated from the Si-O network of the PDMS,as well as the low graphitisation of the DLC layer during sliding.Furthermore,the corrosion current density of the MAO/DLC-coated sample modified by PDMS for 10min decreased by two order of magnitude compared with that of the MAO/DLC-coated sample but by five orders of magnitude compared with that of the bare substrate.The NSS tests proved that the PDMS layer slowed the corrosion of the Mg alloy under long-term service,enhancing the corrosion protection efficiency.The results are attributed to the high bond strength and lubricant MAO/DLC layer,and the dual role of sealing and hydrophobicity of PDMS.Therefore,PDMS modification is promising for the fabrication of protective materials for Mg alloys that require corrosion and wear resistance.

Tribological and Physicochemical Analysis of Squid Pen High-density Polyethylene Biocomposite for Medical Application

High-Density Polyethylene(HDPE)wear debris generated in the hip joint prothesis leads to its loosening.The aim of this study was to evaluate the potential of Squid Pen(SP)on the tribological and physicochemical properties of HDPE matrix.Biocomposites filled with 0,5,10,15 and 20 wt.%SP were elaborated by hot compression molding.Wear tests were carried out using a reciprocating pin-on-disc tribometer.Rockwell hardness,Fourier-Transform infra-red(FTIR)analysis,Scanning Electron Microscopy(SEM)of the biocomposite were analysed.FTIR analysis results of the biocomposites showed that an increase in the crystallinity rate was obtained with the addition of SP filler.Only 10 wt.%of SP has a significant effect on the hardness of the composite.The correlation between the friction coefficient and the wear resistance of the composite was investigated.The 5 wt.%SP-HDPE biocomposite has the lowest friction coefficient value with a decrease in the specific wear rate,compared to the unfilled HDPE.The SEM results showed that SP wear debris played an important role as a third roller body at the interface reducing the friction coefficient of the composite.It was concluded that the HDPE biocomposite could be successfully reinforced with 5 wt.%of SP.