Effect of SiC particles on the friction and wear behavior of Ti3Si(Al)C2-based composites

The non-lubricated, sliding friction and wear behavior of Ti₃Si(Al)C₂ and SiC-reinforced Ti₃Si(Al)C₂ composites against AISI 52100 bearing steel ball were investigated using a ball-on-flat, reciprocating tribometer at room temperature. The contact load was varied from 5 to 20 N. For monolithic Ti₃Si(Al)C₂, high friction coefficients between 0.61 and 0.90 and wear rates between 1.79 × 10⁻³ and 2.68 × 10⁻³ mm³ (N m)⁻¹ were measured. With increasing SiC content in the composites, both the friction coefficients and the wear rates were significantly decreased. The friction coefficients reduced to a value between 0.38 and 0.50, and the wear rates to between 2.64 × 10⁻⁴ and 1.93 × 10⁻⁵ mm³ (N m)⁻¹ when the SiC content ranged from 10 to 30 vol.%. The enhanced wear resistance of Ti₃Si(Al)C₂ is mainly attributed to the facts that the hard SiC particles inhibit the plastic deformation and fracture of the soft matrix, the oxide debris lubricate the counterpair, and the wear mode converts from adhesive wear to abrasive wear during dry sliding.     

A comparison of tribological properties of evenly distributed and agglomerated diamond nanoparticles in lubricated high-load steel–steel contact

The tribological properties of evenly distributed and agglomerated nanodiamonds on steel contact surfaces were compared in ethylene glycol lubricated tests using a pin-on-disc tribometer with a steel counter ball. The nanodiamond distributions were studied on silicon and steel surfaces using scanning electron microscopy. Friction and wear decreasing effects were observed with both sprayed and agglomerated nanodiamonds. The average friction coefficient with pure ethylene glycol lubricated contacts decreased from 0.16 to 0.12 with agglomerated nanodiamonds when 100 N load was applied. A minimum for both disc wear rate (0.40×10⁻⁶ mm³/Nm) and ball wear rate (0.29×10⁻⁶ mm³/Nm) was observed with agglomerated nanodiamonds. One of the mechanisms of nanodiamond lubrication was observed to be the incorporation of nanodiamond particles in to the tribolayer.     

Tribological properties of Ni-17.5Si-29.3Cr alloy at room and elevated temperatures

The tribological properties of Ni-17.5Si-29.3Cr alloy against Si₃N₄ were studied on a ball-on-disc tribotester between room temperature and 1000 °C. The effects of temperature on the tribological properties of the alloy were investigated. The worn surfaces of the alloy were examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that the tribological behavior of the alloy expressed some differences with increase in testing temperature. At low and moderate temperatures (below 800 °C), the alloy showed excellent wear and oxidation resistances, and the wear rate of the alloy remained in the magnitude of 10^?5 mm³/Nm; but at elevated temperature (800–1000 °C), the wear and oxidation resistances decreased, and the wear rate of the alloy increased up to 10^?4 mm³/Nm. The friction coefficient decreased from 0.58 to 0.46 with the rising of testing temperature from 20 to 600 °C, and then remained nearly constant. The wear mechanism of the alloy was mainly fracture and delamination at low and moderate temperatures, and transformed to adhesive and oxidation at elevated temperatures.     

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.     

Tribological behavior of PEEK components with compositionally graded PEEK/PTFE surfaces

PEEK is a high strength engineering thermoplastic that suffers from a high friction coefficient and a friction induced wear mode. Past studies with 10 μm PEEK and PTFE powders resulted in composite solid lubricant that (at the optimal composition) had a wear rate of k = 2 × 10⁻⁹ mm³/Nm with a friction coefficient of μ = 0.12. A compositional grading of PEEK and PTFE is implemented in this study to create a bulk composite with the functional requirements of component strength, stiffness and wear resistance while providing solid lubrication at the sliding interface. The tribological performances of three functionally graded PEEK components were evaluated on linear reciprocating, rotating pin-on-disk and thrust washer tribometers. Wear rates comparable to samples of the bulk solid lubricant and comparable or improved frictional performance were achieved by compositionally grading the near surface region of PEEK components.     

Study of TiAlSiN coatings post-treated with N and C + N ion implantations. Part 2: The tribological analysis

Ion implantation has found to be an effective approach to modify surface properties of materials. The present research investigates the effect of (1) nitrogen (N), and (2) carbon subsequently with nitrogen (C + N) implantations on the mechanical and tribological properties of the titanium–aluminium–silicon–nitride (Ti–Al–Si–N) coatings. Superhard TiAlSiN coatings produced by magnetron sputtering, of approximately 2.5 μm thickness, were post-treated by implantations of N or C + N at an energy level of 50 keV. The dose range was between 5 × 10¹⁶ and 1 × 10¹⁸ ions cm^?2. After implantation, the tribological performance of the coatings was investigated by a ball-on-disk tribometer against WC–6 wt.%Co ball under dry condition in ambient air. The wear performance of the samples was examined by a variety of characterization techniques, such as secondary electron microscopy (SEM), 3D profilometry, atomic force microscopy (AFM), and micro-Raman. The results showed that the wear performance of the samples depended strongly on the implanted elements and doses. There was slight improvement on the samples implanted with N whereas significant improvement was found on the C + N implantations. Particularly, the friction coefficient of the sample with 5 × 10¹⁷ C⁺ cm^?2 and 5 × 10¹⁷ N⁺ cm^?2 could reach 0.1. In addition, the specific wear rate of the sample was extremely low (0.85 × 10^?7 mm³/Nm), which was nearly two orders of magnitude below that of the un-implanted coating. The speculation of the mechanical and tribological analyses of the samples indicates that the improvement of the N implanted and C + N implanted TiAlSiN samples could be due to a combined effect of improved hardness, plus enhanced adhesive and cohesive strength. In addition, the improved performance of the C + N implanted samples could be explained by the formation of lubricating implanted-layer, which existed mostly in sp² C–C and C–N forms. The formation of such implanted layer could lead to a change of wear mode from strong abrasive wear to mostly adhesive wear, and result in a drop of friction coefficient and wear rate.     

Effects of carbon fiber length on the tribological properties of paper-based friction materials

Four kinds of paper-based friction materials reinforced with carbon fibers of 100, 400, 600 and 800 μm were prepared by paper-making processes. Experimental results showed that the friction materials became porous with fiber length increasing. The friction torque curves were flat except the sample with 100 μm fibers. The wear rate of the sample with 100 μm fibers was only 1.40×10⁻⁵ mm³/J. Tiny debris and fine scratches formed in the worn surface were the reason for excellent wear resistance of friction pairs with 100 μm fibers. The friction pairs with 400, 600 and 800 μm fibers showed typically abrasive wear and fatigue wear.     

A comparative study on the wear properties of coarse-grained Al6061 alloy and nanostructured Al6061–Al2O3 composites

Wear behavior of nanostructured Al6061 alloy and Al6061–Al₂O₃ nanocomposites produced by milling and hot consolidation were investigated. The samples were characterized by hardness test, pin-on-disk wear test, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Nanocomposites containing 3 vol% Al₂O₃ showed a maximum hardness of 235 HV and optimum wear rate of 4×10⁻³ mg/m. Increasing the amount of Al₂O₃ up to 5 vol% resulted in decrease in hardness values (∼112 HV) and a sharp rise in wear rate (∼18×10⁻³ mg/m).     

Wear characteristics of Cr3C2–NiCr and WC–Co coatings deposited by LPG fueled HVOF

Wear behavior of the HVOF deposited Cr₃C₂–NiCr and WC–Co coatings on Fe-base steels were evaluated by the pin-on-disc mechanism. The constant normal load applied to the pin was 49 N and sliding distance was 4500 m with velocity of 1 m/s, at ambient temperature and humidity. The specific wear rate of WC–Co coating was 3 mm³/N m and Cr₃C₂–NiCr coating was 5.3 mm³/N m. SEM/EDAX and XRD techniques were used to analyze the worn out surface and wear debris. The Fe₂O₃ was identified as the major phase in the wear debris. The wear mechanism is mild adhesive wear in nature.     

Improved wear resistance in alumina-PTFE nanocomposites with irregular shaped nanoparticles

Past studies with PTFE nanocomposites showed up to 600× improvements in wear resistance over unfilled PTFE with the addition of Al₂O₃ nanoparticles. Irregular shaped nanoparticles are used in this study to increase the mechanical entanglement of PTFE fibrils with the filler. The tribological properties of 1, 2, 5 and 10 wt.% filled samples are evaluated under a normal pressure and sliding speed of 6.3 MPa and 50.8 mm/s, respectively. The wear resistance was found to improve 3000× over unfilled PTFE with the addition of 1 wt.% nanoparticles. The 5 wt.% sample had the lowest steady state wear rate of K = 1.3 × 10⁻⁷ mm³/N m and the lowest steady friction coefficient with μ = 0.21.     

1-N-alkyl -3-methylimidazolium ionic liquids as neat lubricants and lubricant additives in steel–aluminium contacts

The influence of the alkyl chain length and of the anion on the lubricating ability has been studied for the room-temperature ionic liquids (IL) 1-n-alkyl-3-methylimidazolium X⁻ [X = PF₆; n = 6 (L-P106). X = BF₄; n = 2 (L102), 6 (L106), 8 (L108). X = CF₃SO₃; n = 2 (L-T102). X = (4-CH3C6H4SO3); n = 2 (L-To102)]. Neat IL have been used for AISI 52100 steel-ASTM 2011 aluminium contacts in pin-on-disk tests under variable sliding speed. While all IL give initial friction values lower than 0.15, real-time sharp friction increments related to tribochemical processes have been observed for L102 and L-P106, at room-temperature and at 100 °C. Electronic microscopy (SEM), energy dispersive (EDS) and X-ray photoelectron (XPS) spectroscopies show that wear scar surfaces are oxidized to Al₂O₃ and wear debris contain aluminium and iron (for L102) fluorides. For L-P106, the steel surface is covered with a P-containing tribolayer. A change of anion (L-T102; L-To102) reduces friction and wear, but the lowest values are obtained by increasing the alkyl chain length (L106; L108). When the more reactive L102 and L-P106 are used as 1 wt.% base oil additives at 25 °C, tribocorrosion processes are not observed and a friction reduction (69–75% for 1 wt.% L102) and a change from severe (10⁻³ mm³ m⁻¹) to mild wear (10⁻⁴ to 10⁻⁶ mm³ m⁻¹) is obtained with respect to the neat IL. 1 wt.% IL additives also show good lubricating performance at 100 °C.     

Tribological properties of nitrogen ion implanted steel

Nitrogen ions (N⁺) with three different doses were implanted on the AISI 304 LN steel samples under high vacuum at room temperature. Dose dependent morphological and structural changes were observed in the specimen. Structural changes were triggered by formation of nitrides; irradiation induced surface segregation of carbon and deposition of amorphous carbon (a-C) by the cracking of hydrocarbons during implantation from oil diffusion pump. Morphological and structural changes were found to influence nano-mechanical and tribological properties of ion implanted surfaces. The nano-indentation hardness was found to increase to 10.26 GPa with highest N⁺ ion dose due to formation of surface nitrides and amorphous carbon. Frictional force was found to decrease with increase in N⁺ ion dose and a minimum value of 0.078 N was obtained at higher dose presumably due to the formation of amorphous graphite like phase. In addition, amorphous diamond like carbon on the implanted surface can be contributing facts for high hardness. At higher dose, both deformation induced damage and wear rate (2.4 × 10^?7 mm³/Nm) were found to be minimum.     

Triboactive materials for dry reciprocating sliding motion at ultra-high frequency

High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substituting hydraulic actuators. For this application, two novel tribometers of the same type have been designed using commercially available components for sliding motion at 40 kHz with amplitudes between 2.5 μm and 5 μm. The tribometers are equipped with means to measure amplitude, frequency, power required to keep the samples in motion and load applied. The effective motion between the two contacting bodies is monitored in each of the tribometers. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The set-ups were tested using well-known 100Cr6H (AISI 52100) samples before investigating novel, non-commercial substrates such as AlFeCrTi-alloys and tungsten carbide-based coatings as well as Magnéli-type coatings (Ti_n?2Cr₂O_2n?1 and Ti_nO_2n?1). This paper presents the principle of the ultra-high frequency tribometers and first tribological quantities of materials and coatings tested up to and above 10¹¹ cycles. Very low wear rates in the range 10^?8 mm³/Nm down to 10^?10 mm³/Nm were determined under dry oscillation in air.     

Determination of haloperidol drug in ampoules and in urine samples using a potentiometric modified carbon paste electrode

A modified carbon paste electrode for haloperidol drug based on haloperidol-phosphomolybdate (HP-PM) as an ion-exchanger dissolved in plasticizer DBP and its potentiometric characteristics were discussed. The electrode exhibited a good Nernstian slope of 56.9 ± 0.3 mV/decade with a linear concentration range from 3.2 × 10⁻⁶ to 1.0 × 10⁻² M for the haloperidol ion. The limit of detection (LOD) was 1.5 × 10⁻⁶ M. It had response time of 5–8 seconds (s), useable in pH range of 6.2–8.6 and temperature of 20–60 °C. The electrode shows clear discrimination of haloperidol drug from several inorganic ions, sugars and some common drug excipients. The sensor was applied for determination of haloperidol drug in urine and in pharmaceutical formulations using potentiometric determination, standard addition and the calibration curve methods. The results are satisfactory with excellent percentage recovery comparable or better than those obtained by other routine methods.     

Synthesis of boride coatings on steel using plasma transferred arc (PTA) process and its wear performance

Boriding of the surface of a tool steel using boron powder and the plasma transferred arc process was investigated. It was shown that this method is an easy and effective technique in producing uniform alloyed layers with a thickness of about 1.5 mm and a hardness between 1000 and 1300 HV.The microstructure of the borided surfaces consists of primary Fe₂B-type borides and a eutectic mixture of borides and martensite. Some cracks are observed in the eutectic regions but they do not seem to critically affect the behaviour of the coatings in sliding wear.The wear rate of pin on disc tests is primarily affected by the applied load and it lies between 10⁻⁵ mm³/m for low loads and 10⁻² mm³/m for high loads. Two distinct regimes of mild and severe wear are obtained separated by a critical load. Mild wear is due to the load supporting effect of borides and severe wear is due to their breakage above a critical load. The wear rate is not significantly affected by the sliding velocity and is consistent with the friction coefficient.The friction coefficient varies from 0.13 to 0.23 and depends strongly on the oxidation status of the wear track. The sliding velocity affects the sliding distance where the coefficient of friction reaches equilibrium.     

Comparison of self-mated hardmetal coatings under dry sliding conditions up to 600 °C

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr)₂C-7%Ni, Cr₃C₂-25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 °C. For the coatings sliding speeds were varied in the range 0.1–1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC- and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10^?6 mm³/Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.     

Study on tribological properties of UHMWPE irradiated by electron beam with TMPTMA and TPGDA as crosslinking agents

Trimethylolpropane trimethacrylate (TMPTMA) and tripropylene glycol diacrylate (TPGDA) used as crosslinking agents were blended with ultra-high molecular weight polyethylene (UHMWPE or UPE) in alcohol, respectively. Then UPE plates were made by compression molding and electron beam (EB) irradiation crosslinking methods. FTIR, Soxhlet extractor, DSC, Wear tester and SEM were used for the characterization of all specimens. FTIR analyses show that trans-vinylene (965 cm^?1) absorption increases in all specimens and the >C=C< stretching absorption decreases after irradiation. Soxhlet experiments reveal that gel fraction increases with the increasing dose. DSC results indicate that X_c of all the irradiated UPEs are higher than that of unirradiated UPEs because of the free radical and small molecular which can promote the crystallization. Wear rate of 100 kGy 1%TMPTMA/UPE and 1%TPGDA/UPE are 1.89×10^?7 mm³/(N m) and 4.28×10^?7 mm³/(N m), about 44.2% and 100% of that of 100 kGy UPE, respectively, illustrating that TMPTMA is beneficial to reduce the wear rate of UPE and TPGDA almost has no effect to reduce the wear rate of UPE before 100 kGy. SEMs of irradiated specimens are more smooth than that of unirradiated specimens. These can give some advice to improve tribological properties of UPE used in the friction field.     

The lubrication of poly(etheretherketone) by an aqueous solution of nattokinase

Poly(etheretherketone) (PEEK) is a high strength and high temperature engineering polymer. However, its tribological performance is not very good in its pure form unless fillers or fibers are added to form composites. As polymers are often used for applications where traditional oil based lubrication may become an issue, water-based lubrication is desirable. This paper explores the lubrication performance of a natural fibrinolytic enzyme, nattokinase, found in fermented soybean (natto) in the aqueous solution. Pins of PEEK were slid against a steel disk in a pin-on-disk tester with the aqueous lubrication. The counterface disk material was a tool steel (R_a=0.37 μm). Tests were conducted at a rotational speed of 100 rpm and a normal load of 80 N. For comparison, tests were also conducted in NaCl solution. Nattokinase aqueous solution provides a coefficient of friction of 0.2 between PEEK and steel as compared to 0.3–0.35 for dry condition. The specific wear rates of PEEK for dry, deionized water, NaCl solution and aqueous nattokinase solution conditions were 10.5×10^?6, 51.6×10^?6, 228×10^?6 and 8.8×10^?6 mm³/N m, respectively. The fibrinolytic nattokinase enzyme provides lubricity with alkalinity reducing corrosion and eventually reducing wear.     

Wear of aligned silicon nitride under dry sliding conditions

The wear behaviour of textured silicon nitride (Si₃N₄) ceramics with aligned microstructures was analyzed under abrasive wear conditions. Dry reciprocating self-mated ball-on-flat wear tests were performed to study the influence of different microstructural plane/orientation combinations on the Si₃N₄ tribological behaviour. Textured materials showed superior wear resistance than non-textured reference Si₃N₄ for the whole range of loads and contact pressures, 5–50 N and 1.7–3.6 GPa, respectively, with an increase of about 70% for the maximum applied load. Within textured materials, the plane perpendicular to the extruding direction exhibited a 50% higher wear resistance (4 × 10^?5 mm³ N^?1 m^?1) than the parallel plane where the elongated grains were aligned. The severe wear process involved debonding, fracture and debris formation mechanisms. The progress of this sequence depended on the particular microstructure of each plane/orientation combination. A relationship between abrasive wear resistance and selected microstructural parameters has been established.     

Hardness,friction and wear studies on hydrogen peroxide treated bovine teeth

A possible problem with peroxide based tooth whitening is the loss of tooth hardness and higher susceptibility to enamel surface wear. This study focussed on the effects of acidic and neutral hydrogen peroxide solutions (6 and 30% w/v) on hardness, friction and wear of bovine enamel. The experiments showed that treatments with neutral peroxide reduced wear and the loss of enamel hardness up to 2–3 times. In addition, further investigation on remineralisation with amorphous calcium phosphate showed an increase in hardness after treatment. Friction coefficients of teeth against steel varied between 0.25 and 0.7, and wear coefficients ranged between ≈10⁻⁶ and 10⁻⁷ mm³/N m. From this study, it is possible to explain the wear behaviour of HP treated enamel with changes in hardness.