Reciprocating Sliding Friction and Wear Property of Fe<Subscript>3</Subscript>Si Based Alloys Containing Cu in Water Lubrication

Fe₃Si, Fe₃Si alloys containing Cu were fabricated by arc melting followed by hot-pressing. The friction and wear behaviors of Fe₃Si based alloys with and without Cu addition against Si₃N₄ ball in water-lubrication were investigated. The friction coefficient and the wear rates of Fe₃Si based alloys decreased as the load increased. The wear rate of Fe₃Si was higher than that of AISI 304. The addition of Cu can significantly improve the friction and wear properties of Fe₃Si based alloys and substantially reduce the wear rates of Si₃N₄ ball. The wear rate of Fe₃Si–10%Cu was 2.56 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 20 N and decreased to 1.64 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear rate of Si₃N₄ ball against Fe₃Si–10%Cu was 1.41 × 10⁻⁶ mm³ N⁻¹ m⁻¹, while the wear rate of Si₃N₄ ball against AISI 304 was 5.20 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear mechanism was dominated by micro-ploughing. The combination of mechanical action (i.e., shear, smear and transference of Cu) and tribochemical reaction of Si₃N₄ with water was responsible for the improved tribological behavior of Fe₃Si alloys containing Cu under high loads.     

Tribological duality of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>

We report here on the friction behavior of fine- and coarse-grained Ti₃SiC₂ against steel and Si₃N₄ balls. Two successive friction regimes have been identified for both grain sizes and both counterparts. First, Type I regime is characterized by a relatively low (0.1–0.15) friction coefficient, and very little wear. Sliding occurs between a tribofilm on the ball and the Ti₃SiC₂ plane when against steel. Then, a Type II regime often follows, with increased friction coefficients (0.4–0.5) and significant wear. Compacted wear debris seems to act as a third body resulting in abrasion of the ball, even in the case of Si₃N₄. The transition between the two regimes occurs at different times, depending on various factors such as grain size, type of pin, and normal load applied. Some experiments under vacuum showed that the atmosphere plays also a major role. The reason for this evolution is not fully clear at that time, but its understanding is of major technological importance given the unusual good properties of this material.     

Tribological Properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/CuCrZr Composites

Al₂O₃ particles reinforced Cu–Cr–Zr alloy matrix composite was fabricated through a powder metallurgy plus hot extrusion process by using the water atomization Cu–Cr–Zr powder as raw material. The effect of aging treatment on the tribological behavior of the composite was investigated. Experimental results show that tiny coherent precipitated phases were formed in the matrix after proper aging treatment and therefore good combination properties could be obtained. The wear rates of the Al₂O₃/CuCrZr composite and its matrix alloy were obviously influenced by the aging treatment, wherein the best wear resistance was reached at the aging temperature corresponding to the highest Vickers hardness. The major reason was that the depth of plastic deformation in the subsurface region was dramatically decreased due to the improvement of mechanical properties of the matrix, and therefore adhesion induced surface materials loss could be markedly alleviated. By comparing with the SiC20 vol%/Cu composite, it is indicated that the Al₂O₃/CuCrZr composite exhibited much better wear resistance as well as higher electrical conductivity.     

Effect of Applied Load and Surface Roughness on the Tribological Properties of Ni-Based Superalloys Versus Ta<Subscript>2</Subscript>AlC/Ag or Cr<Subscript>2</Subscript>AlC/Ag Composites

The novel Ta₂AlC–20 vol.% Ag (TaAg) and Cr₂AlC–20 vol.% Ag (CrAg) composites were tribologically tested versus a Ni-based superalloy Inc718 (SA) by dry sliding at a sliding speed of 1 m/s at room temperature in air at loads from 3 N to 18 N. The TaAg composites were also tested at 8 and 18 N at 550 °C, and at a 3 N load against the SA with different surface roughnesses at 26 °C and 550 °C. At room temperatures, the coefficients of friction, μ’s, decreased from ~0.8–0.9 to ~0.3–0.4 for both the TaAg and CrAg composites as the applied normal force increased from 3 N to 8 N. Further increases in load to 18 N did not change the μ’s. The specific wear rates, sWR, increased with increased loads for the TaAg composite; they remained almost unchanged for the CrAg composite. This behavior was attributed to the formation of glaze tribofilms—similar to ones observed previously in these tribocouples at elevated temperatures and 3 N—promoted by the increased loads. Preconditioning of the SA surface by sliding against the TaAg composite at 550 °C and 8 N resulted in μ’s of <0.2 and sWR < 10⁻⁶ mm³/N-m in subsequent room temperature sliding at 3 N. Somewhat higher, but stable room temperature μ’s of ~0.3 and sWR of ~3 × 10⁻⁵ mm³/N-m were observed when the TaAg composites were slid versus a sandblasted SA surface at 500 °C and 3 N. It follows that in situ preconditioning of the tribo-surfaces is a powerful tool for improving the properties of the MAX/Ag-SA tribocouples. The relationship between sliding conditions, chemistries of tribofilms, and their properties are discussed.     

Dry and oil-lubricated sliding wear of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/BN fibrous monoliths

A high-temperature ball-on-flat tribometer was used to investigate dry and oil-lubricated friction and wear of sintered Si₃N₄ and Si₃N₄/hexagonal boron nitride (H-BN) fibrous monoliths. The friction coefficients of base Si₃N₄ flats sliding against Si₃N₄ balls were in the range of 0.6–0.8 for dry and 0.03–0.15 for lubricated sliding, and the average wear rates of Si₃N₄ were 10^–5 mm³ N^–1 m^–1 for dry sliding and 10^–10–10^–8 mm³ N ^–1m^–1 for lubricated sliding. The friction coefficients of Si₃N₄ balls against composite fibrous monoliths were 0.7 for dry sliding and 0.01–0.08 for lubricated sliding. The average specific wear rates of the pairs were of the same order as those measured for the conventional Si₃N₄ pairs. However, the fibrous monoliths, in combination with sprayed dry boron nitride, resulted in reduction in the lubricated friction coefficients of the test pairs and significant reduction in their wear rates. The most striking result of this study was that the coefficients of friction of the Si₃N₄/H-BN fibrous monolith test pair were 70–80 lower than those of either roughened or polished Si₃N₄ when tests were performed under oil-lubricated sliding conditions over long distances (up to 5000 m). The results indicated that Si₃N₄/H-BN fibrous monoliths have good wear resistance and can be used to reduce friction under lubricated sliding conditions.     

Improvement of the Oxidation and Wear Resistance of Pure Ti by Laser-Cladding Ti<Subscript>3</Subscript>Al Coating at Elevated Temperature

Ti₃Al coating was in situ synthesized successfully on pure Ti substrate by laser-cladding technology using aluminum powder as the precursor. The composition and microstructure of the prepared coating were analyzed by transmission electron microscopy, scanning electron microscopy (SEM), and X-ray diffraction technique. Thermal gravimetric analysis was used to evaluate the high-temperature oxidation resistance of the Ti₃Al coating. The friction and wear behavior was tested through sliding against Si₃N₄ ball at elevated temperature of 20, 100, 300, and 500°C. The morphologies of the worn surfaces and wear debris were also analyzed by SEM and three-dimensional non-contact surface mapping. The results show that the Ti₃Al coating with high microhardness, high-temperature oxidation resistance, and high temperature wear resistance. The pure Ti substrate is dominated by severe adhesion wear, abrasive wear, fracture, and severe plastic deformation at lower temperature, and severe adhesion wear, abrasive wear, plastic deformation, oxidation, and nitriding wear at higher temperature, whereas the Ti₃Al coating experiences only moderate abrasive and adhesive wear when sliding against the Si₃N₄ ceramic ball counterpart. In addition, the wear debris of the laser-cladding Ti₃Al coating sliding and Si₃N₄ friction pairs are much smaller than that of pure Ti substrate and Si₃N₄ friction pairs at elevated temperature.     

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 characteristics of polycrystalline Magnéli-type titanium dioxides

The results presented in this paper have clarified experimentally, that titania-based Magnéli-phases (Ti₄O₇/Ti₅O₉ and Ti₆O₁₁) with (121)-shear planes exhibit more anti-wear properties than lubricious (low-frictional) properties. The results for dry sliding indicate that the coefficients of friction lie in the range of 0.1–0.6 depending on sliding speed and ambient temperature. The COF decreased with increasing temperature (T= 22–800°C) and increasing sliding speed (υ= 1−6 m/s). The dry sliding wear rate was lowest for the Al₂O₃ at 1 m/s at 800°C with values of 1.7 × 10−8 and 6.4 × 10−8 mm³/N m, comparable to boundary/mixed lubrication, associated with a high dry frictional power loss of 30 W/mm². The running-in wear length and, more important, the wear rate decreased under oscillating sliding tests with increasing relative humidity. The contact pressure for high-/low-wear transition increased under oscillating sliding tests with increasing relative humidity. At room temperature and a relative humidity of 100% the steady-state wear rate under dry oscillating sliding for the couple Al₂O₃/Ti₄O₇–Ti₅O₉ was lower than 2 × 10−7 mm³/N m and therefore inferior to the resolution of the continuous wear measurement sensor. TEM of wear tracks from oscillating sliding revealed at room temperature a work-hardening as mechanism to explain the running-in behavior and the high wear resistance. The hydroxylation of titania surfaces favours the high-/low-wear transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tribological Property of Ni<Subscript>3</Subscript>Al Matrix Composites with Addition of BaMoO<Subscript>4</Subscript>

The Ni₃Al matrix composites with addition of 10, 15, and 20 wt% BaMoO₄ were fabricated by powder metallurgy technique, and the tribological behaviors were studied from room temperature to 800 °C. It was found that BaAl₂O₄ formed during the fabrication process. The Ni₃Al composites showed poor tribological property below 400 °C, with high friction coefficients (above 0.6) and wear rates (above 10⁻⁴ mm³/Nm). However, the composites exhibited excellent self-lubricating and anti-wear properties at higher temperatures, and the composite with addition of 15 wt% BaMoO₄ had the lowest wear rate (1.10 × 10⁻⁵ mm³/Nm) and friction coefficient (0.26). In addition, the results also indicated that BaAl₂O₄ for the Ni₃Al composites did not exhibit lubricating property from room temperature to 800 °C.     

Friction and wear of Y-TZP and Y-TZP-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics in high-speed sliding on steel

The processes of wear of tetragonal zirconia-based ceramics partially stabilized with yttrium oxide (Y-TZP) are studied during dry high-speed sliding in pin-on-disk pairs at sliding velocities up to 47 m/s. It is shown that these wear tests produce tribolayers of intricate composition on the surface of the Y-TZP and Y-TZP-Al₂O₃ ceramic materials, inducing nonmonotonous wear-rate changes. The normal wear changes into disastrous highly intensive wear at the first stage when the sliding accelerates (from 0.1 to 4 m/s). At the second stage (in the velocity range from 6 to 47 m/s) the wear rate drops almost to its initial value, typical of slow sliding velocities (0.1 m/s). In this velocity range, the friction of the Y-TZP and Y-TZP-Al₂O₃ ceramics is almost wearless.     

Tribological Performance of Fe<Subscript>67</Subscript>B<Subscript>33</Subscript> Alloy Prepared by a Self-Propagating High-Temperature Synthesis Technique

A bulk Fe₆₇B₃₃ alloy was prepared by a self-propagating high-temperature synthesis technique that is convenient, low in cost, and capable of being scaled up for tailoring the bulk materials. The Fe₆₇B₃₃ alloy is composed of dendrites with the t-Fe₂B phase and eutectic matrix with the α-Fe and t-Fe₂B phases. The content of the dendrite t-Fe₂B is above 80 vol.%. The compressive fractured strength and Vickers microhardness are 3400 MPa and 12.4 GPa, respectively. The tribological performance of the Fe₆₇B₃₃ alloy is investigated under dry sliding and water lubricant against Si₃N₄ ceramic ball. The wear rates of the Fe₆₇B₃₃ alloy are of the magnitude of 10⁻⁵ to 10⁻⁴ mm³/m under water lubricant. It is lower than that of the Fe₆₇B₃₃ alloy under dry sliding (10⁻⁴ mm³/m). But both the friction coefficients are almost identical. Oxide layers form in both environments via different tribochemical mechanisms, which led to significant differences in wear behavior.     

Effect of Fluoride Content on Friction and Wear Performance of Ni<Subscript>3</Subscript>Al Matrix High-Temperature Self-Lubricating Composites

The self-lubricating composites Ni₃Al–BaF₂–CaF₂–Ag–Cr, which have varying fluoride contents, were fabricated by the powder metallurgy technique. The effect of fluoride content on the mechanical and tribological properties of the composites was investigated. The results showed that an optimal fluoride content and a balance between lubricity and mechanical strength were obtained. The Ni₃Al–6.2BaF₂–3.8CaF₂–12.5Ag–10Cr composite showed the best friction coefficients (0.29–0.38) and wear rates (4.2 × 10⁻⁵–2.19 × 10⁻⁴ mm³ N⁻¹ m⁻¹) at a wide temperature range (room temperature to 800°C). Fluorides exhibited a good reduced friction performance at 400 and 600°C. However, at 800°C, the formation of BaCrO₄ on the worn surface due to the tribo-chemical reaction at high temperatures provided an excellent lubricating property.     

Tribological Properties of a Nano-Eutectic Fe<Subscript>1.87</Subscript>C<Subscript>0.13</Subscript> Alloy Under Water Environment

Tribological properties of a nano-eutectic Fe_1.87C_0.13 alloy were investigated under distilled-water lubrication against AISI52100 steel ball for various applied loads and sliding speeds. For comparison, the tribological behavior of annealed coarse-grained Fe_1.87C_0.13 alloy was also examined under the same testing conditions. Worn surfaces of both alloys were analyzed by using a scanning electron microscope (SEM). The wear rate of nano-eutectic Fe_1.87C_0.13 alloy was on the order of 10⁻⁵ mm³/m. The wear rate of nano-eutectic Fe_1.87C_0.13 alloy was higher than that of annealed Fe_1.87C_0.13 alloy at lower load, but lower under higher load. The friction coefficients of the two alloys were similar and exhibited a slight increase with increasing sliding speed, but a small decrease with increasing applied load. The wear mechanism of the nano-eutectic Fe_1.87C_0.13 alloy was transformed from plowing and corrosion wear to slight fatigue cracking with increasing applied load, whereas that of the annealed coarse-grained Fe_1.87C_0.13 alloy was transformed from plowing and corrosion wear to severe fatigue flaking.     

Sliding friction and wear performance of Ti6Al4V in the presence of surface-capped copper nanoclusters lubricant

The friction and wear properties of Ti₆Al₄V sliding against AISI52100 steel ball under different lubricative media of surface-capped copper nanoclusters lubricant—Cu nanoparticles capped with O,O′-di-n-octyldithiophosphate (Cu-DTP), rapeseed oil and rapeseed oil containing 1 wt% Cu-DTP was evaluated using an Optimol SRV oscillating friction and wear tester. The wear mechanism was examined using scanning electron microscopy (SEM) and X-ray photoelectron spectrosmeter (XPS). Results indicate that Cu-DTP can act as the best lubricant for Ti₆Al₄V as compared with rapeseed oil and rapeseed oil containing 1 wt% Cu-DTP. The applied load and sliding frequency obviously affected the friction and wear behavior of Ti₆Al₄V under Cu-DTP lubricating. The frictional experiment of the Ti₆Al₄V sliding against AISI52100 cannot continue under the lubricating condition of rapeseed oil or rapeseed oil containing 1 wt% Cu-DTP when the applied load are over 100 N. Surprisingly, the frictional experiment of Ti₆Al₄V sliding against AISI52100 steel can continue at the applied load of 450 N under Cu-DTP lubricating. The tribochemical reaction film containing S and P is responsible for the good wear resistance and friction reduction of Ti₆Al₄V under Cu-DTP at the low applied load. However, a conjunct effect of Cu nanoparticle deposited film and tribochemical reaction film containing S and P contributes to the good tribological properties of Ti₆Al₄V under Cu-DTP at the high-applied load.     

Mechanical properties and tribological behavior of ZrO<Subscript>2</Subscript> thin films deposited on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

A silane coupling reagent (3-mercaptopropyl)trimethoxysilane (abridged as MPTS) was self-assembled on a single-crystal Si substrate to form a two-dimensional organic monolayer (MPTS-SAM). The terminal –SH group in the MPTS-SAM film was in-situ oxidized to –SO₃H group to endow the film with good chemisorption ability. Then ZrO₂ thin films were deposited on the oxidized MPTS-SAM by way of the enhanced hydrolysis of aqueous zirconium sulfate (Zr(SO₄)₂·4H₂O) in the presence of aqueous HCl at 50 °C, making use of the chemisorption ability of the –SO₃H group. The thickness of the ZrO₂ films was determined with an ellipsometer, while their morphologies and corresponding friction forces were analyzed by means of atomic force microscopy. The hardness and elastic modulus of the ZrO₂ thin films were determined on a Nanoindentation II (MET) instrument. The macro-friction and wear behaviors of the ZrO₂ films sliding against an AISI-52100 steel ball were examined on a unidirectional friction and wear tester and the worn surface morphologies observed on a scanning electron microscope (SEM). As the results, the as-deposited ZrO₂ thin film at a deposition duration of 100 h is about 100 nm thick, it decreases to 48 nm after annealing at 500 °C and further decreases to 45 nm after heating at 800 °C. The as-deposited ZrO₂ film is relatively rougher, with the rms to be about 1.0 nm, while the ZrO₂ thin films heated at 500 and 800 °C have surface roughness rms of 0.76 nm and 0.68 nm, respectively. The ZrO₂ film annealed at 800 °C has a high hardness to elastic modulus (H/E) ratio (0.062) as compared to the as-deposited ZrO₂ film and the film annealed at 500 °C. Both the two annealed ZrO₂ films show excellent wear-resistance as they slide against AISI-52100 steel at a normal load below 2.0 N, while the one annealed at 800 °C has better wear-resistance. The differences in the friction and wear behaviors of the as-deposited ZrO₂ film, the ZrO₂ film annealed at 500 °C and that annealed at 800 °C are attributed to their different micro structures and compositions. Since the ZrO₂ films was well adhered to the underlying MPTS-SAM, it might find promising application in the surface-protection of single crystal Si and SiC subject to sliding at small normal load in microelectromechanical systems (MEMS).     

High Wear Resistance of Magnetron Sputtered Cr<Subscript>80</Subscript>Si<Subscript>20</Subscript>N Nanocomposite Coatings: Almost Independent of Hardness

Hardness has been popularly considered as an essential factor defining the wear resistance of hard coatings. Here, we report magnetron sputtered Cr₈₀Si₂₀N nanocomposite coatings, of widely varied packing densities, that exhibited identical specific wear rates, while the hardness changed over a wide range (from ~12 to ~36 GPa). All the Cr₈₀Si₂₀N coatings were free of extended and uninterrupted columnar boundaries, and retained low specific wear rates in the ball-on-plate sliding tests against Al₂O₃ counterpart with a normal load of 5 N (less than 3.0?×?10^?16 m³/N m under ambient condition and less than 2.0?×?10^?15 m³/N m under 3.5 wt% NaCl solution, respectively). Post examination reveals extensive interruption or termination of cracks in the wear tracks of the under-dense coatings, indicative of extrinsic toughening mechanisms by effective relief of local contact stress. Our results suggest that a critical role of toughening rather than hardening, played in enhancing the wear resistance of hard coatings, and thus would pave a way to develop highly wear-resistant coatings with a low hardness.     

Tribological Behavior of Ti3AlC2 Against SiC at Ambient and Elevated Temperatures

In this paper, we reported the tribological behavior of Ti₃AlC₂ disk sliding against SiC ball from room temperature (RT) to 1,000 °C. The tribological properties are highly dependent of testing temperature. At RT, the coefficient of friction (CoF) is as low as 0.34 in the steady state, but the wear rate is relative high (4.26 × 10^?4 mm³/Nm). At 200 and 400 °C, the CoF is as high as 1.21, and the wear rates are very high, about on the order of 10^?3 mm³/Nm. From 600 to 1,000 °C, however, Ti₃AlC₂ exhibits quite low wear rate on the order of 10^?6 mm³/Nm and relative moderate CoF, 0.60–0.80. The compacted continuous oxide layer at 600 °C and above might be responsible for the outstanding wear resistance.     

Reciprocating friction and wear behavior of Ti3AlC2 and Ti3AlC2/Al2O3 composites against AISI52100 bearing steel

In this work, the dry sliding friction and wear properties of Ti₃AlC₂ and Ti₃AlC₂/Al₂O₃ composites against AISI52100 steel ball were investigated using a reciprocating ball on flat configuration under different normal loads. The results indicated that the friction/wear processes of both Ti₃AlC₂ and the composites against AISI52100 steel experienced two different stages with an abrupt transition between them under all test conditions. The first stage was characterized by low coefficient of friction (μ) and neglectable wear rate. While the second stage was of much higher wear rate and μ. When the transition occurred, μ increased dramatically accompanied with formation of a mass of debris. In Ti₃AlC₂, the main wear mechanisms during the first stage involved surface materials transfer and oxidation accompanied with subsurface damages by grains kinking, delamination as well as transgranular and intergranular cracks. Accumulating of such contact damages under repeated sliding contact finally leaded to surface and subsurface microfracture of Ti₃AlC₂. Then microfracture controlled severe wear started. Incorporation of Al₂O₃ in Ti₃AlC₂ not only improved wear resistance of Ti₃AlC₂ but also extended the first mild friction/wear stage, because Al₂O₃ particles borne load and restrained large-scale deformation and microfracture of Ti₃AlC_2.     

Further investigation on the tribological behavior of Al2O3–20Ag20CaF2 composite at 650°C

The friction and wear behaviors of the self‐lubricating Al₂O₃–20Ag20CaF₂ disk against an Al₂O₃ pin pair have been investigated over a broad load range from 1 to 30 N and sliding velocities from 0.084 to 1 m/s at 650^°C. Four typical wear modes have been identified and the wear mode map was constructed to illustrate the influence of load and speed on the friction coefficient and wear rate. The results showed the effective self‐lubricating region (II) (continuous lubricating film) is almost independent of sliding speed, and mainly dependent on the load. It is suggested that the plastic deformation and plastic flow during sliding play an important role in the formation of the self‐lubricating film on the sliding surface. Furthermore, the worn surface in the region (II) (continuous lubricating film) was found to be much softer than the original surface and the distribution of Vickers hardness became more uniform due to the presence of the lubricating film on the worn surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Speed and Atmosphere Influences on Nanotribological Properties of NbSe<Subscript>2</Subscript>

Nanotribological properties of NbSe₂ are studied using an atomic friction force microscope. The friction force is measured as a function of normal load and scan speeds ranging from 10 nm s⁻¹ to 40 μm s⁻¹ under two atmospheres (air and argon). At low speed, no effect of atmosphere is noticed and a linear relationship between the friction and normal forces is observed leading to a friction coefficient close to 0.02 for both atmospheres. At high speed, the tip/surface contact obeys the JKR theory and the tribological properties are atmosphere dependent: the shear stress measured in air environment is three times lower than the one measured under argon atmosphere. A special attention is paid to interpret these results through numerical data obtained from a simple athermal model based on Tomlinson approach.