Friction and wear properties of αFeSi2–Si alloy,ReSi1.8 and MoSi2 in ethyl alcohol

In this study, Fe–X at% Si alloy (X=70.5, 80.0 and 96.0), Re–64.3 at% Si and Mo–66.7 at% Si disk specimens were prepared by spark plasma sintering, and their friction and wear properties were investigated when they were slid against Si₃N₄ ball specimens in ethyl alcohol. The friction and wear properties of Si ingots were also examined. Fe–70.5 at% Si, Fe–80.0 at% Si, Fe–96.0 at% Si and Re–64.3 at% Si disk specimens exhibited friction coefficients as low as 0.15. It is considered that the low friction of the Fe–70.5 at% Si, Fe–80.5 at% Si and Fe–96.0 at% Si disk specimens was due to the formation of low friction silicon alkoxide and polyoxysilane on the worn surfaces of the disk specimens and the paired ball specimens. Re–64.3 at% Si disk specimens exhibited the highest microvickers hardness of all the disk specimens prepared in this study. In addition, the microvickers hardness of the Fe–X at% Si (X=70.5, 80.0, 96.0 and 100) disk specimen increased with increasing the Si content. Moreover, it was difficult to obtain dense Fe–90.0 at% Si disk specimens by sintering the annealed and crushed Fe–90.0 at% Si powder. However, dense Fe–96.0 at% Si disk specimens could be obtained by sintering the Fe–90.0 at% Si powder at 1403 K.     

A force-matching method for quantitative hardness measurements by atomic force microscopy with diamond-tipped sapphire cantilevers

We present a new method to improve the accuracy of force application and hardness measurements in hard surfaces by using low-force (<50 μN) nanoindentation technique with a cube-corner diamond tip mounted on an atomic force microscopy (AFM) sapphire cantilever. A force calibration procedure based on the force-matching method, which explicitly includes the tip geometry and the tip-substrate deformation during calibration, is proposed. A computer algorithm to automate this calibration procedure is also made available. The proposed methodology is verified experimentally by conducting AFM nanoindentations on fused quartz, Si(1 0 0) and a 100-nm-thick film of gold deposited on Si(1 0 0). Comparison of experimental results with finite element simulations and literature data yields excellent agreement. In particular, hardness measurements using AFM nanoindentation in fused quartz show a systematic error less than 2% when applying the force-matching method, as opposed to 37% with the standard protocol. Furthermore, the residual impressions left in the different substrates are examined in detail using non-contact AFM imaging with the same diamond probe. The uncertainty of method to measure the projected area of contact at maximum force due to elastic recovery effects is also discussed.     

Extremely low coefficient of friction of diamond sliding against Ag thin films on Si(1 1 1) surface under ultrahigh vacuum condition

The tribological properties of a diamond (1 1 1) pin slid on subnanometer thick Ag films, which were deposited on a cleaned Si(1 1 1) substrate, were studied using a pin-on-plate tribometer. The preparation of Ag ultrathin films and frictional experiments were performed in an ultrahigh vacuum (UHV) chamber at a pressure of 10⁻⁸ Pa. The frictional experiments were carried out at a sliding speed of 0.1 mm/s and at a normal load of 250 mN. An extremely low coefficient of friction, less than 0.01, was obtained when the pin was slid on Ag films, whose thicknesses were 1 and 2.6 monolayer (ML) under reciprocal motion. The minimum coefficient of friction was less than 0.004 for Ag 1 ML film. After the extremely low coefficient of friction was obtained, Ag remained on the worn track without any transfer to the diamond pin, as confirmed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS).The mechanisms of extremely low coefficients of friction are discussed in terms of the chemical bonding force between atoms of the topmost layers, and Ag coverage on the Si surface.     

Tribological and electrical properties of nanocrystalline Cu films deposited by DC magnetron sputtering with varying temperature

Cu films were deposited on Si substrates by direct current (DC) magnetron sputtering at three different substrate temperatures such as room temperature (RT), 100 °C and 200 °C. Possible mechanisms for substrate temperature dependent microstructure evolution in Cu films are discussed in this paper. Enhanced mechanical properties such as high hardness, high elastic modulus, low friction coefficient and high wear resistance of the films were obtained at deposition temperature of 100 °C. However, high friction coefficient as well as high wear rate was measured in films deposited at room temperature and 200 °C.     

Electrogenerated chemical polishing of copper

Stress free polishing method is preferred for a damage free surface of copper with ultra-flatness and ultra-smoothness. Such a surface offers a perfect substrate for integrated circuits and micro-electromechanical systems fabrication. A new polishing method, called electrogenerated chemical polishing (EGCP), is proposed based on the principle of the scanning electrochemical microscope (SECM) and the diffusion controlled chemical reaction. Roughness of a Cu surface is reduced from 100.5 nm to 3.6 nm by the proposed method. To demonstrate the planarization capability of this new method, a patterned Cu surface with an array of micro-columns is planarized with a peak-valley (PV) value from 4.7 μm to 0.059 μm.     

Cavitation erosion of Fe–Mn–Si–Cr shape memory alloys

Cavitation erosion tests of three Fe–Mn–Si–Cr shape memory alloys were carried out at speed 34 and 45 m/s using a rotating disc rig, and their cavitation damage has been investigated by comparison with a referring 13Cr–5Ni–Mo stainless steel used for hydraulic turbine vanes. The research results proved that the cavitation erosion of the Fe–Mn–Si–Cr shape memory alloys is a failure of low cycle fatigue and fracture propagates along grain boundaries. After 48 h cavitation erosion the cumulative mass losses of the studied alloys at speed 45 m/s are more than theirs at speed 34 m/s; however, the effect of velocity on cavitation damage of the Fe–Mn–Si–Cr alloys is much lower than that of 13Cr–5Ni–Mo stainless steel. The cumulative mass loss of the 13Cr–5Ni–Mo stainless steel are 26.3 mg at speed 45 m/s and 3.2 mg at speed 34 m/s, and the mass losses of the Fe–Mn–Si–Cr alloys are within the range of 3.6–7.3 mg at speed 45 m/s and 2.0–4.1 mg at speed 34 m/s. The surface elasticity of the Fe–Mn–Si–Cr shape memory alloys is better than that of the 13Cr–5Ni–Mo stainless steel, and the effect of surface elasticity on cavitation damage increases with velocity. The excellent surface elasticity of the cavitation-induced hexagonal closed-packed (h.c.p.) martensite plays a key role in contribution of phase transformation to the cavitation erosion resistance of the Fe–Mn–Si–Cr shape memory alloys. The cavitation damage of the studied alloys at speed 45 m/s mainly depends on their surface elasticity, and the variation of 48 h cumulative mass loss (Δm) as a function of the elastic depth (h_e) can be expressed as Δm=2.695+[1371.94/(4(h_e−46.83)²+12.751)] with a correlation factor of 0.99345.     

Sliding wear behavior of hardfacing alloys in a pressurized water environment

In this study, sliding wear behavior of newly developed Fe-base Co-free hardfacing alloy (Fe–Cr–C–Si) was investigated and compared to that of Stellite 6 and Fe-base NOREM 02 in the temperatures ranging from 300 to 575 K under a contact stress of 103 MPa (15 ksi) in pressurized water. The weight loss of Fe–Cr–C–Si was equivalent to that of Stellite 6 over all temperatures range in 100-cycle wear test. The weight loss of Fe–Cr–C–Si 1000-cycle wear test increased almost linearly with increasing temperature up to 575 K. The weight loss of NOREM 02 was nearly equivalent to that of Stellite 6 below 475 K, however, galling occurred above 475 K in 100-cycle wear test. It was also found that the lubrication effect of pressurized water on the sliding wear behavior of the alloys was negligible under the present test conditions.     

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.     

Sliding friction induced atom diffusion in the deformation layer of 0.45% C steel rubbed against Tin alloy

Evolution of microstructure and compositions in worn surface and subsurface of 45 (0.45 mass% carbon) steel disc slid against tin-alloy-pin was analyzed by SEM, TEM and SIMS. The mechanical alloying layer and plastic deformation layer were formed in the sliding friction-induced deformation layer (SFIDL) of 45 steel. Ultra-refine and nano grains were detected in the worn surface layer. Elements of Sn, Cu and Sb, originated from the mating tin-alloy-pin, with diffusion depth of 35 μm, 11 μm and 4 μm, respectively, were detected in its SFIDL. Mechanisms accelerating atom diffusion in SFIDL were subsequently propounded.     

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.     

Fabrication of a resin-bonded ultra-fine diamond abrasive polishing tool by electrophoretic co-deposition for SiC processing

A resin-bonded ultra-fine diamond abrasive polishing tool is fabricated by electrophoretic co-deposition (EPcD), and the processing performance of the tool is evaluated in this study. The dispersion stability of suspensions is characterized by a laser particle size analyzer and settlement ratio. The cathodic EPcD of composite powder is realized by adding Al³⁺ into the suspension. The sintering temperature of composite coatings is determined by differential thermal analysis/thermogravimetry. The surface morphology of the composite coating is observed under a confocal microscope. Results show that uniform, dense, and smooth coatings with diamond and resin particles distributed homogeneously are obtained from the steel substrate. A large (Φ150 mm) polishing tool with a 20 μm-thick coating is successfully prepared using the above process. A smooth mirror surface of SiC wafer with a nanoscale roughness (4.3 nm) is achieved after processing with the ultra-fine diamond abrasive polishing tool.     

On the film thickness dependence of shear strengths in sliding,boundary-layer friction

The density functional theory calculated pressure-dependent shear strength S of a four-layer slab of KCl on a Fe(1 0 0) substrate is compared to previous calculations for a bilayer slab to gauge the effect of film thickness on the shear properties of the film. It is found that the shear strength varies with pressure as S = S₀ + αP, where P is the contact pressure. The resulting calculated values for the four-layer slab are S₀〈1 0〉 = 62 ± 15 and S₀〈1 1〉 = 65 ± 11 MPa while α〈1 0〉 and α〈1 1〉 are 0.06 ± 0.01. The values are very close to those calculated for the bilayer slab of S₀〈1 0〉 = 64 ± 9 and S₀〈1 1〉 =69 ± 8 MPa and α〈1 0〉 and α〈1 1〉 of 0.05 ± 0.01, and in reasonable agreement with the experiment values. These results suggest that the thickness of the film does not have a profound effect on the shear properties.     

Cutting forces,tool wear and surface finish in high speed diamond machining

We have investigated the cutting forces, the tool wear and the surface finish obtained in high speed diamond turning and milling of OFHC copper, brass CuZn39Pb3, aluminum AlMg5, and electroless nickel. In face turning experiments with constant material removal rate the cutting forces were recorded as a function of cutting speed between v_c = 150 m/min and 4500 m/min revealing a transition to adiabatic shearing which is supported by FEM simulations of the cutting process. Fly-cutting experiments carried out at low (v_c = 380 m/min) and at high cutting speed (v_c = 3800 m/min) showed that the rate of abrasive wear of the cutting edge is significantly higher at ordinary cutting speed than at high cutting speed in contrast to the experience made in conventional machining. Furthermore, it was found that the rate of chemically induced tool wear in diamond milling of steel is decreasing with decreasing tool engagement time per revolution. High speed diamond machining may also yield an improved surface roughness which was confirmed by comparing the step heights at grain boundaries obtained in diamond milling of OFHC copper and brass CuZn39Pb3 at low (v_c = 100 m/min) and high cutting speed (v_c = 2000 m/min). Thus, high speed diamond machining offers several advantages, let alone a major reduction of machining time.     

Structural and photoluminescence studies of rutile TiO2 nanorods prepared by chemical bath deposition method on Si substrates at different pH values

The effects of pH on the structural, morphological and optical properties of TiO₂ nanorods were investigated. Nanorods were fabricated on p-type (1 1 1)-oriented silicon substrates and all substrates were seeded with a TiO₂ seed layer synthesized with a radio-frequency reactive magnetron sputtering system (the TiO₂ seed layer was also examined in this research). Chemical bath deposition (CBD) was performed to grow rutile TiO₂ nanorods on Si substrate at various pH values (0.5, 0.7 and 0.9). Raman spectroscopy, X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) analyses showed the tetragonal rutile structure of the synthesized TiO₂ nanorods. Optical properties were examined photoluminescence spectroscopy, which indicated a high-intensity UV peak centered at around 390 nm for all samples compared with visible defect peaks. Experimental results showed that the TiO₂ nanorods grown at pH 0.7 exhibited the optimal structural properties. Moreover, the CBD method enabled the formation of photosensitive and high-quality rutile TiO₂ nanorods with few defects for future optoelectronic nanodevice applications.     

Characterization and tribological investigation of sol–gel ceramic films on Ti–6Al–4V

SiO₂, TiO₂, and hydroxyapatite (HA) thin films with good biocompatibility were grown on Ti–6Al–4V (coded as TC4) substrate by sol–gel and dip-coating processes from specially formulated sols, followed by annealing at 500 °C The chemical states of some typical elements in the target films were detected by means of X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM) are applied to characterize the original unworn films. The tribological properties of thin films sliding against an AISI52100 steel ball were evaluated on a reciprocating friction and wear tester. As the result, the target films composed of nano-particles ranging from 30 nm to 100 nm around were obtained. All the sol–gel ceramic films are superior in resisting wear compared with the TC4 substrate. Among all, HA film shows the best resistance while SiO₂ film shows the worst wear resistance both under higher (3 N) and lower load (1 N). TiO₂ shows good wear resistance under lower load (1 N). SEM observation of the morphologies of worn surfaces indicates that the wear of TC4 is characteristic of abrasive wear. Differently, abrasion, plastic deformation and micro-fracture dominate the wear of ceramic films. The superior friction reduction and wear resistance of HA film is greatly due to the slight plastic deformation of the film. It is supposed that the deformation of the HA film is closely related to the special arrangement of the nano-particles and microstructure. HA film is recommended for clinical application from the point of wear resistance view.     

Friction and wear behavior of laser composite surfaced aluminium with silicon carbide

The present study concerns the wear behavior of laser composite surfaced Al with SiC and Al + SiC particulates. A thin layer of SiC and Al + SiC (at a ratio of 1:1 and dispersed in alcohol) were pre-deposited (thickness of 100 μm) on an Al substrate and laser irradiated using a high power continuous wave (CW) CO₂ laser. Irradiation leads to melting of the Al substrate with a part of the pre-deposited SiC layer, intermixing and followed by rapid solidification to form the composite layer on the surface. Following laser irradiation, a detailed characterization of the composite layer was undertaken in terms of microstructure, composition and phases. Mechanical properties like microhardness and wear resistance were evaluated in detail. The microstructure of the composite layer consists of a dispersion of partially melted SiC particles in grain refined Al matrix. Part of the SiC particles are dissociated into silicon and carbon leading to formation of the Al₄C₃ phase and free Si redistributed in the Al matrix. The volume fraction of SiC is maximum at the surface and decreases with depth. The microhardness of the surface improves by two to three times as compared to that of the as-received Al. A significant improvement in wear resistance in the composite surfaced Al is observed as compared to the as-received Al. The mechanism of wear for as-received vis-à-vis laser composite surfaced Al has been proposed.     

Effect of electrical current on tribological behavior of copper-impregnated metallized carbon against a Cu–Cr–Zr alloy

A block-on-slip ring-type wear tester was used to investigate the tribological behavior of copper-impregnated metallized carbon against a Cu–Cr–Zr alloy under 2 to 6 N applied load and 0 to 20 A electrical current. The sliding speed was maintained at 25 km/h. The wear loss of copper-impregnated metallized carbon increased with greater electrical current. Under a certain applied load, the wear loss with electrical current was minimized. The tribo-layer had an apparent effect on the friction coefficient. The wear mechanisms were complex, consisting of adhesive wear, abrasive wear and arc erosion.     

Influence of surface treatment of elastomers on their frictional behaviour in sliding contact

To reduce friction of elastomer parts moving against a metal counter body in dry conditions, two different surface treatment techniques were applied on elastomer parts: laser cladding and plasma treatment at atmospheric pressure.Polyamide 11 (PA 11) based coatings were produced on thermoplastic polyurethane (TPU) substrates by laser cladding. During ball-on-disc tribotesting the effect of a PA 11 coating was identical to that of a PA 11 + 9% MoS₂ coating: friction of the TPU substrate was reduced with 40%. The incorporation of 15 wt% PTFE in the PA 11 coating resulted in a further decrease of the frictional force. A reduction of 80% of the frictional force of the TPU substrate was measured. The surface of the coatings before and after tribotesting was analysed.The plasma treatment of HNBR was done using a Plasmaspot^® to form a plasma polymerised coating based on two different types of siloxanes. A reduction of 74–80% of the initial friction coefficient was measured in two different tribotest rig configurations: ball-on-disc and disc-on-disc. The resulting wear tracks were analyzed by SEM and EDX.     

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 three nitriding treatments on tribological performance of 42CrAlMo7 steel in boundary lubrication

Evolution of friction and wear of 42CrAlMo7 steels with different nitriding processes was investigated during boundary-lubricated rolling–sliding tests. The wear behaviour of nitrided steel with a thin compound layer (produced by plasma nitriding and by gas nitriding followed by oxidation) was characterised by the early removal of the compound layer, and the wear resistance was thus, given by the underlying diffusion layer. In the case of the material with a thick compound layer (produced by gas nitriding) wear was restricted to the compound layer. In this material, at low applied load (300 N, i.e. 485 MPa of Hertzian pressure, in this work), after the removal of the external porous layer wear tended to be negligible. At high applied load (1000 N, 890 MPa), on the other hand, the wear rate became higher than that of the diffusion layer. The friction behaviour was followed by determining the λ-factor evolution during each test. For a given λ-factor, the friction coefficients at 300 N were lower than at 1000 N.