查看更多>>摘要：Owing to the geometric errors, preload of ball screws usually exhibits a two-stage degrading characteristic during operation, which is taken as the running-in stage (the first stage) and steady wear stage (the second stage), respectively. While existing researches were mainly focused on the steady wear stage, no references can be found in modelling the preload degradation during the running-in stage. Therefore, we proposed a two-stage model to compute the wear volume and preload degradation of ball screws. In the first stage, a new model considering macroscopic, geometric errors (the pitch errors, profile errors, ball radius errors, and waviness) was constructed to compute the wear volume. In the second stage, fractal theory was utilized to depict the wear volume from the microscopic perspective, in which both the adhesive wear and abrasive wear were considered. The predicted preload of the proposed model coincides well with the experimental results. Simulation results show that when the axial load increases from 5000 N to 7000 N, the first stage can be shortened as much as 50%. When the rotational speed increases from 600 rpm to 1000 rpm, the degradation rate of the first stage increases by 178%, and the first stage decreases by more than 50%. When the peak value of geometric errors increases from 1 μm to 1.8 μm, the first stage can be extended as much as 416%.
查看更多>>摘要：The CoCrNi medium-entropy alloy (MEA) exhibits an impressive ductility, but its low hardness (～352 HV) and poor wear resistance limit its engineering applications. In this study, a significant increase of surface hardness and enhancement of self-lubrication were achieved for the CoCrNi MEA using powder-pack boronizing. Results indicate that dual reaction layers with a total thickness of about 50 μm were formed on the surface. These two strengthened layers are mainly consisted of silicide (Ni2Si) and borides (CoB, Cr5B3). The hardness of the affected region reaches to 11-21 GPa dependence on the cross-sectional depth, being about 6 times higher than that of untreated MEA. In the deionized water condition, the friction and wear rate reductions of the boronizing treated specimen reach to about 25% and 63%, respectively. Energy Dispersive Spectrometer (EDS) and X-ray Photoelectron Spectroscopy (XPS) analysis on the wear scars showed that a silicon/boron-containing tribofilm was formed under the water environment, which reduces the friction coefficient and enhances the wear resistance. Our study demonstrates that powder-pack boronizing is a powerful way to enhance surface hardness and selflubrication properties of CoCrNi MEA.
B. GapinskiL. WojciechowskiM. PaczkowskaT. G. Mathia...
17页
查看更多>>摘要：Nowadays, the dynamic development of public transport is seen as one of the main ways to reduce exhaust emissions and, consequently, the greenhouse effect. One of the fastest-growing branches in this area is the building and evolution of tram lines. One of the conditions for the success of this transport method is the durability and reliability of the rail vehicles used. From a tribological point of view, friction behaviour and potential wear processes in the tram's rail-wheel contact is of special importance. Therefore, taking into account the specific structure of the tram wheel, the main goal of this study was to identify and characterise the wear mechanisms on the two areas most exposed: the running surface and the top surface of tyre flange. Furthermore, a detailed analysis of the surface topography of the worn surfaces of the tyres, with regard to the wear processes, was carried out. This part of the study included the measurements and analysis of the height parameters of the roughness and Abbott-Firestone curves (with their characteristics), both in accordance with the ISO 25178 standard. On this basis, it was found which parameters best characterise the evolution of the surface topography from the initial state to the worn one. As a consequence, those that have the potential to control the state of the tram wheels' tyres (mainly the level of wear) during operation are proposed.
查看更多>>摘要：In this study, the dry sliding wear behaviour of multiphase steels (MPS) was investigated with the help of a pin/ball-on-disc wear setup. The newly developed high strength and highly ductile MPS specimens consisting of various fractions of bainite, retained austenite, intercritical ferrite and pearlite, were obtained by a combination of continuous cooling for different times (0 s, 10 s, 20 s and 40 s) after austenitization followed by isothermal heat treatment at various temperatures (300℃, 350℃ and 400℃) for 10 min from a moderately high C (～0.67 wt%) - high Si (～1.71 wt%) steel. The worn-out surfaces and wear debris revealed that the primary material removal mechanism was of abrasive types. Wear scars were seen like a ploughed field-like structure. The depth of wear scars and amount of material collected at the periphery were affected by various phases and their fractions in the MPS specimens. The wear behaviour of the multiphase steels was affected by the distribution of plastic deformation due to continuous sliding of wear ball and application of loads on the surface of MPS specimens which was analysed by hardness variation of the sub-surfaces beneath the wear scars. At a particular austempering temperature, the wear volume loss and specific wear rate of the MPS specimens increased with the increase of continuous cooling time irrespective of the applied wear loads, and it was attributed to the formation of softer intercritical ferrite as well as pearlite formed due to longer continuous cooling. However, the bainitic structure formed by austempering without continuous cooling led to the highest wear resistance irrespective of the isothermal temperatures.
查看更多>>摘要：As one of the lightweight and wear-resistance metallic structural materials, cast Al-Si alloys have been widely studied in automobile and defense industries to meet the greater demands for elevated-temperature wearresistance properties. In this study, the effect of Ni content on the microstructure and wear behavior of Al-13Si-3Cu-1Mg-xNi-0.6Fe-0.6Mn alloys were investigated by thermodynamic modeling, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and ball-on-disk reciprocating sliding test. The results show that the θ-Al_2Cu and γ-Al_7Cu_4Ni phases are disappeared, while the δ-Al_3CuNi, ε-Al_3Ni, and T-Fe phases are formed with the increasing of Ni contents. The 3-D network structure is composed of α-Al matrix, eutectic Si, Q, Ni-rich, and Al_(15)(Mn, Fe)_3Si_2 phases, which leads to the best hardness and wear-resistance of the alloy with 2 wt% Ni. The fracture and debonding of excessive coarse ε-Al_3Ni phase deteriorate the wear-resistance and ductility of the 3Ni alloy. The main wear mechanisms of the tested alloys are abrasive, delamination and oxidative wear at 25℃ and convert to adhesive wear at 350℃.
查看更多>>摘要：Counterface roughness is known to affect the tribological behavior of carbon fiber reinforced PTFE. However, the effect of roughness in trace moisture environments has not yet been extensively investigated. In this study, the tribological behavior and tribofilm formation were evaluated for a carbon fiber reinforced PTFE composite sliding in a trace moisture environment against 34CrNiMo6 steel counterfaces with different roughness. Tribotests were conducted with a three-pin-on-disc tribometer at a sliding velocity of 2.2 m/s and in a nitrogen environment with moisture content controlled to 11 ppm. Generally, smoother counterfaces gave lower wear, both during running-in and steady-state. Contrarily, the coefficient of friction was only affected by roughness during running-in. Surface analysis from different stages of running-in were done to elucidate the formation of tribofilms and their different characteristics. For the rough countersurface, a loosely adhered transfer film is transitionally formed at the beginning of sliding to enable the formation of a persistent transfer film. Contrarily, for the case of a smooth countersurface, the formation of a persistent transfer film is initiated from the start. Similarly for the rough and smooth countersurface, a micrometer thick tribofilm with excellent low friction properties is observed on the PTFE composite after running-in.
查看更多>>摘要：In this experimental work the two parameter Weibull distribution statistical method is used to investigate the effect of fabrication process on the wear and hardness properties of multiwalled carbon nanotubes reinforced copper nanocomposites (MWCNTs/Cu). The MWCNTs/Cu nanocomposites are fabricated by the powder metallurgy processing route in two ways (i) MWCNTs/Cu nanocomposites without hot pressing (NHP-MWCNTs/Cu) and (ii) MWCNTs/Cu nanocomposites with hot pressing (HP-MWCNTs/Cu). The MWCNTs doping weight percentage (wt.%) include 0.0 (Pure copper), 0.5, 1.0 and 1.5. The MWCNTs/Cu nanocomposites are subjected to hardness and wear tests using micro-Vickers hardness tester and rotating type pin-on-disc tribometer, respectively. From the experimental results it is found that the MWNTs/Cu nanocomposites have higher hardness and lower wear rate than the pure Cu. Further, the HP-MWCNTs/Cu nanocomposites showed higher hardness and lower wear rate than the NHP-MWCNTs/C nanocomposites. From statistical analysis it is found that the HPMWCTs/Cu nanocomposites showed more reliable and repeatable experimental data than the NHP-MWCNTs/Cu nanocomposites. Statistical analysis showed that the effectiveness of MWCNTs doping on the wear rate of Cu is more effective at lower sliding speed. Finally, it is observed form the statistical analysis that both theoretical and experimental results of hardness and wear tests showed good correlation.
查看更多>>摘要：Characteristic of an ultrasonically generated pulsating water jet (PWJ) is a liquid column, the structure of which can be divided - in terms of the standoff distance of the nozzle z [mm] - into imaginary efficiency zones (initial, transition/main, final). This fact is caused by the flow gradually developing into individual pulses. The structure of the PWJ and, consequently, the nature of its interaction with the material depends on the values of technological parameters (standoff distance of the nozzle, fluid pressure, frequency of ultrasonic generation, length of the acoustic chamber, nozzle diameter, feed rate). A geometric parameter - the impact angle α [°], plays an important role, too. To date, no research has been conducted to investigate the effect of a changed impact angle of the ultrasonically generated PWJ on material erosion. Therefore, the subject matter of this study is to investigate the effect of modified impact angle of the PWJ (α = 90°, ±85°, ±75°, ±65°, ±55°, ±45°) on disintegration (groove depth hd [μm], mass loss Δm [g]) of the aluminum alloy EN AW 6060 with upward (+) and downward (-) stair motion of the nozzle over the material with the standoff distance of the nozzle ranging between z = 10-115 mm at the frequency of fs = 40 kHz, the pressure p = 40 MPa and the feed rate v = 2 mm/s. The experiment showed a semicircular pattern of grooves created in this way. The erosion rate under the perpendicular impact (α = 90°) was not the greatest due to development of a thicker protective layer of fluid. The PWJ downward motion showed greater disintegration capacity under all impact angles, probably due to the plowing effect.
查看更多>>摘要：Pulsed magnetic field treatment (MT) was applied to cemented carbide (WC-12Co) for enhancing its wear resistance in contact titanium alloy (TC4). Based on the magnetic response after MT, ferromagnetic Ni and Fe_3O_4 nanoparticles and nonferromagnetic Cu were selected as additives to prepare lubricating fluids. The results reveal that the wear resistance of the cemented carbide/titanium alloy contact under cutting fluid lubrication was improved by MT. Significantly, the wear resistance was further enhanced by coupling of MT and Fe_3O_4 magnetofluid. The workpiece wear volume of coupling decreased by 33.9%, and the ball wear scar decreased by 36.4% compared with that of the untreated ball in cutting fluid lubricant. The enhanced wear resistance comes from the magnetic response of Fe_3O_4 to the treated magnetic ball (remanence) and improved hardness. The adsorption of Fe_3O_4 nanoparticles onto the treated magnetic ball reduces the adhesion of TC4 and forms a titanium alloy film containing Fe_3O_4 nanoparticles. In addition, increased hardness due to magnetostriction and magnetic domain enlargement during pulsed magnetization also contributes to the enhanced wear resistance.
G. S. GehlenP. D. NeisL. Y. BarrosJ. C. Poletto...
12页
查看更多>>摘要：The present paper addresses the tribological behaviour of new eco-friendly brake friction materials with rice husk (RH). Three formulations with different RH content (0%, 6% and 12%) were developed and subjected to the SAE J2522 test procedure, plus an extra high-temperature section, through a laboratory-scaled braking tribometer. At 300℃, RH acted holding wear debris and improving wear resistance due to the formation of large contact plateaus. At 550℃, RH's organic compounds degraded, leading to a greater material fade. Formulation 6% RH outperformed the others, showing the lowest wear. In this case, the effect of the hard and temperature resistant silica outweighed the degradation of the organic compounds.
NSTL
Elsevier