Bedoya-Zapata, A. D.Leon-Henso, H.Molina, L. F.Palacio, M....
9页
查看更多>>摘要：Three different rail grades (R260, R350HT and R400HT) were ground in a metropolitan railway using the same parameters of a standard grinding procedure. After the grinding tests, two cross sections of each rail grade were extracted to characterize the microstructure through metallography and microhardness measurements. A White Etching Layer (WEL) was found for the three rail grades. The thickness, angular distribution, and total length of the WEL varied along the rail's head depending on the rail grade. The analysis of the grinding parameters used showed that the conditions imposed involve higher pressures than those typically reported in literature. The results of this study will contribute to improve grinding procedures in the field for specific rail grades used in commercial lines.
查看更多>>摘要：Atmospheric plasma spray coatings can provide a solution for corrosion and wear resistant cylinder coating surfaces in hybrid powertrains. This article presents experimental results from a model study of metal matrix composite coating samples of chromium steel with varied ceramic content, in order to characterize the effect of hard particles and porous coating structure on friction and wear. Experiments were conducted on a highfrequency reciprocating rig with coated cast-iron cylinder segments and hard chromium coated piston ring segments. Samples were investigated under continuous and scarce lubrication conditions. A ceramic content of 35 wt% was found to be ideal in terms of friction and wear. Coatings with a higher ceramic content exhibited severe abrasive wear, whereas a ceramic content under 35 wt% allowed for increased adhesion between the ring and cylinder surfaces. A detailed investigation of focused ion beam milled sections of the coated cylinder wall segments revealed a stabilizing effect of the ceramic particles, which reduces the delamination of the coating structure.
Makowiec, Mary E.Gionta, Grace L.Bhargava, SuvratOzisik, Rahmi...
10页
查看更多>>摘要：Following numerous studies demonstrating the ability of nanostructured alpha-alumina filler to reduce the prohibitively high wear rate of polytetrafluoroethylene (PTFE) down to extremely small values (~ 10(-7) mm(3)/ Nm) well below those of conventional PTFE micro-composites, alpha-alumina filler was also shown capable, in a couple recent studies, of imparting similar performance to another fluoropolymer, perfluoroalkoxy (PFA) copolymer, which otherwise was similarly lacking wear resistance in the unfilled state. In addition to duplicating such alpha-alumina performance in PFA, in this study such an extreme wear-reducing capability has also been demonstrated using nanocarbon powder, as an example representative of several other forms of nanoscale carbon filler that like alpha-alumina had been shown capable of providing extreme resistance to PTFE. Fluorinated ethylene propylene (FEP) copolymer, whose nanocomposites have not been tribologically explored previously, was thus more fully investigated here with not only alpha-alumina and nanocarbon, but also other nanotube (CNT) and mesoporous forms of nanoscale carbon fillers. In preliminary testing, only the alpha-alumina filler indicated an ability to impart its wear-reducing capability to FEP; a wear rate of ~0.8 x 10(-6) mm(3)/Nm was observed at 2 wt% alpha-alumina concentration. While this is an impressive reduction in wear rate, it is not quite as extreme a reduction as that observed in PTFE or PFA. The transport of the extreme wear resistance of nanocarbon powder in PTFE and PFA was even more partial and incomplete in FEP, with the ~0.3 x 10(-3) mm(3)/ Nm unfilled FEP wear rate only reduced to ~10(-5) mm(3)/Nm, while the CNT and mesoporous carbon fillers were even less effective. Correspondingly, ATR-FTIR spectra from FEP wear surfaces displayed sizable peaks evident of the chelation of chemical interactions known to be associated with wear resistance for PTFE and PFA matrices only in the most wear-resistant alpha-alumina case and to a lesser extent for the nanocarbon. Finally, it is demonstrated that such fillers demonstrate such strongly beneficial effects only in polymers that otherwise lack wear resistance, and may actually be deleterious for polymers such as high density polyethylene (HDPE) already having some inherent wear resistance in their unfilled state.
查看更多>>摘要：The demand for efficient and sustainable energy is continuously increasing. Among the many technologies with great potential within this field are nanofluids. Nevertheless, there is still a considerable lack of information regarding their erosive effects on systems materials. In this research, the tribological behaviour of aqueous 1.33 wt% TiO2 nanofluid was investigated when jet-impinged with an average velocity of 0.8 m/s at flat targets of various materials (plastic, copper, rubber). The target surfaces were analysed using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and X-ray diffraction (XRD). It was found that impinging TiO2 nanofluid caused erosion of 282 g/(yr.mm(2)) for copper and 212 g/(yr.mm(2)) for plastic. In addition, a deposition of nanoparticles was found for rubber at rate of 2.7 kg/(yr.mm(2)).
查看更多>>摘要：In this study, a surface profile modification method is proposed to improve the transient Wear and Asperity Contact (WAC) performance of the water-lubricated bearing under fluid-solid-thermal coupling condition. The validated numerical model is used to demonstrate the effectiveness of the proposed profile modification method. Based on numerical calculations, it is found that the profile modification method has the potential to decrease the edge wear depth and averaged asperity contact force of water-lubricated bearings, and the optimal modification width and depth are numerically determined. Numerical results indicate that a slight increase in the wear depth of the middle part of the bearing is observed if the profile modification method is employed. Furthermore, a group of parametric studies are carried out to assess the effectiveness of the profile modification method within a wide range of design parameters and operating conditions, including radial clearance, surface roughness, external load and rotational speed. Numerical results reveal that the effectiveness of the profile modification method is closely related to the design parameters and operating conditions. Generally, a relatively large profile modification depth may not be recommended.
查看更多>>摘要：In this paper, various dry lubricants made of a polyamide (PA) matrix and two different grades of radiation modified PTFE, which are chemically bonded to the matrix by reactive melt extrusion, are examined regarding their tribological suitability and compared to a PA-PTFE reference compound with non-modified PTFE. For this purpose, a block-on-ring test rig was used under ambient conditions, where the block made of dry lubricant is sliding on a steel ring made of 16MnCr5 with constant sliding speed. Results of tribological tests on the block-on-ring test rig such as wear and friction depending on the contact pressure are presented. In addition to that, analyses of the layer formation of the lubricants on steel counterparts are shown. An essential finding of the investigations is that the mass thickness on the tribologically stressed surfaces to be lubricated with the dry lubricant is not directly related to the compound wear, but rather depends on the pressure in the steel-compound contact. Furthermore, examinations showed that an increase of pressure in the block-ring contact does not lead to an increase of the amount of dry lubricant material on the steel surface.
查看更多>>摘要：A boric acid fuel additive has shown promising results in field-tested internal combustion engines by resulting in substantial fuel consumption reductions. The present study evaluated the lubricating, tribofilm forming, and wear protective abilities of the fuel additive when mixed into four fuels; ethanol (E85), gasoline, diesel and marine gas oil (MGO). A reciprocating ball-on-disc setup was used for the test, to mimic the conditions of components that run lubricated by the fuel, such as fuel pumps and fuel injection systems. The chemistry of the varying fuels as well as the concentration of fuel additive was found to strongly affect the tribofilm formation on the sliding surfaces. The fuel additive showed no friction or wear reducing effect in any of the fuels, except for in E85.
查看更多>>摘要：Sliding wear experiments were performed on the set of six Al-Al2O3 nanocermets, which were optimally designed with a tuned volumetric concentration of 20% Al and 80% Al2O3 to achieve a tailored cocooning of Al2O3 particles with thin Al film in the cermet structure. A combination of cryo-milling and room temperature ball milling was carried out to prepare Al-0.2-(Al2O3 )(0.8) powder mixtures and the nanocermets were prepared by spark plasma sintering (SPS). Pure Al, Al2O3 and nanocermet samples were subjected to a dry sliding wear test against a steel counter-body with the contact diameter of 1 mm to estimate their relative wear behaviour. The results suggest that the wear behaviour of nanocermets is comprised of both abrasive and adhesive losses. An increase in the milling duration of powder mixtures improved the wear resistance of the sintered nanocermets. Abrasion, adhesion, fracture, delamination and ploughing were found to be the major material removal mechanisms from the wear tracks. SEM was utilized to understand the morphological features of the wear tracks and wear debris, while XRD was used for the phase evaluation of the samples. HRTEM was used to observe the distribution of phases in the sintered nanocermet structure.
查看更多>>摘要：With the development of the nuclear industry, uranium materials with better wear resistance are demanded. This paper aims to demonstrate the effects of ultrasonic surface rolling process (USRP) on the tribological properties of uranium. Surface characteristics, i.e., surface topography, residual stress, microstructure, hardness and wear behavior, were examined. The results indicated that nanostructure, deformation twins and texture were generated on the uranium surface after USRP treatment. Surface roughness Ra, Rp and Rv showed a remarkable decline by 85.6%, 85.5% and 74.8% compared to the untreated specimen, respectively. Moreover, increased microhardness and enhanced residual compressive stress were obtained by USRP treatment. According to the wear tests against silicon carbide counterball in dry sliding conditions, the friction coefficient was decreased to 0.66 and the wear volume was also drastically reduced, which prolonged the friction and wear life of uranium materials. Additionally, it was concluded that abrasion wear, adhesion wear and oxidation wear played the dominant roles in the USRP treated specimens and the silicon carbide counterball showed the characteristics of abrasion wear.
查看更多>>摘要：The increased control of hydropower plants (i.e. shift from water level to primary control) leads to an increased number of load cycles on critical components such as bearings in hydropower turbines. Despite having shorter sliding amplitudes, this may result in a longer accumulated sliding distance that reduce the useful life of the bearings. In this study, the effect of stroke length on the tribological performance of two self-lubricating polymer composites, commonly used for bearings in hydropower turbines, during dry sliding against stainless steel is investigated. The reciprocating tests are carried out under relevant conditions, i.e. high pressures and long sliding distance, corresponding to years of operation of a hydropower turbine. The worn polymer and stainless-steel surfaces are examined using 3D optical surface profilometer and SEM/EDS to study the wear and friction mechanisms. The results show an increasing wear rate with increased stroke length for both bearing materials, especially when the stroke length is longer than the length of the polymer pin. The thermoset show the same trend for the frictional behaviour and it is attributed to decrease in coverage by transfer layers and solid lubricants at the sliding interface as well as increase in abrasive wear of the stainless steel. Meanwhile, the highest friction is observed at the shortest stroke length for the thermoplastic and the lowest at the intermediate stroke. Surface analysis reveals higher abrasive wear of the stainless-steel counter surface at the longest stroke length for both bearing materials due to lower wear particle entrapment. It can be concluded that changes in sliding amplitude have a significant influence on the tribological performance of the two polymer composites sliding against stainless steel.
NSTL
Elsevier