查看更多>>摘要：This article deals with the analysis of the subsurface deformation effects of materials due to the periodic action of liquid droplets, each with a constant volume of approximately 36 mm(3) distributed with a spatial frequency of 20,000 i/mm. Sample grooves were analyzed within standoff distances where the prevailing mechanism is acceleration culmination depletion using the stair trajectory to avoid a possible Doppler effect. Using X-ray mu-CT, a network of cavities corresponding to a fractal shape was identified below the surface. It is apparent that the ability to erode does not end with the formation of a groove but continues into the core of the material in the form of microjetting, tunneling, or piercing. From that perspective, two types of these cavities have been identified, blind and transient, with diameters of a few micrometers. The topological changes in the subsurface region of the sample were analyzed using X-ray tt-CT progressive sectioning. The anticipated subsurface deformation was further explored and analyzed using SEM analysis. The integrity of the material around the cavities was assessed according to microhardness to explain the microjetting, tunneling, and piercing propagation. The results suggest that the effect of the lateral jetting after droplet collapsing causes extensive hydrodynamic tunneling in the material that is much higher during the intense periodic action of water droplets, even at subsonic speeds.
查看更多>>摘要：The study aimed to investigate the dry sliding properties of as received copper based composite materials, with varying silica and copper content, and produced through two different techniques: conventional compaction and sintering and spark plasma sintering (SPS). The SPS process induced pronounced densification and hardness of the materials and a better distribution of constituents when compared to conventionally sintered specimens. The SPS specimens observed the presence of a C layer of varying thickness on their surfaces, transferred from the graphite die used for their production. The thickness and adhesion of the C layer was influenced by the silica content in the specimens. Specimens containing low silica content showed a significant C layer on the pin surface. This C layer was not removed during dry sliding pin on disc testing, thus resulting in very low COF (coefficient of friction) and pin wear. Specimens containing high silica content led to the formation of a sparse C layer on their surfaces due to the low chemical interactions of silica with other atoms or compounds, leading to easy removal during tests and elevated COF magnitude. However, high silica content also led to low adhesion between the friction layer and the worn surfaces, resulting in instability and higher pin wear. The specimens containing moderate silica content were identified as the best composition due to their ability to easily shed the C layer during testing, maintain smooth, compact, and continuous friction layer without any detachment/adherence issues, and demonstrate permissible COF and pin wear in the mild range.
Blades, LukeHills, DavidNowell, DavidEvans, Ken E....
9页
查看更多>>摘要：Whilst contact loading is known to affect wear, the general stress field is rarely considered. Steel fretting (and low amplitude reciprocating) wear contacts typically develop through a transient regime and wear by multiple mechanisms. It is expected that if these mechanisms were controlled by plasticity or fatigue, the wear rate would be altered by external stresses. Whether or not these stresses must be accounted for is an important consideration. This paper assesses the sensitivity of wear rate to external stresses, experimentally. An apparatus was designed to apply external loads to fretting wear contacts. The wear rates throughout the tests were insensitive to changes in external load, indicating that wear models need only model stresses due to contact loading, and external loads can be disregarded.
Torres, H.Podgornik, B.Jovicevic-Klug, M.Ripoll, M. Rodriguez...
10页
查看更多>>摘要：In recent years, the hot forming of aluminium has raised significant interest in industrial sectors such as the automobile and aerospace. However, such processes are not without difficulties, as the high adhesive wear characteristic of aluminium alloys is exacerbated at high temperatures and detrimentally affects the quality of the finished product. In an effort to improve this situation, different solid lubricant additives including hBN, graphite and graphene have been mixed with a commercial-grade lithium grease and evaluated under conditions representative of the high temperature forming of aluminium alloys, using an innovative single-pass, high temperature tribometer. Two different alloys have been chosen for the present study, including a nickel-based, self-lubricating laser cladding previously studied by the authors in the context of high temperature applications in addition to a reference tool steel widely used in metal forming industry. Experimental results showed a detrimental role of hBN as a solid lubricant, providing insufficient protection against adhesive wear and even leading to noticeable increases in the observed friction compared to other solid lubricants such as graphite. It has also been found that graphene excels at decreasing friction and material transfer from the aluminium counter body, suggesting a great potential as a lubricant additive in high temperature forming processes. However, the results of the present study indicate that graphene concentrations of 1 wt% are not enough for effective lubrication at high temperatures.
查看更多>>摘要：A consensus on the tribological performance of components by additive-versus conventional manufacturing has not been achieved; mainly because the tribological test set-ups thus far were not suited for investigating the underlying microstructure's influence on the tribological properties. As a result, utilization of additive manufacturing techniques, such as selective laser melting (SLM), for tribological applications remains questionable. Here, we investigate the anisotropic tribological response of SLM 316L stainless steel via in situ SEM reciprocating micro-scratch testing to highlight the microstructure's role. As-built 316L SLM specimens were compared against annealed wire-drawn 316L. We found that: (i) microgeometric conformity was the main driver for achieving steady-state friction, (ii) the anisotropic friction of the additively manufactured components is limited to the break-in and is caused by the lack of conformity, (iii) the cohesive bonds, whose strength is proportional to frictional forces, are stronger in the additively manufactured specimens likely due to the dislocation-dense, cellular structures, (iv) low Taylor-factor grains with large dimension stimulate microcutting in the form of long, thin sheets with serrated edges. These findings uncover some microstructurally driven tribological complexities when comparing additive to conventional manufacturing.
查看更多>>摘要：Wear in rolling contact is a complex phenomenon because it is multi-scale and multi-physical by nature and involves many strongly correlated parameters. It makes the numerical calculation of wear very challenging. In order to simulate wear, a better understanding of the influencing parameters involved in the wear calculation is of importance. This work presents a new numerical calculation of railway wheel wear based on Archard's equation combined with a spatial statistic approach called the Universal Kriging technique. The influence of factors, such as the contact mechanics model and the wear coefficient were studied through numerical experiments. The outcomes provide a new insight into the roles of the contact modelling and of the uncertainties of the wear coefficient in the numerical calculation of wear under various contact conditions. By considering the uncertainties of the wear coefficient, the approach provides a min.-max. range for wear estimation instead of a single deterministic value; furthermore, it can provide a detailed wear distribution over the contact patch for damage analysis. In combination with an accurate model of wheel-rail contact, this new wear model offers a more realistic wear prediction compared to the methods presently used for wheel wear estimation in railway vehicles.
查看更多>>摘要：To alleviate the fretting damage of the locking pin in variable-gauge train, the substrate (AISI 4135 steel) was surface-treated with laser quenching (LQ), plasma nitriding (PN), and bonded MoS2 coating respectively. Their fretting behavior and wear mechanism under grease lubrication conditions were experimentally analyzed. The results indicated that the two surface strengthening measures (LQ and PN) significantly improved the wear resistance of the substrate. The lowest energy dissipation occurs on the bonded MoS2 coating, but its low surface hardness results in the largest abrasion loss. Furthermore, a high-hardness and rough Fe-N compound layer was generated on the PN-treated surface, which is conducive to the formation of synergistic lubrication at the contact interface with grease, and had the optimum effect of reducing fretting damage. This study provides solutions and application reference for the surface engineering protection of similar mechanical components in the engineering field.
查看更多>>摘要：An effort is made to circumvent the negative effects on the outstanding processability and mechanical properties of poly-ether-ether-ketone (PEEK) when it is blended with solid lubricant (e.g., polytetrafluoroethylene (PTFE)) to improve its tribological performance. A hybrid wear method by composing different type of polymers is proposed and the role of various fillers (i.e., nano-sized, micron-sized particles and short cut carbon fibers) in the PEEK-PTFE-steel hybrid wear system is investigated. Imitating the working condition of a sliding bearing, experiments are conducted under dry conditions on a newly-developed dual-pins-on-disk tribometer in which unfilled PEEK and PTFE composite pins filled with various fillers slide against steel rings in the same wear track. The results reveal a synergistic effect between the two polymer components happened and then improved the tribological performance of the hybrid system. The PTFE composite wear debris generates a fluorine-based tribofilm on the sliding surfaces (i.e., the transfer film on the steel surface, the running film on the PTFE surface, and the secondary transfer film on the PEEK surface), transforming the wear process into one of sliding between the slippery tribofilms. In turn, the hard PEEK component crushes the PTFE wear debris to improve the quality of the formed tribofilms and compacts the transfer film to be thin and uniform.
查看更多>>摘要：This paper investigates the effect of interface modification on the microstructure and on impact abrasive wear behavior of zirconia toughened alumina particle (ZTAp) -reinforced iron-matrix composites. In order to improve the interface bonding between ZTAp and iron matrix, ZTAp was wrapped with Ti-Ni-Cu mixed powder (Ti-Ni-Cu@ZTAp), and then the Ti-Ni-Cu@ZTAp/Fe45 composite (modified composite) was prepared by vacuum sintering. The results show that a metallurgical bonding interface layer of 15-25 mu m thickness between the modified ZTAp and the iron matrix is formed, which improves their interface bonding. The modified composite presents better wear resistance compared with the unmodified composite and the relative wear resistance of the modified composite reaches the maximum value of 1.88 at 2J. In addition to good bonding, the interface layer with medium hardness and modulus reduces difference between the modified ZTAp and the iron matrix in terms of mechanical properties and behaviors under impact of abrasives, which can play a force transition role and release stress through its plastic deformation. Therefore, the modified ZTAp is more difficult to fall off from the matrix and has a longer protective effect on the matrix.
查看更多>>摘要：This paper investigates how nano-SiO2 interacts with NBR to affect the tribological properties of water-lubricated NBR-based composites using the Rtec friction and wear tester and the molecular dynamics simulation method. The surface-modified nano-SiO2 (SiO2(TESPT)) particles were prepared by modifying the hydroxyl groups on the surface of nano-SiO2 with Silicon 69 (TESPT), and cast copper alloy (ZCuSn10Zn2) was used as the counterface material in the friction test and wear test. The results showed that different interfacial interplay between nano-SiO2 and NBR makes for distinct wear mechanisms of NBR-based composites. With weak interface bonding between nano-SiO2 and NBR, NBR/SiO2 can easily get worn as nano-SiO2 particles detach from the matrix during the wear process, leaving pits and cracks on the worn surface. Instead, SiO2(TESPT) has stronger interface bonding with the matrix, which can prevent the detachment of SiO2(TESPT) restrict the movement of molecular chains in NBR, and reduce the temperature peak of the friction pair. SiO2(TESPT) exerts a dual influence on the tribological properties of NBR: while significantly improving the wear resistance of NBR, it can also notably increase the friction coefficient of the composite.
NSTL
Elsevier