Leticia Maria AnselmoThiago de Souza LamimMatheus HromatkaJose Daniel Biasoli de Mello...
15页
查看更多>>摘要：This paper aims to investigate the effect of post-sintering sizing process on the tribological performance of self-lubricating iron-based composites. Hollow cylindrical specimens were produced by powder metallurgy. Sizing was performed by repressing the as-sintered specimens in a hydraulic press die at three different pressures: 160, 320, and 480 MPa. The tribological characterization was carried out by reciprocating dry sliding tests using a ball-on-cylinder configuration. Variable load tests were performed to evaluate the scuffing resistance, whereas constant load tests were used to assess the wear rate and friction coefficient of the composites. The results show a gradual sealing effect of porosity and lubricants reservoirs and the hardening of the surface metallic matrix (up to 98%). The scuffing resistance was reduced by 72% at higher sizing pressures due to the lower availability of solid lubricants on the surface to maintain the tribolayer. The improved surface finishing and metallic matrix hardness reduced up to 70% of the tribosystem's wear rate at 320 MPa of sizing pressure. Furthermore, a detrimental effect on the wear resistance was noticed for the specimen sized at a higher sizing pressure (480 MPa), showing the importance of optimizing the sizing pressure to improve the tribological behaviour of sintered self-lubricating composites.
查看更多>>摘要：To investigate the influence of (Ti, Mo) C particles on the abrasive wear-corrosion resistance of low alloy martensitic steel, a comparative study on the abrasive wear, corrosion and abrasive-wear corrosion behaviors of JFE400, Ti20, and Ti60 (with carbide contents of 0%, 0.67%, and 3.25%, respectively) was conducted. The results indicated that owing to the hindrance of carbides on abrasive microploughing, the abrasive wear resistance of these materials was strengthened by increasing carbide content. However, galvanic corrosion can occur between (Ti, Mo) C particles and the Fe matrix, thereby weakening the obstructive effect under the abrasive wear-corrosion condition. Therefore, abrasive wear-corrosion resistance decreased in the following order: Ti20, JFE400, and Ti60. That means that Ti60, which contained the highest amount of carbide, showed the best abrasive wear resistance, but the poorest abrasive-corrosive resistance.
查看更多>>摘要：A model developed to represent the progress of erosion damage in liquid-metal spallation target vessels was modified to incorporate the effect of gas injection on the erosion rate. The liquid mercury target system for the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory now operates with helium gas injection to reduce target vessel fatigue stress and cavitation-induced erosion damage. Erosion damage is a primary degradation phenomenon affecting the service life of SNS target vessels, and cavitation mitigation techniques, such as small-bubble gas injection, have been implemented to reduce damage and extend target lifetimes. Erosion depths in samples removed from SNS targets after operation were measured using laser line scanning. These measurements confirmed that gas injection reduced erosion damage. However, quantifying the damage reduction due to gas injection was complicated by variations in lifetime, power, and gas injection rates between different targets. In this study, the operating power and gas injection rate of targets were incorporated into an erosion damage prediction model to quantify their effects on erosion damage reduction. Values of a power scaling factor, β, were calculated by comparing modeled with measured erosion damage. These values indicate that the use of gas injection at the SNS reduced damage to a level equivalent to operating targets without gas injection at 35-47% of the actual beam power. To account for the gas injection effect on the cavitation damage, a simple exponential form based on analysis of the scaling factor β was developed to incorporate the gas rate history with a scaling factor γ in the erosion damage modeling.
查看更多>>摘要：Systematic experimental investigations were conducted to study the damage behavior of rail steels with eutectoid and hypereutectoid microstructure under different axle load and curve radius conditions. The wear resistance and resulting failure mechanism, as well as subsurface crack development were evaluated by wheel/rail rolling contact test rig, which can realize a broad range of working conditions from mild condition to harsh condition. Results demonstrate that the wear resistance and rolling contact fatigue (RCF) damage depend on not only the working conditions employed, but also the microstructures. With the increase of axle load and reduction of curve radius, the wear rate increases for both rail steels. Damage mechanisms for the two rail materials are mainly surface fatigue cracks and delamination, which become much serious from the mild condition to harsh condition. The hypereutectoid rail possesses a better wear resistance than eutectoid rail in general. Wear regime map suggests that the hypereutectoid rail did not have a catastrophic wear region, but can be observed in eutectoid rail. The subsurface analysis shows that the working condition has a significant impact on surface crack development depending on specific microstructure types. The hypereutectoid rail is more suitable for harsh working conditions than eutectoid rail.
查看更多>>摘要：Wire saw cutting of monocrystalline silicon plays an important role in semiconductor manufacturing. The study of wire saw cutting silicon is important, and the grain wear has a great effect on the saw cutting force. Therefore, in this paper, considering abrasive wear on the wire saw, the ultrasonic vibration assisted sawing force theoretical model from a single abrasive to multiple abrasives is established. With the application of equal probability method, the surface profile model of wire saw is established. According to the abrasive wear law of wire saw, the finite element model (FEM) of wire saw with different abrasive wear is established. The influence of different abrasive wear on sawing force and workpiece surface morphology is analyzed by Abaqus. Finally, the experimental verification is carried out. The experimental results show that the sawing force of the ultrasonic vibration assisted diamond wire sawing (UAWS) decreases by 38% on average than that of the conventional diamond wire sawing (CWS), the surface roughness value is reduced, and the surface morphology is improved. With the increase of the abrasive wear value, the sawing force and the numbers of pits firstly decrease and then increase, the surface roughness value distribution firstly concentrates and then disperses, and the scratches show a smooth to intermittent trend.
V. JavaheriS. SadeghpourP. KarjalainenM. Lindroos...
13页
查看更多>>摘要：The extremely altered topmost surface layer, known as the white layer, formed in a medium-carbon low-alloy steel as result of impacts by angular 10-12 mm granite particles during the slurry erosion process is comprehensively investigated. For this purpose, the characteristics, morphology, and formation mechanism of this white layer are described based on the microstructural observations using optical, scanning and transmission electron microscopies as well as nanoindentation hardness measurements and modelling of surface deformation. The white layer exhibits a nanocrystalline structure consisting of ultrafine grains with an average size of 200 nm. It has a nanohardness level of around 10.1 GPa, considerably higher than that of untempered martensitic bulk material (5.7 GPa) achieved by an induction hardening treatment. The results showed that during the high-speed slurry erosion process, solid particle impacts brought forth conditions of high strain, high strain rate, and multidirectional strain paths. This promoted formation of a cell-type structure at first and later, after increasing the number of impacts, development of subgrains following by subgrain rotation and eventually formation of a nanocrystalline structure with ultra-high hardness. The model confirmed that high strain conditions - much higher than required for the onset of plastic deformation - can be achieved on the surface resulting in severe microstructural and property changes during the slurry erosion test.
查看更多>>摘要：With the aim to apply thermoplastics as sliding bearing pads against stainless steel runner under heavy loads suffering temporary lack of lubricants, the tribological performance of polyetheretherketone (PEEK) was examined using a pin-on-disk tribometer with a thermocouple embedded in a stainless-steel pin under a dry friction condition. With an increase in specific pressure (from 0.7 to 2.8 MPa) and sliding velocity (from 0.26 to 0.65 m/s), the friction coefficient of the pure matrix increased from 0.06 to 0.60 with measured interface nominal temperature rising from 42℃ to 161℃, while the PEEK reinforced with carbon fiber (CF)/graphite/polytetrafluoroethylene (PTFE) exhibited a lower friction coefficient between 0.06 and 0.35 and a lower temperature ranging from 29℃ to 53℃. The interface temperatures play a key role dominating the wear behaviors of PEEK blends. The specific wear rates of PEEK blends increase exponentially when the ambient temperature exceeds 150℃. It is essential for PEEK blends to keep the interface temperature below the glass transition temperature to achieve remarkable tribological behavior. It is suggested that the CFs provide high thermal conductivity and resistance at the contact deformation in addition to the solid lubrication provided by the graphite/PTFE at the interface.
查看更多>>摘要：In situ synthesis of graphene reinforcements in Ni matrix is a promising strategy to manufacture graphene/Ni composites for advanced lubrication. However, the influence of in situ grown graphene content on the tribological properties and the lubricating mechanisms of the graphene/Ni composites under ambient air are far from clear. According to the dissolution and precipitation of carbon on Ni grain surface, this paper reports a high-quality graphene/Ni self-lubricating composite synthesized by in situ powder metallurgy process. The micro-structure and tribological behaviours of the composites with different graphene content are elaborated. It is found that the in situ grown few-layer graphene can induce a significant grain refinement effect and simultaneously achieve excellent anti-friction and wear performances. The lowest friction coefficient and wear rate of 0.254 and 4.385 × 10~(-5) mm~3/(N·m) are obtained by the graphene/Ni composite with 0.6 wt% carbon. In comparison with pure Ni, the friction coefficient and wear rate are reduced by 3.02-fold and 3.44-fold, respectively. The tribological improvements of the presented graphene/Ni composite is related to the high H/E ratio and homogenous dispersion of graphene nanosheets.
查看更多>>摘要：A pin-on-disk tribotester has been designed and constructed that enables cryogenic friction and wear testing to be conducted either in liquid nitrogen (wet tests) or in dry sliding conditions. The tester does not require a sealed, cooled cryostat for the cryogenic tests. For wet tests, both pin and disk specimens are immersed in liquid nitrogen (LN2), whereas for the dry cryogenic tests, the disk specimen is only partially submerged in LN2 while the pin specimen remains dry in gaseous nitrogen. To prove the capabilities of the tribotester, tests were run using AISI 316 stainless steel pins in sliding contact with disks made of yttria-stabilized zirconia. Friction and wear tests were run under three conditions: dry sliding in room temperature air, cryogenic dry sliding in which bulk pin temperatures remained less than 115 K, and wet cryogenic tests in LN_2 at 77 K. All tests were run at two different sliding speeds, 0.1 and 1.0 m/s, for a sliding distance of 1 km. It was found that wear rates of the stainless steel material were slightly lower at cryogenic temperatures than at room temperature, with wear being greater at low sliding speed than at high speed for all test conditions. Friction coefficients in the cryogenic tests were generally slightly lower than those at room temperature. X-ray diffraction analysis of the worn AISI 316 stainless steel pin surfaces showed that phase transformation from austenite to martensite had occurred during all cryogenic wear tests, whether in liquid nitrogen or during dry sliding, as well as during tests in air at room temperature. More martensite was produced during low speed sliding tests, both wet and dry, when the wear rates were higher, than at high sliding speeds. X-ray photoelectron spectroscopy analysis of worn pin surfaces was conducted to determine the role of oxides in the wear process at both room and cryogenic temperatures.
NSTL
Elsevier