Do two different and independent methods of estimating the wear rate of a test sample yield the same numerical result? Numerical values of specific wear rates estimated on the basis of alternative ...methods using a set of dry sliding rotary-pin-on-disk experiments are presented. Wear rates of brass and aluminium alloy pins were estimated using gravimetric and wear scar area methods. Gravimetric and linear displacement methods were used to assess wear rates of ABS plastic and machinable wax pins. Scepticism about the estimated nominal values of wear rates is reduced when alternative assessment methods result in comparable numerical values, or values having the same order of magnitude. This is particularly useful when ranking competing materials for wear rates, when the differences in these rates are small. Uncertainties in individual test sample wear rates, and dispersion in the nominal values of wear rates are also computed to support the aforementioned observations.
•The results of the scraping tests demonstrate a clear correlation between hardness, applied load, and grain size.•In all analyzed cases, the maximum loading force of monocrystalline materials ...exceeds that of polycrystalline substances.•As the aluminum composition and temperature increase, both the loading force and hardness exhibit a decrease.•As the scraping depth increases, there is a simultaneous augmentation in loading force, stress, strain, and deformation. This occurrence is attributable to the enlargement of the contact area between the tool and specimen as the scratching depth advances.
This investigation utilizes molecular dynamics simulations to explore the mechanical response of the AlCuCrFeNi high-entropy alloy to nano-scraping employing an abrasive tip traversing the workpiece surface. This study investigates the influence of various parameters, such as grain size, pressing depth, alloy composition, temperature, and sliding distance, on plastic deformation, frictional behavior, dislocation density, wear mechanisms, and von Mises stress. The results reveal that increasing grain size leads to augmented force and hardness, indicative of a reverse Hall-Petch relationship. Moreover, scraping and indentation forces escalate with decreasing aluminum concentration and temperature. The analysis underscores the pivotal role of grain boundaries in impeding stress and strain propagation. Stress and strain concentrations are particularly evident at the interface between the scraping tool and the substrate and near the grain boundaries. Grain boundary slipping, bending, and grain merging are pivotal mechanisms contributing to the distortion of polycrystalline materials, culminating in solid dislocations within grain boundaries. Furthermore, heightened compression depth and sliding distance exacerbate plastic deformation and subsurface damage. Notably, the presence of copper atoms enhances the HEA's resistance to deformation. This research enhances comprehension of the nano-scraping behavior and deformation mechanisms in AlCuCrFeNi HEA during ultra-precision processing.
Graphic abstract of Machining mechanism and residual stress of AlCuCrFeNi alloy: (a) the simulation model grain coloring atomistic model, (b) the loading-time curves, (c) atomic distribution, (d) the deformation area, (e) the von Mises stress dispersions, (f) the dislocation length under the indentation and scraping process. Display omitted
TiN/TiO2 composite ceramics coatings have been deposited on the surface of Q345B structural steel using supersonic dual-filament arc spraying. The structural, mechanical, wear resistance and ...corrosion resistance properties of TiN/TiO2 composite ceramics coatings were systematically analyzed using various characterization techniques. The physical and chemical compositions, surface morphology, Young's modulus and hardness of the coatings were analyzed using XRD, XPS, SEM, EDS and nanoindentation. The corrosion resistance properties of the coatings were evaluated using potentiodynamic polarization tests in a 3.5 wt% NaCl solution. The wear condition and specific wear rate of linear reciprocating friction of the coatings and Q345B against GCr15 steel balls at different normal loads of 5 N and 10 N and in a 3.5 wt% NaCl corrosive solution environment were investigated using a Rtec-multifunctional friction machine. The wear surface and wear mechanism were also analyzed. The results show that the coating thickness is approximately 300 μm, the internal structure is uniform and dense, and the overall porosity is low, exhibiting a certain laminar structure. The coating exhibits extremely high hardness and high Young's modulus of 26.3 GPa and 264.3 GPa, respectively, with a 10.2-fold increase in hardness over the substrate. The corrosion current of the coatings decreased by three orders of magnitude compared to the substrate, with higher polarization resistance and charge transfer resistance. In wear tests under different conditions, the coatings exhibit perfect wear resistance characteristics, with a specific wear rate of only 5.19%–14.48% of the substrate specific wear rate.
This research paper investigated the hardness and tribological performance of novel Grewia optiva/Basalt fiber reinforced hybrid polymer composites. Two different configuration of hybrid composite ...that is, woven and chopped fiber reinforced composite are considered for the study. The chopped fiber configuration of the composite is further divided into two types based on fiber length and wt%. The fiber lengths studied are 6 and 12 mm while the wt% studied are 0, 6, and 12 wt%. Woven fiber reinforced composite is divided into five configurations based on wt% of G. optiva fiber with 0, 3, 6, 9, and 12 wt%. In all configurations, maximum fiber content of 12 wt% is maintained. B6/GO6 composite exhibits minimum specific wear rate and maximum hardness among all the compositions. Wear experimental results are analyzed by Taguchi optimization technique and based on the five levels and four control factors (sliding velocity, fiber loading, sliding distance, and normal load) L25 partial orthogonal array was suggested for the woven fiber reinforced composites. Fiber content is the main control parameter for hardness testing and L9 orthogonal array was suggested according to four control factors and three levels.
Abstract
Wear-related energy and material loss cost over 2500 Billion Euro per year. Traditional wisdom suggests that high-strength materials reveal low wear rates, yet, their plastic deformation ...mechanisms also influence their wear performance. High strength and homogeneous deformation behavior, which allow accommodating plastic strain without cracking or localized brittle fracture, are crucial for developing wear-resistant metals. Here, we present an approach to achieve superior wear resistance via in-situ formation of a strong and deformable oxide nanocomposite surface during wear, by reaction of the metal surface with its oxidative environment, a principle that we refer to as ‘reactive wear protection’. We design a TiNbZr-Ag alloy that forms an amorphous-crystalline oxidic nanocomposite surface layer upon dry sliding. The strong (2.4 GPa yield strength) and deformable (homogeneous deformation to 20% strain) nanocomposite surface reduces the wear rate of the TiNbZr-Ag alloy by an order of magnitude. The reactive wear protection strategy offers a pathway for designing ultra-wear resistant alloys, where otherwise brittle oxides are turned to be strong and deformable for improving wear resistance.
Cryogenic treatment, also known as subzero heat treatment, is a cooling process that complements conventional heat treatment to improve the properties of metals. Unlike coatings, it is a one-time, ...inexpensive, permanent operation that affects the entire part. This method is mainly applied to tool steels used in mold making. In this study, the changes caused by the effects of shallow and deep cryogenic treatment on Sleipner cold work tool steel were investigated in terms of microhardness, microstructure, coefficient of friction (COF), and wear rate (WR). For this purpose, the test specimens were subjected to the cryogenic treatments performed at two different temperatures (−80 ºC for the shallow cryogenic treatment (SCT) and − 180 ºC for the deep cryogenic treatment (DCT)) and various retention times (12 h, 24 h for SCT and 12 h, 24 h, 36 h for DCT). Dry sliding wear tests were carried out under different loads (10 N and 20 N) and varying test durations (60, 120, and 240 min) at a constant sliding speed of 0.075 m/s. According to the microhardness results, it was determined that the cryogenic treatment increased the hardness by 6.53 %. According to the microstructure investigations, a more homogeneous structure was observed with the cryogenic treatment, and secondary carbide precipitations were detected. It was observed that the conventional heat-treated (CHT) sample gave the highest COF value with an average coefficient of friction of 0.63. The lowest COF value of 0.58 was observed in the DCT-12 sample. After the wear tests, the lowest wear rate value for both load values was obtained from the DCT-36 specimen.
•Sliding of grain boundary and grain growth play a key role in the plastic deformation mechanism.•Atoms in a state of high stress-strain are located around the abrasive tip and in the grain ...boundary.•The reverse Hall-Petch relationship is observed within the grain size range of this study.•The ability to lose the material volume of a polycrystalline is larger than a single-crystalline.
The mechanical response of CuAlNi nanocrystalline under the nanoscratch through an abrasive tip sliding on the workpiece is investigated using molecular dynamics (MD) simulation. The influences of the grain size, alloy composition, temperature and scratch speed on the plastic deformation characteristic and wear mechanism are surveyed. The results represent that increasing the grain size leads to higher force and hardness, which suggests the reverse Hall-Petch relationship. Meanwhile, the indentation and scratch forces tend to increase when reducing the Cu content and temperature, increasing the scratch speed. The deformation behavior exhibits that grain boundaries play a key role in inhibiting the spread of strain and stress. The results show that the stress and strain are concentrated not only in the contact region between the abrasive tip and substrate but also in the grain boundary and adjacent grain boundary areas. Notably, the sliding, twisting of grain boundary and the fusion of grains are a significant mechanism in the deformation behavior of polycrystalline, resulting in the dislocation is strongly developed in the grain boundary. Furthermore, the movement of atoms in various directions leads to different morphology of pile-up. From quantitative results of the special wear rate show that the ability to lose material volume is larger with Cu86Al11Ni3 alloy and at a temperature of 600 K, as well as the polycrystalline is higher than the single-crystalline. Finally, the residual depth ratios exhibit more strain recovery at the grain size of 6.17 nm and lower temperature.
The figure shows the workpiece model (a) and the evolution of grain of CuAlNi alloy at different positions: (b1) before scratching, (b2) an indentation depth of 2.0 nm, (b3) a scratching distance of 1.0 nm, (b4) a scratching distance of 4.0 nm, (b5) a scratching distance of 8.0 nm. Display omitted
Tribological behavior of the model AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) sliding against different counterfaces including Al2O3, Si3N4, SiC ceramics and GCr15 steel at room temperature ...(RT), and particularly SiC at elevated temperatures were investigated. Our EHEA was found to maintain high hardness (＞197 HV) up to 900 °C. The RT tribology tests show that the friction and wear of the EHEA are slightest when against SiC. The wear rates of the EHEA increases monotonously from RT to 900 °C, but the friction coefficient drops sharply (＜0.35) when the temperature exceeds 600 °C. This is attributed to the enhancing in the oxidative wear and the formation of deformed fine-grained layer beneath the worn surface.
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•Tribological behavior of the AlCoCrFeNi2.1 EHEA against different counterfaces was investigated.•The EHEA/SiC tribo-pair shows the optimal compatibility at RT.•The high hardness of over 197 HV of the EHEA could be maintained up to 900 °C, superior to the Inconel 718 superalloy.•The EHEA exhibits good wear resistance over a wide temperature range from RT to 900 °C.
Silicon carbide ceramics have many excellent properties, such as high melting point, high strength, high thermal conductivity, high hardness, high stiffness, good chemical resistance, good electrical ...conductivity and remarkable wear resistance. Therefore, SiC ceramics are useful for various tribological applications. Nevertheless, SiC ceramics usually exhibit poor friction characteristics under unlubricated sliding contacts, which can greatly deteriorate the durability and reliability of a tribosystem. In this work, the tribological research progress of SiC ceramics was summarized based on microstructural characteristics, self-lubrication methods, surface characteristics and external factors. First, tribological performance of SiC ceramics can be improved by controlling microstructural characteristics, such as reducing grain size of SiC ceramics, acquiring elongated SiC grains, reducing the content of grain boundary/intergranular phase, crystallizing amorphous grain boundary phases, hardening intergranular phases, controlling cracks propagation way. Second, good self-lubrication property for SiC ceramics can be obtained by annealing heat treatment, adding the secondary phase or producing porous SiC ceramics. Third, tribological performance of SiC ceramics can be improved by proper surface processing or surface modification, such as proper roughness, surface texture or coating technology. Fourth, tribological performance of SiC ceramics is affected by various external factors. Besides, the research trends of SiC ceramic tribology in future were proposed. This work aims to provide some reference for the design of SiC ceramics with high wear resistance and low friction.
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•The effect of microstructure on tribological property of SiC ceramics is discussed.•The self-lubrication methods for SiC ceramics are elaborated.•The influence of surface features on tribology of SiC ceramics is evaluated.•The effect of external factors on tribological property of SiC ceramics is described.•The future research trends are proposed to provide some guidelines for tribologists.
The authors propose a new philosophy and theory for rubber friction and wear that are significantly different from the existing classical theories. Several distinctive features of rubber friction ...such as the exceedingly high friction coefficient and the intense stick-slip motion during frictional sliding all result from the sticky surface behavior exhibited by a cross-linked rubber, where there is a meniscus force brought about at the interface between the rubber and the rigid surface. The total friction coefficient μall incorporates three factors including an adhesion term μadh, a deformation term μdef and a crack formation term μcrac. This generates an equation μall =μadh +μdef +μcrac ≒ K1ηv1+ K2 (tanδ2)+ 2Kεc) E-7/6 W1/6 where η is the viscosity of the uncross-linked phase, E the modulus of the cross-linked rubber, v sliding velocity, c crack length, W normal load, K1, K2, Kεare all coefficients whose characteristics also govern rubber wear. The adhesion term is the most dominant factor during rubber friction, which roughly contributes about 70–80% of the total friction coefficient according to a very rough estimation.
The close relationships between the observed stick-slip motion, abrasion pattern formation and wear have been verified experimentally. The abrasion pattern is initiated by the high frequency vibration and the steady abrasion pattern together with steady wear is promoted by the stick-slip motion. Steady wear rate V˙ could be estimated theoretically as a function of the steady abrasion pattern distance Dab using an equation V˙ = k’Dab3, which indicates that many of the characteristics observed in rubber wear are also fundamentally governed by the intense stick-slip motion induced by the sticky rubber surface.
This figure shows schematically the meniscus formation by the uncross-linked phase and the Van der Waals contact by the cross-linked phase in the interface between the cross-linked rubber and solid, where the meniscus force generates the most significant adhesion friction coefficient for rubber friction together with high surface stickiness and violent stick-slip motion. Display omitted
•A new theory of rubber friction, one that differs significantly from the existing classical theories, is proposed.•The adhesive component dominates the friction coefficient of rubber, comprising almost 70–80% of its magnitude.•The close relationship between stick-slip motion, abrasion pattern formation, and wear were validated by both experiments and theory.
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