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Macroscale superlubricity on engineering steel surfaces offers a promising solution for minimizing friction and wear in engineering applications. However, achieving superlubricity typically requires a long running‐in period, which may result in significant wear for the friction pair. Herein, a new lubricant with superlubricating properties is rationally designed by using polyethylene glycol (PEG) and critic acid (CA) under complexing effect with a running‐in period of about 800 s. Importantly, the introduction of carbon quantum dots (CQDs) obtained from the pyrolysis of CA into PEG aqueous solution shortens the running‐in period for achieving macroscale superlubricity (µ ≈ 0.005) between steel/steel contact to 44 s. The corresponding wear rate (1.15 × 10−7 mm3 N−1 m−1) on the steel disk is reduced by 77% due to the shorter running‐in time. Furthermore, the surface analysis combined with the molecular dynamics simulations demonstrates that CQDs easily adsorb on the surface of the friction pair, forming a carbon film that reduces interaction energy between the lubricant molecules and the substrate. This work provides new insights into the lubrication mechanism of CQDs and contributes to the design of liquid superlubricants with short running‐in periods and low wear rates on engineering steel surfaces. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the effect of V doping on the microstructure, chemical stability, mechanical and vacuum tribological behavior of sputtered MoS2 coatings. Design/methodology/approach: The MoS2-V coatings are fabricated via tuning V target current by magnetron sputtering technique. The structural characteristic and elemental content of the coatings are measured by field emission scanning electron microscopy, X-ray diffractometer, electron probe X-ray micro-analyzer, Raman, X-ray photoelectron spectroscopy, high resolution transmission electron microscope and energy dispersive spectrometer. The hardness of the deposited coatings are tested by a nanoindentation technique. The vacuum tribological properties of MoS2-V coatings are studied by a ball-on-disc tribometer. Findings: Introducing V into the MoS2 coatings results in a more compact microstructure. The hardness of the coatings increases with the doping of V. The MoS2-V coating deposited at a current of 0.2 A obtains the lowest friction coefficient (0.043) under vacuum. As the amount of V doping increases, the wear rate of the coating decreases first and then increases, among which the coating deposited at a current of 0.5 A has the lowest wear rate of 2.2 × 10–6 mm3/N·m. Originality/value: This work elucidates the role of V doping on the lubrication mechanism of MoS2 coatings in a vacuum environment, and the MoS2-V coating is expected to be applied as a solid lubricant in space environment. [ABSTRACT FROM AUTHOR]

The multi-sensor scheduling problem of dual unmanned flight platforms has a complex coupling relationship, and how to reasonably match flight segments, sensors and targets is an intricate part of the problem. To solve the multi-sensor scheduling problem of dual unmanned flight platforms, a flight segment task allocation mechanism was proposed in this study, which assigned tasks through the position relationship between the flight segment and the target. This mechanism could effectively split the tasks and solve the task coupling problem of the two platforms. Pre-processing targets and sensors were carried out to identify scarce sensor resources and independent targets in advance to guide subsequent scheduling matching. Then, sensor-target matching was carried out to plan the scheduling of sensors based on the task revenue. The scheduling of conflicting segments was adjusted according to the availability of sensor resources. Finally, task migration was carried out for targets that still need to complete their assigned tasks. The available free sensors in the corresponding flight segments were matched according to the target task remaining to improve the task revenue. In order to verify the effectiveness of the proposed algorithm in this study, existing algorithms were compared through simulation experiments on 10 test problems. The experimental results showed that this algorithm outperformed existing algorithms in task revenue and stability with a significant reduction in running time. [ABSTRACT FROM AUTHOR]

The turnover rate of social workers is extremely high and the predictive roles of professional identity and job burnout on turnover intention have not been explored in China. The study examined the relationship between professional identity and turnover intention, mediated by job burnout and moderated by a social work degree, amongst social workers in China. Based on a sample of 829 participants and the structural equation model method, the findings confirmed that professional identity per se was not related to turnover intention, and a mediating role of job burnout and a moderating role of a social work degree were identified. [ABSTRACT FROM AUTHOR]

Low pay and the absence of professional identity (PI) are often blamed as major antecedents related to the turnover of social workers in China, yet no study has provided any consideration of the two antecedents together in predicting the turnover intention (TI) of social workers and comparing them, which acts as a more powerful predictor. Based on a sample of 819 participants and by using structural equation models, the current study indicated whether pay satisfaction (PS) or PI could predict TI; the results show that PS plays a stronger role. The findings identified the mediating role of PI in the relationship between PS and TI, but the moderating role of the type of sector (TS) was not supported. The findings suggest that it is necessary to advocate for adequate pay for social workers all over the world. Additionally, PI should be a top priority in social work education, training, exams and practice. Meanwhile, the government should strengthen the purchase of social work services, and a greater proportion of purchase money should be used to pay social workers. Furthermore, the government could offer subsidies for social workers employed in the private sector, similar to those employed in the public sector. [ABSTRACT FROM AUTHOR]

Thick diamond‐like carbon (DLC) coatings with different silicon (Si) transition layer thickness are deposited by hollow cathode plasma immersion coating technology. The results show that the internal stress of the coating can be tuned by changing the deposition time of Si transition layer, thereby obtaining good adhesion strength. Friction and wear results show that all coatings have good tribological properties. The coating with 8 min Si transition layer (Si‐8) demonstrates the lowest friction coefficient (μ ≈ 0.03), even achieves ultralow friction (μ ≈ 0.008) for a short time. However, the wear rate of Si‐8 coating is found to be the largest (2.1 × 10−16 m3 (N m)−1. The low friction coefficient of Si‐8 coating is related to its high degree of graphitization, complete transfer film and fine wear debris. In contrast, the Si‐16 coating has the lowest wear rate of about 5.6 × 10−17 m3 (N m)−1 with a relatively high friction coefficient (μ ≈ 0.1). This is due to its high hardness and the formation of a nano‐twisted double helix carbon debris during the friction process. This nano‐twisted double helix structure can consume additional plastic deformation energy, while reducing the interface contact area and increasing the interface bearing capacity, thereby improving the wear resistance of the thick DLC coating. [ABSTRACT FROM AUTHOR]

Abstract Coating oxidation performance is a major concern in modern machining and other high temperature applications. This study presents TiAlCrN composite coatings with different Cr content prepared on a magnetron sputtering device. SEM, AFM and XRD were used to determine the structure of the coatings. It was found that the coatings show a solid solution of B1-NaCl face-centered cubic structure with [200] preferential orientation. As the Cr content increases, the particle size and roughness of the coating increase slightly, while the hardness of the coating decreases. Oxidation tests revealed that no significant oxidation occurs in all coatings below 800 °C. However, as the oxidation temperature increases to 1000 °C, the Ti 0.32 Al 0.38 Cr 0.30 N coating undergoes severe oxidation and the Ti 0.17 Al 0.19 Cr 0.64 N coating remains good. The oxide scale of the coatings after oxidation test is analysis by XPS depth profiling in details. XPS results revealed that the oxide scale of the Ti 0.32 Al 0.38 Cr 0.30 N coating changes from a dense Al rich oxide layer (800 °C) to a loose and discontinuous Ti Al rich oxide layer (1000 °C), which is the main reason for its poor oxidation resistance. However, the Ti 0.17 Al 0.19 Cr 0.64 N coating shows a top loose Ti Al rich oxide layer and a dense bottom Cr Al rich oxide layer. The presence of this dense and continuous Cr Al rich oxide layer can limit the rapid diffusion of Ti atoms to the surface while preventing the oxygen atoms from diffusing into the interior, which is the key to excellent oxidation resistance of the Ti 0.17 Al 0.19 Cr 0.64 N coatings. Highlights • The oxide scale of TiAlCrN coating was characterized by XPS depth profiling. • As the chromium content increases, the oxidation resistance of the TiAlCrN coating increases. • The excellent oxidation resistance strongly depended on the compact Cr Al rich oxide layer. • The presence of the Cr Al rich oxide layer can limit the rapid diffusion of Ti atoms to the surface. [ABSTRACT FROM AUTHOR]

Adhesive wear is one of the major reasons for the failure of components during various tribological application, especially for rubbing with viscous materials. This study presents CrN/DLC/Cr-DLC multilayer composite coatings prepared on a plasma enhanced chemical vapor deposition (PECVD) device with the close field unbalanced magnetron sputtering ion plating (CFUBMSIP) technique. SEM, XRD and Raman spectroscopy were used to determine the structure of multilayer coatings. It was found that the multilayer coatings are composed by the alternating CrN and DLC layers. Compared with the single CrN coatings, the friction coefficient of the CrN/DLC/Cr-DLC multilayer coating decreases about more than seven times after sliding a distance of 500 m. This helps to reduce the adhesive wear of multilayer coatings. Compared with the single CrN and DLC coating, the wear rate of the CrN/DLC/Cr-DLC multilayer coating is reduced by an order of magnitude to 7.10 × 10 −17 (sliding with AISI 440C) and 2.64 × 10 −17 (sliding with TC4) m 3 /(N m). The improved tribological performance of multilayer coatings mainly attributes to the introduction of lubricant DLC and hard support CrN layers, the enhancement of crack propagation inhibition, and the increment of elastic recovery value W e (71.49%) by multilayer design method. [ABSTRACT FROM AUTHOR]

Fracture toughness is an important characteristic for coatings for high speed cutting of titanium. This study focuses on improving the fracture toughness of the coatings using a layered design method. TiAlN/CrN multilayer coatings with bilayer periods between 12 nm and 270 nm were prepared by reactive magnetron sputtering. XRD results show the multilayer coatings have face-centred cubic structures. When the bilayer period of multilayer coating decreases from 270 nm to 25 nm, the coating hardness decreases from 24.5 GPa to 18.1 GPa. Increased fracture toughness and adhesion strength of multilayer coatings are observed with decreasing bilayer periods. A maximum fracture toughness (K IC ) of 3.6 MPa m 1/2 and adhesion strength of 107 N were obtained with a 25 nm bilayer period. The inhibition of crack propagation is the main reason for the high fracture toughness values in multilayer coatings. However, when the bilayer period is decreased further (12 nm), the coating hardness begins to increase rapidly to 23.4 GPa, and the fracture toughness and adhesion strength begin to decrease. Titanium cutting results show that an improvement in cutting performance is obtained with a TiAlN/CrN_25 multilayer coating. [ABSTRACT FROM AUTHOR]

Adhesive wear is one of the major reasons for short tool life during machining titanium alloys. This study presents a new kind of low adhesive wear TaO functional coating prepared by magnetron sputtering. The composite coating is composed by two layers of a solid solution TiAlTaN in bottom and a TaO (Ta 2 O 5 or TaO x ) on top. Tool life of the TiAlTaN/TaO coatings is increased more than triple the TiAlTaN single coating by titanium cutting experiments. Cutting performance of commercial TiAlN-based coated tool is increased 267% after coating the TaO on the surface. Friction and wear between the coatings and Ti6Al4V counterpart have been conducted. The results show that both the friction coefficient of the coatings (from 1.05 to 0.82) and surface roughness (from 12.2 ± 0.6 to 7.1 ± 0.1 nm) are decreased by increasing TaO thickness from 0 to 150 nm. The adhesive bonds between coating and titanium also reduce with increasing the TaO thickness. This leads to the significantly reduction of the adhesion at the cutting tool tip after coated the TaO coating. This is because that the titanium is not easy to bind with the TaO coating by the calculated positive interaction energy between the Ta 2 O 5 surface and pure Ti. [ABSTRACT FROM AUTHOR]

Phase transformation between bcc and fcc in Fe–Ni nanoparticle has been studied by using molecular dynamics simulation with an embedded atom method. The transformation has been explored by designing the nanoparticles with different initial structures, sizes and elemental distributions at various Ni concentrations. The results show that the structural transformation is strongly related to the Ni content and elemental distribution. Initial fcc structure transforms to bcc for a lower Ni content and bcc transforms to fcc for a higher Ni content. The transformation is accompanied with a sharp reduction in energy even for the nanoparticle with a large size. Furthermore, lattice distortion first occurs before the transformation. The transformation from fcc to bcc is occurred by elongating fcc (100) to bcc (110) and that from bcc to fcc by compressing bcc (110) to fcc (100). The reason is that the nanoparticle has a low energy state for bcc structure with a lower Ni content and also for fcc structure with a higher Ni content. The coexistence of bcc and fcc phases appears with the change of elemental distribution. [ABSTRACT FROM AUTHOR]

Structural evolutions of Co 561 clusters supported on the Cu(010) substrate were studied by molecular dynamics simulation using an embedded atom method. Energy, snapshot, pair distribution function and epitaxial factor were used to analyze the effects of supported position, configuration and temperature on the structural evolutions. It is found that the energy of the cluster changes significantly with varying the supported position and the original configuration. The most stable supported position is (111) facet. As a function of configuration the stability decreases in the order: icosahedron > truncated octahedron > decahedron > cuboctahedron > sphere. Supported (111) facet changes to stack along the (100) of substrate. Epitaxial growth on the substrate occurs for all configurations. The epitaxial temperature and the amount of epitaxial atoms are related to the configuration. The epitaxial growth is adverse to the stability of the cluster, while the epitaxy has no effect on the crystal structure of the supported cluster. The energy of the cluster is reduced by the epitaxial growth and atomic penetration into the substrate but is enhanced by the distortion of the cluster on the substrate. [ABSTRACT FROM AUTHOR]

The formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters has been studied by molecular dynamics simulation using an embedded atom method. Structural evolution of the clusters, coalesced under varying temperature, Ni content and substrate conditions, was explored by interatomic energy, snapshots, pair distribution functions and bond order parameters. The results show that the formation of bcc and fcc is strongly related to Ni content, substrate and coalescence temperature. Free clusters coalesced at 1200 K form bcc at lower Ni contents with fcc forming at higher Ni concentrations and no observable coexistence of bcc and fcc. Differences in coalescence at 1000 K result from the coexistence of bcc and fcc within the Ni range of 50–70%. Free clusters supported on disordered Ni substrates were shown to transform from spherical morphology to islands of supported clusters with preferred epitaxial orientation. The Ni content required to form bcc and fcc coexistence on supported clusters at 1000 K decreased to 30–50% Ni. Free clusters possessing bcc and fcc generally stacked along the bcc (110) and fcc (111) facets, whereas supported clusters stacked along the (111) bcc and (100) fcc planes. Structural transformation was induced by clusters containing greater numbers of atoms. Spread over the substrate enhanced interatomic energy, order substrates affect the epitaxial growth direction and increase the melting points of the supported clusters. This study can be used to predict the nature of fcc and bcc formation in Fe–Ni films. [ABSTRACT FROM AUTHOR]

Fe-based amorphous alloys (FAA) have excellent anti-corrosion and anti-abrasive comprehensive performances. However, sprayed thin FAA coatings with high porosity cannot provide efficient protection, or even accelerate the corrosion rate of the substrate due to galvanic corrosion. Laser re-melting densifying is usually used to improve the anti-corrosion performance of sprayed coatings. There are two disadvantages of the common laser re-melting method, including crystallization and residual stress. In the present paper, a low density energy laser re-melting method was used to improve the performance of cold spraying (CS) FeCoCrMoBCY FAA coating on 40Cr substrate. The results show that the CS FAA coatings were crystallized partially during the melting process. The hardness of the coating is improved at the melting zone after laser re-melting, which improves the anti-abrasive performance. Potentiodynamic test results show that laser re-melting can decrease the corrosion rate, but the salt spray test indicates that low energy density re-melting cannot eliminate penetrated diffusion passage. Further optimization should be conducted to improve the anticorrosion performance for this method. [ABSTRACT FROM AUTHOR]