Running-in Stage Research Articles

Probing the friction mechanism of diamond-like carbon films in aqueous environments based on molecular dynamics simulations

Abstract The frictional behavior of diamond-like carbon (DLC) films in an aqueous environment is of tremendous interest. To compare the impacts of the quantity of water molecules, sliding velocity, and loading on the friction behavior of DLC films, a molecular model of DLC films in an aqueous environment was built. The results show that the DLC film under high load and high sliding velocity leads to severe friction behavior, but the water molecules can prevent the occurrence of this severe friction behavior. Also increasing the number of water molecules can effectively reduce the increase in friction during the running-in stage and keep it at a low value. The primary explanation is that if there are enough water molecules, they will create a stable water film at the friction interface and prevent large-scale contact and distortion between the upper and lower DLC films, significantly reducing friction.

Evolution of Lubrication Characteristics of Double-Nut Ball Screws Based on an Efficient Surface Roughness Modeling Method

Abstract Accurate prediction of lubrication characteristics, specifically film thickness and pressure distribution, is pivotal for ensuring optimal performance in ball screws. Despite its significance, there is a notable dearth of studies investigating the evolution of lubrication characteristics resulting from the changing surface roughness over prolonged operation of ball screws. Furthermore, obtaining the surface roughness of ball screws poses a challenge due to the limited loading capacity of measurement instruments. Traditional methods involving cutting the screw for surface roughness measurement are impractical for continuous monitoring during extended operation. To address this issue, the present study introduces an efficient approach to model the surface roughness of the raceway in double-nut ball screws. A profilometer is employed to measure profile roughness along two directions (parallel and perpendicular to the rolling direction) without the need to cut the screw raceway. The 2D power spectral densities and height probability densities of profile roughness are calculated to model the surface roughness, and the synthesized data are utilized to solve the Reynolds equation. The simulation method is validated through friction torque tests, demonstrating a calculation accuracy exceeding 92%. The study further explores the evolution of film thickness and pressure distribution in double-nut ball screws during running-in and steady wear stages, revealing severe asperity contact in the two nuts. Additionally, variations in load ratio, friction coefficient, and film thickness ratio (λ) are investigated. Considering the load ratio and λ of the slave nut, it can be inferred that boundary lubrication persists in the two nuts throughout the operation.

Full-scale experimental study on tribological performance of FPBs for highway bridges with various solid lubricants under fast loading

Friction pendulum bearings (FPBs) have proven to be effective for the seismic isolation of highway bridges. Previous studies often employed scaled model shaking table tests to investigate dynamic responses of the structures or quasi-static tests to assess the hysteretic performance of FPBs. However, it is noteworthy that the stress on the friction surface is reduced due to the size effect in scaled model in shaking table tests, while quasi-static tests of prototype bearings cannot simulate the sliding velocity experienced during seismic events, which is a sensitive parameter for the performance of FPBs with solid lubricant plates. Research on the performance of full-scale FPBs under fast frictional loading is very limited. This paper addresses this knowledge gap by studying the velocity demand for a highway bridge with FPBs and conducting fast sliding performance tests using full-scale FPBs. The results indicate that under a 0.2 g PGA earthquake, the velocity demand for FPBs can reach 0.5 m/s. Through testing full-scale FPBs at various loading speeds, it was found that solid lubricant plates by UHMWPE material exhibit poor thermal stability during wear tests, solid lubricant plates by PTFE material lack sufficient tangential tear strength under fast loading, and solid lubricant plates by PET material show good wear resistance but have a high breakaway force and levered maximum force during the running-in stage. Subsequently, this study developed ultra-high performance friction plate (UHPF) as the solid lubricant for FPBs, achieving ideal hysteretic performance under fast loading. The full-scale FPB specimens in this paper are the ones manufactured for the continuous beam bridges in the Shenzhen-Zhongshan Sea-crossing Link project in China. The dimensions of the bearing, axial load, and loading speed is much more stringent than those in previous FPB tests, providing results that are highly important for engineering applications.

Wear prediction of high performance rolling bearing based on 1D-CNN-LSTM hybrid neural network under deep learning

The finished precision rolling bearings after processing are required to pass the life test before they can be put into the market. The life testing takes a lot of time and expense. Aiming to solve the problem of time and expense, the 1D-CNN and 1D-CNN-LSTM hybrid neural networks are used for deep learning based on the existing rolling bearing life big data results (a total of 791152 date). Taking the wear of bearing as the target, the life prediction of bearing is carried out by using Python. The results show that: (1) 1D-CNN-LSTM algorithm and "all parameters” are selected as the best prediction options. (2) "XYZ direction displacement” and "all parameters” have the best fitting effect on the predicted wear value, and the MAPE is 4.18877, 1.2102, 2.68903 and 1.19981, respectively. The 1D-CNN-LSTM algorithm is slightly better than the 1D-CNN algorithm. (3) Using 1D-CNN-LSTM algorithm and "all parameters” to predict the bearing wear life will obtain good results. Compared with the highest 1D-CNN and "Four Bearing Temperatures” parameters, it is reduced by 14.7 times. (4) The prediction process and results provide a wear prediction method for relevant bearing enterprises in the experimental running-in stage. It can also provide reliable research ideas for subsequent related enterprises and scholars.

The Role of Triboloading Conditions in Tribolayer Formation and Wear Resistance of PES-Based Composites Reinforced with Carbon Fibers.

In this paper, the tribological characteristics of polyethersulfone-based composites reinforced with short carbon fibers (SCFs) at aspect ratios of 14-250 and contents of 10-30 wt.% are reported for linear metal-polymer and ceramic-polymer tribological contacts. The results showed that the wear resistance could be greatly improved through tribological layer formation. Loading PES with 30 wt.% SCFs (2 mm) provided a minimum WR value of 0.77 × 10-6 mm3/N m. The tribological layer thicknesses were estimated to be equal to 2-7 µm. Several conditions were proposed, which contributed to the formation of a tribological layer from debris, including the three-stage pattern of the changing kinetics of the time dependence of the friction coefficient. The kinetics had to sharply increase up to ~0.4-0.5 in the first (running-in) stage and gradually decrease down to ~0.1-0.2 in the second stage. Then, if these levels did not change, it could be argued that any tribological layer had formed, become fixed and fulfilled its functional role. The PES-based composites loaded with SCFs 2 mm long were characterized by possessing the minimum CoF levels, for which their three-stage changing pattern corresponded to one of the conditions for tribological layer formation. This work provides valuable insight for studying the process parameters of tribological layer formation for SCF-reinforced thermoplastic PES composites and revealing their impact on tribological properties.

Regulating the severe running-in wear of polymer composites by a dual-pin-on-disk (DPOD) multicomponent approach

Polymer composites are increasingly used as frictional components due to their self-lubricating properties. However, they tend to exhibit severe wear during the running-in stage, thus significantly impairing their service life. In the present work, a dual-pin-on-disk (DPOD) method is developed in order to reduce the running-in wear of a polytetrafluoroethylene/alumina (PTFE/Al2O3) composite when sliding against GCr15 bearing steel by introducing an assistant polymer component during the running-in stage. The results show that the running-in wear rate of the main polymer pin is reduced by up to 77.26 %. This is because the assistant pin causes excess wear debris to be released into the wear track and provides a higher shear force, thereby promoting the tribological chemical reactions and facilitating the generation of tribofilms on the worn surfaces. In addition, the processed polymer achieves a wear rate similar to that of the conventional single pin condition (∼3 × 10−7mm3/Nm) in the subsequent steady-state stage. The results of the present work are expected to increase significantly the wear life span and application prospects of the polymer composites.

Spatio-temporal Evolution and Coordinated Development of Compactness with Carbon Emission Intensity in the Chengdu-Chongqing Urban Agglomeration

Studies on the spatio-temporal variation and coordinated development level of compactness with carbon emission intensity in the Chengdu-Chongqing urban agglomeration is of great significance to achieve green, low-carbon, and high-quality development of society. The spatial-temporal differentiation, coupling coordination, and driving factors of the compactness and carbon emission intensity of the Chengdu-Chongqing urban agglomeration from 2010 to 2020 were analyzed by using the methods of comprehensive evaluation, carbon emission identical equality, coupling coordination, and the Geo-detector model. The results showed that:① The compactness of the Chengdu-Chongqing urban agglomeration continued to rise from 0.18 in 2010 to 0.22 in 2020, with an overall increase of 22.22 %, in which the contribution rate of economic compactness to urban compactness increased yearly. There were significant regional differences in the compactness of cities. The high-value areas were concentrated in Chengdu, Deyang, and Mianyang in the northwest and Zigong, Neijiang, and Luzhou in the southwest, whereas the low-value areas were distributed in the middle. Ya'an was always the area with the lowest compactness of urban agglomeration. ② The carbon emission intensity of the Chengdu-Chongqing urban agglomeration was decreasing yearly, with a decrease rate of 39.57 % during the study period. The carbon emission intensity in the southern part of the urban agglomeration was higher than that in other regions as a whole, whereas Chengdu and Chongqing were low-value areas all the year round, and the regional differences of carbon emission intensity were gradually narrowing. ③ The coupling degree between urban compactness and carbon emission intensity changed from the antagonistic stage to the running-in stage; the coupling coordination degree increased notably, from 0.21 in 2010 to 0.69 in 2020; and the two systems gradually moved towards benign and coordinated development. The coupling coordination between the northwest of the urban agglomeration (Chengdu, Deyang, and Mianyang) and the south of Sichuan (Zigong and Luzhou) was generally high. Industrial structure, scientific and technological innovation, urbanization level, government intervention, and environmental livability all had significant effects on the coupling and coordination of the two systems. ④ Optimizing industrial structure, strengthening scientific and technological support, improving the quality of urbanization development, implementing active policy guidance, and building green barriers were effective ways to promote the coordinated development of compactness and low carbon in the Chengdu-Chongqing urban agglomeration.

Influence of Interfacial Tribo-Chemical and Mechanical Effect on Tribological Behaviors of TiN Film in Different Environments

A series of experiments has been conducted to investigate the tribological properties of a TiN film sliding against GCr15 steel balls in ambient air, low vacuum and high vacuum environments. Various friction loads and sliding velocities were also applied. The TiN film displays a steady-state friction stage after the running-in stage in all the above environments, while the durations of running-in stages are different. The steady-state friction coefficients of the TiN film were around 0.56 in ambient air and 0.3 in the high vacuum environment (1 × 10−5 mbar). In the low vacuum (1 × 10−2 mbar) environment, a low friction coefficient (around 0.19) was attained for all the friction tests on TiN film, irrespective of the applied load and sliding velocity. In the meantime, it was noticed that the applied loads and the sliding velocities would change the duration of the running-in stage before reaching the low friction coefficient. It is revealed by the analysis of wear tracks that the metal oxides induced by the tribo-chemical effect at the friction interface play an important role in affecting the tribological behaviors of the TiN films in different environments. The Raman results show that the main component of the metal oxides is hematite (α-Fe2O3), and the amount of iron oxide is related to the friction environment. The composition and quantity of iron oxides produced by the interfacial tribo-chemical effect affect the tribological behavior. The results also show that the mechanical wear process at the friction interface displays a polishing effect, which would reduce the surface roughness. The mechanical wear performance varies under different loads and velocities. The tribological tests results indicate that the interfacial tribo-chemical effect and mechanical wear process should be considered together rather than individually to interpret the tribological behaviors of TiN films in different environments.

Dual in-situ observation of tribochemical and morphological evolution of single-layer WS2 and multi-layer WS2/C coatings

The outstanding tribological performance of transition metal dichalcogenides (TMDs) is attributed to their unique sandwich microstructure and low interlayer shear stress. This advantageous structure allows TMDs to demonstrate exceptional friction reduction properties. Furthermore, the incorporation of TMDs and amorphous carbon (a-C) in multi-layer structures shows excellent potential for further enhancing tribological and anti-oxidation properties. Amorphous carbon, known for its high ductility, chemical inertness, and excellent wear resistance, significantly contributes to the overall performance of these multi-layer coatings. To gain an in-depth understanding of the tribological mechanism and evolution of TMDs’ multi-layer coatings, a dual in-situ analysis was carried out using a tribometer equipped with a 3D laser microscope and a Raman spectrometer. This innovative approach allowed for a comprehensive evolution of the tribological, topographical, and tribochemical characteristics of both single-layer WS2 and multi-layer WS2/C coatings in real time. The findings from the dual in-situ tribotest revealed distinct failure characteristics between the single-layer WS2 coating and the multi-layer WS2/C coating. The single-layer WS2 coating predominantly experienced failure due to mechanical removal, whereas a combination of mechanical removal and tribochemistry primarily influenced the failure of the multi-layer WS2/C coating. The tribological evolution process of these two coatings can be classified into four stages on the basis of their tribological behavior: the running-in stage, stable friction stage, re-deposition stage, and lubrication failure stage. Each stage represents a distinct phase in the tribological behavior of the coatings and contributes to our understanding of their behavior during sliding.

Research on the coordinated development of provincial urbanization and carbon emission efficiency of construction industry in China

BackgroundEnergy conservation and emission reduction policies restrict the economic and social development of all countries in the world, and the impact on China, which has low urbanization, is more serious. In the process of promoting urbanization, the pressure of carbon emission reduction in the construction industry has increased, and the high emissions of the construction industry have made the low-carbon development of cities face severe challenges. China is at a critical stage of urbanization development, and there is become a general consensus on how to improve the carbon emission efficiency of the construction industry. The interaction between urbanization and the carbon emission efficiency of the construction industry is a long-term and complex process. As one of the industries contributing to China’s urbanization process and carbon emissions, it is of great practical significance to explore the coordination relationship between urbanization and the carbon emission efficiency of the construction industry (CEECI) to realize the goal of “double carbon”, promoting urbanization construction and solving the problem of “green development”. Taking 30 provinces in China as the research target area, the double weighted summation method and the undesirable output superefficiency window-EBM-DEA model are used to measure the provincial urbanization level and CEECI, respectively. Then, the coupling coordination degree model of the relative development index is introduced, and the spatial autocorrelation model and the spatial and temporal differentiation characteristics of the coordination level of urbanization and the CEECI are analysed.ResultsFrom 2010 to 2021, China’s urbanization level increased steadily, but the growth rate gradually decreased. There were significant differences in urbanization levels among provinces. The eastern provinces have a higher level of urbanization but lack an impetus in the later period, while the western provinces have a lower level of urbanization but a faster growth rate. The low-carbon development trend of China’s construction industry is good, and the overall development of the CEECI shows an “N” type, and the inflection points appear in 2013 and 2018. The interprovincial urbanization level is significantly different from that of the CEECI, and the development form of the central and western provinces is better than that of the eastern provinces. The coordination level of urbanization and the CEECI in China is transitioning from the running-in stage to the coordination stage, and the coupling coordination degree between systems is on the rise, while the relative development degree is on the decline. The spatial distribution pattern is in a dynamic state of change, and the overall distribution pattern is “high in the east and low in the central and western regions”. The differences among provinces were significantly decreased, with 63.33% of provinces at the high running-in level. The provinces that entered the coordination stage were mainly located in the eastern region, and only Beijing was in the coordination stage by the end of the study. In addition, 90% of the provinces exhibited lagging efficiency, and only Jiangxi, Guangxi and Chongqing, which had low coordination levels maintained synchronous development of the two systems. The coordination level between provincial urbanization and the CEECI showed a positive spatial distribution, the global Moran index showed a “V” shape trend, and the spatial dependence of the coordination level between the two systems gradually weakened. In the local spatial distribution, there are two types of convergence: high and low.ConclusionsThe coordination degree of urbanization and the CEECI analysed in this study is an extension of the research on the relationship between the two. By integrating the two into a unified framework, the method of combining quantitative and qualitative analysis is used to further explore the coordination relationship between the two, which not only enhances the scientificity and accuracy of the research but also extends the breadth and depth of relevant theoretical research. At the same time, according to the coordination type between urbanization and the CEECI, China should propose corresponding targeted coordination and optimization paths from the perspective of urbanization and low-carbon development of the construction industry to achieve high-quality development of China’s economy and society.

Degradation modeling and reliability estimation for mechanical transmission mechanism considering the clearance between kinematic pairs

The mechanical transmission mechanism is the core component of electromechanical systems, of which the health state can affect the accuracy and stability of the entire system. Due to machining errors and thermal deformation, clearance often exists between the kinematic pairs, which leads to irregular collision- separation during the operation. The clearance size and the surface quality of pairs change during the service life, leading to the time-varying damage and degradation state of the mechanism. Therefore, the kinematic pairs suffer from not only natural deterioration process such as wear, fatigue, etc., but also the collision-separation process caused by the clearance. In this paper, a degradation and shock model for the mechanical transmission mechanism is proposed considering the influence of clearance between the kinematic pairs. The degradation process is divided into running-in stage, stable degradation stage, and fast degradation stage according to the health states, and is modeled by a transformed gamma process to account for the dependency between service time and health state. Random shocks caused by the collision-separation process are classified into different zones in terms of their sizes, and the arrival rate of the shocks also change with the health state of the mechanism. The closed-form reliability function is derived and verified by the experiment of rotating pair of the crank and rocker mechanism. Results show that the proposed degradation and shock model can obtain a more realistic and reasonable reliability of the transmission mechanism.

High temperature lubrication performance of chlorophenyl silicone oil

Most studies of liquid lubricants were carried out at temperatures below 200 °C. However, the service temperature of lubricants for aerospace and aeroengine has reached above 300 °C. In order to investigate the friction mechanism and provide data for high temperature lubrication, the friction and wear properties of chlorophenyl silicone oil (CPSO)-lubricated M50 steel and Si3N4 friction pairs were investigated herein. Ball-on-disk experimental results show that the lubrication performance of CPSO varies significantly with temperature. Below 150 °C, coefficient of friction (COF) remains at 0.13–0.15 after the short running-in stage (600 s), while the COF in the running-in stage is 0.2–0.3. At 200 °C and above, the running-in time is much longer (1,200 s), and the initial instantaneous maximum COF can reach 0.5. Under this condition, the COF gradually decreases and finally stabilizes at around 0.16–0.17 afterwards. This phenomenon is mainly due to the different thickness of boundary adsorption film. More importantly, the wear rate of M50 steel increases significantly with the temperature, while the wear rate barely changes at temperatures above 200 °C. The anti-wear mechanism is explained as tribochemical reactions are more likely to occur between CPSO and steel surface with the increased temperature, generating the FeCl2 protective film on the metal surface. Accordingly, FeCl2 tribochemical film improves the lubrication and anti-wear capacity of the system. At high temperatures (200–350 °C), FeCl2 film becomes thicker, and the contact region pressure becomes lower due to the larger wear scar size, so the wear rate growth of M50 steel is much smaller compared with that of low temperatures (22–150 °C). The main findings in this study demonstrate that CPSO lubricant has good anti-wear and lubrication capacity, which is capable of working under temperatures up to 350 °C.

RESOURCE-SAVING RUN-IN OF INTERNAL COMBUSTION ENGINES
 AT USE OF OIL MODIFYING ADDITIVES

Using the example of the cold stage of running-in of a D-245 diesel engine on a running-brake stand KI-2139B
 at a crankshaft speed of the engine being run in within 700±10 min–1, it was established that the use of additives to lubricating
 oils allows reducing the break-in time by 1,5 times. Cold running-in of diesel engines at a repair facility using
 M-10G2 oil with the SURM KV additive containing 3,2–3,4% at a supply oil temperature of 55–65 °C requires a duration
 of 60 minutes. The use of the SURM KV additive makes it possible to obtain compression pressures during cold
 running that are the same as during hot running at idle using the basic technology. The exclusion of the hot running-in
 mode at idle speed from the technological process of running-in diesel engines is justified. The economic effect of introducing
 special additives into the lubricant during running-in of internal combustion engines is to reduce its time and
 reduce fuel consumption.

Enhanced high-temperature tribological performance of fluorinated tetrahedral amorphous carbon (ta-C:F) coatings in sliding applications

This study investigated the dry sliding behaviour of fluorinated tetrahedral amorphous carbon (ta-C:F) coatings against uncoated 52100 steel at temperatures ranging from 25 °C to 300 °C. The ta-C:F coatings demonstrated significant reductions in both the coefficient of friction(COF) during the running-in stage and at steady state, particularly within the temperature range of 25 °C to 200 °C, surpassing the performance of well-established a-C:H coatings. SEM analyses revealed the formation of transfer layers on the contact surface of 52100 steel when tested against ta-C:F coatings at temperatures up to 200 °C, while none were detected at temperatures ≥250 °C. Raman spectroscopy indicated a transition from sp3 to sp2 carbon structures in the carbonaceous transfer layers with increasing temperature, and XPS scans confirmed an increase in fluorine (F) concentration within these layers, correlating with reduced COF. The comparative analysis at 120 °C emphasized the intrinsic advantages of ta-C:F coatings in high-temperature applications, demonstrating a nearly 50% lower COF (0.08) when compared to traditional boundary-lubricated steel-to-steel sliding contacts. These findings have significant implications for enhancing the efficiency and durability of various mechanical systems, particularly in industries like automotive and manufacturing.

Robust macroscale superlubricity of multiple base oils achieved on soft epoxy resin coatings

Reducing the friction of base oils to a superlubricity state is highly expected at engineering scale. However, it still is a great challenge for the most of viscous base oils to achieve superlubricity on the conventional tribopairs up to now. Here we report the strategy of solid-oil composited lubrication constructed with an ultra-smooth epoxy resin (EP) coating and base oils for achieving superlubricity. Especially, the frictional results showed that the proposed strategy in this study could be suitable for multiple base oils, including nonpolar and polar base oils as lubricants. The friction coefficient of steel/EP tribopair lubricated by the base oils containing hydroxyl group can be as low as 0.001. Meanwhile, the composited lubrication system did not undergo an obvious running-in stage to achieve the superlubricity state regardless of the type of base oils. The surface hydroxylation of the steel counter ball sliding against EP coating was observed by time-of-flight secondary ion mass spectrometer, even when lubricated by nonpolar base oils without hydroxyl group. This could be a critical factor for the base oils to achieve superlubricity. This finding provides a new and facile approach to realize robust superlubrication for different base oils at engineering scale.

A running-in strategy based on an efficient wear simulation model for double circular-arc spiral bevel gears

A proper running-in process is necessary for double circular-arc spiral bevel gears to achieve desirable meshing performance. However, this type of gear transmission lacks a suitable running-in wear model, which brings great difficulties to the design of appropriate running-in strategies. To address this problem, the present study establishes an efficient numerical wear model to reveal the wear behavior of double circular-arc spiral bevel gear pairs, based on which a step-wise load running-in strategy is proposed. The established Archard's wear model considers the meshing characteristics of double circular-arc spiral bevel gears and sets a small threshold value, which can reflect the wear behavior of this gear in the running-in stage. To improve the computation efficiency, a two-step parameter updating strategy is proposed to enhance the iteration of p and s. The wear simulation reveals the quantitative relationship contact pressure and running-in cycle during the running-in process. Based on the reveal relationship, a step-wise load running-in strategy is proposed to sharpen the running-in period. The developed wear model and the proposed running-in strategy can be extended to other types of gears with circular-arc profiles.

Features of Tribooxidation of the High-Entropy Coating (AlCrZrTiTa)N during Dry High-Speed Cutting

The high-entropy PVD coating (AlCrZrTiTa)N, characterized by its high hardness (50–60 GPa), elastic modulus above 300 MPa, and high heat resistance up to 1300 °C, is used for coating cutting tools operating under extreme metalworking conditions. The nanostructured monolayer 3 μm PVD coating was deposited on cutting plates in the hybrid arc deposition PVD coater. The coating had an amorphous nanocrystalline microstructure with a grain size of about 10–50 nm. The samples of SS 304 steel were investigated during dry high-speed (600 m/min) cutting. Raman spectroscopy was used to study the formation of tribooxides on the tool surface at the running-in stage of the cutting. After 130 m of cutting, Cr2O3 oxide appears on the wear surface while other elements are bound with N atoms. When the cutting length is increased to up to 260 m, oxide Al2O3 · ZrO2 (mullite) and amorphous oxides TaO2 and CrO2 are formed. The method EELFS made it possible to determine the amorphous nanocrystalline structure of triboceramics based on CrO2 and Al2O3 · ZrO2. The nearest atomic surrounding of Cr-Cr, O-O, and Cr-O and their subsequent comparison with the available literature data allow us to calculate the equilibrium lattice constants of the CrO2 unit cell, which are equal to (a, b) = 4.3754 Å and c = 0.5927. The triboceramic films on the base of non-equilibrium mullite Al2O3·ZrO2 have an amorphous structure. In the first coordination sphere, the interatomic distances of Zr-O and Al-O were 1.79 and 1.89 Å. An accelerated adaptive reaction to extreme external stimuli, at the very beginning of the running-in stage, is established. The tribological adaptability of the high-entropy ultra-fine amorphous nanocrystalline coating under extremely loaded dry high-speed cutting is based on non-equilibrium phenomena: the partial oxidation of fragments of the nitride and dynamic formation of protective tribooxides, which have a good thermal barrier and frictional properties. These factors interact synergistically and determine the life of the cutting tool.

Research on the Coordinated Development of Technological Innovation,Talent Agglomeration, and New Urbanization in the Yangtze River Economic Belt

In the context of high-quality development, the development paradigm of integrating scientific and technological innovation, talent agglomeration, and new-type urbanization has become a key issue in regional development. Taking the Yangtze River Economic Belt as an example, this paper analyzes the interaction mechanism of the three systems and constructs an evaluation index system from the perspective of regional high-quality development. This paper combined entropy weight TOPSIS, coupling coordination degree model, and Gini coefficient to explore the spatial and temporal characteristics and regional differences of system coupling coordination. The evolution trend of the coupling coordination type is predicted by the Markov chain model. The research shows that: (1) The development index of the three major systems in the Yangtze River Economic Belt is on the rise, and the coupling coordination degree is in the running-in stage as a whole. The resistance restricting the coupling coordination degree is mainly the lag of scientific and technological innovation in the upstream, and the lag of talent gathering in the middle and downstream. ( 2) The coupling coordination degree of the three systems has obvious spatial agglomeration characteristics, showing a high level in the lower reaches of the Yangtze River, and a low level in the middle and upper reaches of the Yangtze River. (3) The gap of the coupling coordination degree of the three systems in the whole Yangtze River Economic Belt is gradually narrowing, and the large development gap among different regions is still the main cause of the Gini coefficient of the Yangtze River Economic Belt. (4) There is a location difference in the probability of coupling coordination level transfer, and the upper and middle reaches of the Yangtze River will still be in the antagonistic or running-in stage in the next stage, while the lower reaches of the Yangtze River will be in the coordination stage. The research conclusions provide scientific references for the high-quality development of the Yangtze River Economic Belt.

Effect of modifiers on the structure formation and properties of nickel-phosphorus coatings applied to powder steels

The paper shows the effect of solution temperature on the deposition rate of applying composite nickel-phosphorus coatings modified with boron nitride and polytetrafluoroethylene to powder samples made of improved P40, P40Kh and P40KhN steels obtained by hot stamping of porous sintered blanks. It has been experimentally established that within the range of 70–90 °C, the average deposition rate of modified BN and (C2F4)n coatings is 15–19 μm/h, while the chemical composition of the improved steels and the surface configuration of the samples have no effect on the coating build-up rate. The mechanism of the formation of the structure and properties of nickel-phosphorus coatings (NiPC) without additives and those of NiPC modified with boron nitride and polytetrafluoroethylene during deposition, sintering and running-in is revealed. It has been established that immediately after deposition, Ni–P coating has an amorphous structure with inclusions of nickel particles, and its microhardness does not exceed 380–390 MPa with no modifiers added. In the dry friction mode at the running-in stage, Ni12P5 and Ni2P phases are formed in the modified Ni–P coatings, allowing to improve their tribological properties, and in the steady-state mode, the phase disordering of the modified NiPC proceeds. It has been experimentally revealed that the coefficient of friction and wear decrease by 1.3 times when only (C2F4)n is introduced into Ni–P coating, these indices decrease by 1.6 times when only BN is added, and they decrease almost twice when BN and (C2F4)n are introduced together. It has been established that upon the combined (complex) modification of NiPC with BN and (C2F4)n after the heat treatment, there is almost no nickel oxide phase, nickel boride of NiB type is formed in the coating during running-in, and its content does not decrease when entering the stationary friction mode, thus increasing tribotechnical properties of the coating. During running-in, the coefficient of friction of Ni–P + BN + (C2F4)n coating decreases from 0.28 to 0.19, and the wear rate of such a coating in the stationary friction mode is 1.5 mg/h. The efficiency of applying the antifriction nickel-phosphorus coatings modified with BN + (C2F4)n to the products made of the improved structural steels obtained by various methods has been theoretically and experimentally substantiated.

Monitoring Wear of a Deep Groove Ball Bearing Using Ultrasonic Reflection

Abstract Wear changes the contact state and contact stiffness of the interface between the ball and the outer raceway under the operation of a deep groove ball bearing, resulting in the change of reflection coefficient of the interface. This paper describes a method based on ultrasonic reflection to assess the wear status of rolling element bearings. A deep groove ball bearing wear test was performed and the reflected pulses were collected with a linear ultrasonic probe mounted on the bearing outer ring. The results show as the wear intensity first increases and then decreases from running-in stage to steady wear period, the reflection coefficient of the interface between the outer raceway and ball shows the expected opposite trend. In addition, the ultrasonic measurement of wear state was verified by oil debris monitoring using on-line visual ferrography.