Average Friction Coefficient Research Articles

Analysis of thermal behavior and mass transport for manufacturing deep-small hole by ultra-high frequency induction-assisted laser wire deposition

Synchronous ultra-high frequency (UHF) induction-assisted laser deposition is an effective approach to tackle the extreme heat input and common defects that originate from laser direct deposition. The added auxiliary induction heat source can reduce the energy input of the laser heat source which guarantees the geometric integrity of the embedded tube and decreases temperature gradient. Meanwhile, the effective preheating of the induction heat source assures the metallurgical bonding among the substrate, deposited track and embedded tube. Experiments showed that the effective bonding can be formed among substrate-deposited track and deposited track-embedded tube under suitable combination parameters of the laser heat and induction heat. To gain insight into the hybrid deposition, a 3D numerical model coupled with multi-physical fields was established to explore the thermal process and flow behavior with assistance of induction heat. Results indicated that the electromagnetic force produced by induction coil promotes the flow velocity, which increases heat convection. Investigation on the induction heat parameter demonstrated that raising current intensity can accelerate the flow velocity from 0.07 m s-1 to 0.09 m s-1 while the maximum temperature of the molten pool declined from 2610 K to 2440 K owing to the reinforced heat convection. The experimental cross-section of the deposited tracks and the detected element distribution in transition areas are well tested against the numerical simulation results. The grain size in the top region of the deposited track is refined with increasing current intensity, which is experimentally and numerically verified by observed microstructure and G*R value. Meanwhile, the fabricated deposited track with average friction coefficient of 0.445 can be obtained when the laser and induction parameters are 1000 W and 400A, respectively.

Influence of triangular texture composite MAO coating on the tribological properties of aluminum alloys

To compensate for the poor friction and wear performance of aluminum alloys, in this study, four triangular textures with different area occupancy rate (5.16 %, 9.17 %, 20.63 % and 28.07 %) were prepared on the surface of aluminum alloys by laser texture technology, subsequently micro-arc oxidation (MAO) coatings were prepared using MAO technique. The treated samples were characterised by X-ray diffraction, micro-morphological analysis, optical profiler and energy dispersive spectroscopy. The tribological performance under oil lubrication conditions was tested by using a pin-disc contact rotational friction wear tester. The results showed that the sharp corners at the edges of the texture caused current concentration, which resulted in more intense sparking and accelerated MAO growth, thus creating more pores and roughening the surface of the coating. In terms of tribological performance, the triangular texture with 9.17 % area occupancy rate showed the best tribological performance before MAO coating, compared with the substrate, the average friction coefficient decreased by 64.11 %; and after the MAO coating was applied, the triangular texture composite MAO coating with 9.17 % area occupancy rate still had the best tribological performance, and its average friction coefficient further decreased compared with that of the smooth MAO coating by 33.07 %. The analysis suggests that the texture can store abrasive particles to prevent the MAO coatings from being worn through, leading to coating failure, while the hard MAO coatings can resist contact stresses well enough to prevent the texture from being flattened, leading to the failure of the function of storing abrasive debris. Therefore, the integration between texture and MAO coating can greatly enhance the anti-wear properties of aluminum alloys.

Experimental investigation of stick-slip behaviors in dry sliding friction

Friction-induced vibration, particularly the bothersome stick-slip behavior, is a significant contributor to machine damage and component failure. In this study, the vibrational displacement, sound pressure, and coefficient of friction (COF) of several metal or alloy samples in dry conditions are tested using a reciprocating friction force test apparatus. It is found that the stick-slip behavior is more likely to occur at low sliding speeds and high normal loads. Furthermore, under the same working conditions, increasing the surface roughness of the sample or enhancing the hardness difference between the sample and the counterpart can mitigate the stick-slip behavior during the friction process. By analyzing the characteristic parameters of the stick-slip behavior, it is found that the temporal period and the stick-time decrease significantly with an increase in relative sliding speed. Additionally, the amplitude and intensity of the friction-induced noise increases with the increase of the relative sliding speed and normal load. The frequencies of the sound pressure are primarily concentrated around the natural frequency of the frictional system. Finally, we extract the COF and find that the average COF as well as the maximum and minimum COF first decreases sharply, and then becomes stable with the increase of the relative sliding speed due to the transition of friction state from stick-slip behavior to smooth sliding.

Effect of the Laser Cladding Parameters on Microstructure and Elevated Temperature Wear of FeCrNiTiZr Coatings.

In order to prepare coating with good friction and wear resistance at elevated temperature on the surface of hot-working tool steel, by using a CO2 laser, FeCrNiTiZr high-entropy alloy coating with different laser scanning speeds (360, 480 and 600 mm/min, respectively) was successfully fabricated by using laser cladding technology on the surface of H13 steel in this paper. Phase constitutions, microhardness, microstructure, and wear characteristics of FeCrNiTiZr coatings under different laser scanning speeds were analyzed. It was determined that 480 mm/min was the optimal laser scanning speed. The results showed that the coating at the scanning speed of 480 mm/min consists of a BCC phase with significant lattice distortion and high dislocation density; the crystal structure is cellular crystal and dendrite crystal. The coating demonstrates the highest microhardness (842 HV0.2), which is 4.2 times that of the substrate (200 HV0.2). Its average friction coefficients at room temperature and 823 K are approximately one-seventh and one-third of the substrate's, respectively, and its wear volume is reduced by about 98% and 81% under these conditions. Compared to the substrate, the coating underwent slight abrasive wear, adhesive wear, and oxidative wear at both room temperature and 823 K. In contrast, the substrate underwent severe abrasive wear, adhesive wear, oxidative wear, and even fatigue wear.

Tribological properties of perfluoropolymer fiber filled carbon fiber/polyphenylene sulfide composites: Effect of in‐situ fibrillated fiber or split fiber

AbstractIn this study, carbon fiber (CF) filled polyphenylene sulfide (PPS) composites are lubricated with perfluoropolymer (PFP) fiber by melt‐blending. The effect of double fibers (CF‐PFP fibers) on the tribological properties of PPS composites has been carefully investigated and correlated under various sliding conditions. The results indicated that the tribological performance of PPS composites with double fibers is better than that of the composites with a single fiber, especially under severe conditions. Mechanism exploration suggests that a double‐fiber hybrid structure between a hard CF and a soft PFP fiber could tightly entrap the CF by fibril entanglement, thus preventing the CF from being stripped out of the matrix under the steel ring shearing force. Under optimized conditions, the average friction coefficient of composites with PFP fiber is only about 0.1 at 300 N load under 200 rpm, even lower than half of the average friction coefficient of the composites with PTFE powder under the same condition. Notably, compared to commercial split PFP fibers, the in‐situ formed PFP fibers with more uniform distribution significantly improve the tribological properties. This work open up a novel perspective for improving the tribological performance of composites by systematically regulating the microstructure of self‐lubricating fibrous additives.Highlights PFA is subject to in‐situ fibrillation during melt blending. Fibrous PFP effectively improves the tribological properties of PPS/CF composites. The in‐situ formed PFP fiber contributes to better tribological properties. The double‐fiber hybrid structure prevents the CF from being sheared out. The number of processing cycles affects the tribological properties.

Synchronous ultrasonic impact assisted laser cladding CoCrFeNiMo high entropy alloy coating: Microstructure and wear property

Synchronous ultrasonic impact treatment (UIT) is proposed to enhance the microstructure and wear property of laser cladded CoCrFeNiMo high entropy alloy (HEA) coatings on 45 steel. FCC phase with minor tetragonal σ phase and rhombic η phase are form in both conventional and UIT treated coatings. Due to the plastic deformation and high-frequency vibrations induced by UIT, dislocation interactions lead to recrystallization process at the top region coating. With the application of UIT, the columnar grains at top region of the coating transform into fine equiaxed grains owing to recrystallization. The fragmentation of dendrites occurs in the middle region of the coating, resulting in reduced dendrite arm spacing. The results also show the defects, such as pores and microcracks, are effectively eliminated within the coating. Microhardness and wear property of the coating are remarkably enhanced owing to fine-grain strengthening and second-phase strengthening. The average friction coefficient decreases from 0.56 for the conventional sample to 0.49 for the UIT treated sample, and the wear mechanism evolved from a combination of abrasive, fatigue, and oxidized wear to predominantly fatigue and oxidized wear. It indicates that synchronous ultrasonic impact assisted laser cladding is a potential method to fabricate high-performance HEA coatings.

Comparative Study on the Performance of Gel Grease for High-End Equipment Based on the Synergistic Effect of Friction-Reducing Agents.

In the field of high-end equipment, the synergistic effect of friction-reducing agents plays an important role in the performance study of gel grease. Exploring its tribological and rheological properties can not only significantly reduce the coefficient of friction of mechanical components and enhance its viscosity at high temperatures but also effectively reduce energy consumption, thus improving the service life of high-end equipment. In this study, Schaeffler Load 460 gel grease was mixed with polysiloxane viscosity modifier (PV611) and molybdenum dialkyl dithiocarbamate (RFM3000) according to (3:1, 1:1, and 1:3), and its tribological properties and rheological properties were investigated by the MRS-10G friction and wear tester, MCR302 rotational rheometer, and crossover test. Comparative analyses of tribological and rheological properties were carried out. The results showed that the average coefficient of friction of Schaeffler Load 460 grease was reduced by 57.2%, 60%, and 71.9%, respectively, with the addition of two different ratios of friction reducers; the average diameter of abrasive spots was reduced by 44.5%, 55.4%, and 61.3%; and the shear stress and viscosity were increased by 117.94 Pa and 1295.02 mPa∙s, respectively, compared with that of the original grease, which is a good example for the lubrication of gel grease in the high-end equipment industry. This study provides a new direction and idea for the lubrication research of gel grease in the high-end equipment industry.

Comparison of the Braking Behavior Among Cast Steel, Carbon/Carbon (C/C) and Carbon/Carbon-Silicon Carbide (C/C-SiC) Materials Mated with Copper-Based Composites

Carbon-based materials (e.g., carbon/carbon [C/C] and carbon/carbon-silicon carbide [C/C-SiC] materials) are considered promising brake disk materials for high-speed trains to replace cast or forged steels. Investigating the braking behavior of copper-based composites paired with various counterpart materials is helpful in advancing the development of high-speed and lightweight brake systems. In this study, the braking behavior and wear mechanisms of a novel copper-based composite mated with cast steel, C/C and C/C-SiC materials were investigated. The average coefficients of friction for the copper-based composite against C/C and C/C-SiC materials are increased by approximately 16.5% and 6.7%, and the wear rates of the copper-based composite against C/C and C/C-SiC materials are reduced by about 25.9% and 33.9% in comparison to those of the copper-based composite against cast steel. Additionally, compared with that of cast steel, the wear rate of the C/C material is increased by more than 3 times, and the negative value of the wear rate of the C/C-SiC material is noted. The dominant wear mechanisms of the copper-based composite mated with cast steel, C/C and C/C-SiC materials are adhesive wear combined with oxidation, graphite loss combined with oxidation as well as exfoliation of the material near graphite, and the material transfer combined with oxidation, respectively.

Effect of Cu content on the microstructure and properties of sintered Fe-0.8C-xCu antifriction materials

Abstract Ferrous antifriction materials (FAMs) play a crucial role in powder metallurgy. Previous studies have primarily focused on exploring the antifriction properties of Fe-C-Cu materials with low copper content (0–5 wt%), while there have been fewer studies on high copper content FAMs. In this study, to investigate the effect of Cu content on the microstructure and properties of sintered FAMs, Fe-0.8C-xCu (x = 5–25 wt%) materials were prepared by powder metallurgy method. The density, microstructure, mechanical performance, friction and wear properties of the samples were analyzed. The results demonstrated a significant change in the relative density, hardness, friction and wear properties of sintered Fe-0.8C-xCu samples with increasing Cu content. Particularly, the Fe-0.8C-15Cu samples exhibited outstanding properties, with a relative density of 77.8%, a hardness of 43 HRB, crushing strength of 380 MPa, an average friction coefficient of 0.21, and a wear rate of 1.36 × 10−8 mm3 N·mm−1. The primary wear mechanisms of the Fe-0.8C-xCu specimens include abrasive wear, adhesion wear, chafing fatigue, pitting, and oxidation. This study aims to provide an experimental and theoretical basis for the development of ferrous antifriction materials suitable for heavy-load conditions.

Evaluation of a Commercial MoS2 Dry Film Lubricant for Space Applications

Molybdenum disulfide coatings, particularly Microseal 200-1, have been extensively used as dry film lubricants for actuating mechanisms in space applications. Although Microseal 200-1 has historically been a popular choice for space missions, recent assessments indicate a need for reexamination. This study evaluates sliding friction in air and dry gaseous nitrogen atmospheres at ambient temperatures with both linear reciprocating and rotary unidirectional tribo-tests. Measurements are performed for Microseal 200-1 applied on substrates and surface treatments commonly used in aerospace components, particularly stainless steel and a titanium alloy. Our findings indicate that the friction of stainless steel balls sliding on Microseal 200-1-coated disks is significantly influenced by the environment as well as the disk substrate material. The average friction coefficient ranges from 0.12 to 0.48 in air and from 0.04 to 0.41 in dry gaseous nitrogen, and the amount of friction is consistently much higher for the Microseal 200-1 on the stainless steel than on the titanium alloy. Microscopy and surface analyses, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence, of the coatings on stainless steel substrates reveals that the coatings are sparse and relatively thin, likely a key factor contributing to their high friction. This insight underscores the substrate dependence of this widely used coating and highlights the importance of detailed tribological testing in accurately assessing the tribological performance of commercial dry film lubricants, a key step towards improving the reliability and effectiveness of actuating mechanisms for space applications.

Synthesis of rice‐granular bimetallic nickel/iron phyllosilicates to simultaneously lubricate and strengthen the epoxy‐based composites

AbstractTo improve the subpar lubricating performance of epoxy resin, this paper presents the preparation of a novel bimetallic phyllosilicate featuring a distinctive rice‐granular morphology, which incorporates nickel and iron metal cations through a facile hydrothermal process. These phyllosilicates were then integrated into the epoxy matrix to form composites. A comprehensive analysis of the target product validates the rationality of the synthesis strategy for the as‐prepared rice‐granular bimetallic nickel/iron phyllosilicate, demonstrating a homogeneous hierarchical structure with numerous tiny nanosheets of nickel/iron phyllosilicate grown in situ on the flat surfaces of the rice‐granular metal–organic frameworks. An adequate addition of nickel/iron phyllosilicates allows for excellent dispersion within the matrix and establishes strongly bonded interfaces, steadily increasing the elastic modulus and hardness. Notably, the average friction coefficients decrease from 0.515 for the pure resin to 0.450 for the composites when the filler content reaches 7%, indicating a significant solid lubrication effect. In contrast, adding just 1% nickel/iron phyllosilicate moderately improves wear resistance, elongation at break, and tensile strength. Furthermore, it was found that as the filler content increased, the weight loss rate was reduced by approximately 43.8%, while the residual char increased by 74.2%, significantly enhancing the thermal stability of epoxy composites at high temperatures. This study offers a promising approach to preparing self‐lubricated epoxy composites with favorable mechanical and thermal properties.Highlights NiFePS was successfully synthesized via a facile two‐step self‐polymerization. Excellent mechanical properties of composites could be achieved with low content of NiFePS. The friction coefficient and wear rate were lowered remarkably. The friction mechanism was solid lubrication.

Impact of deposition pressure on the structural, nanomechanical, and tribological properties of δ-TaN coatings deposited via magnetron sputtering on Ti6Al7Nb alloy

In the present study, δ-TaN thin films were deposited by reactive magnetron sputtering (physical vapour deposition) on Ti6Al7Nb alloy by varying the deposition pressure (0.8–0.2 Pa). Their crystalline structure, chemical composition, surface roughness, and surface morphology were investigated by using grazing incidence X-ray diffraction, energy dispersive spectroscopy, scanning probe microscope, and field emission scanning electron microscopy (FESEM), respectively. Structural analysis results confirmed the deposition of cubic δ-TaN thin films along the (111) basal plane; moreover, spherical dome-like surface morphology was observed by FESEM. Further, to analyze the nanomechanical properties of the deposited δ-TaN coatings, such as hardness (H) and modulus (E), scratch tests were performed utilizing the nanomechanical system. Moreover, friction and wear properties of the coating and bare sample (substrate) were investigated on nano-tribometer equipment using a rotary ball-on-disk type configuration. The stainless steel (SS-316) and silicon nitride (Si3N4) balls were used as the counter materials for the tribological tests. The observations of nanomechanical tests revealed that H (GPa), E (GPa), and H/E ratio values increased from 11.83 to 28.30 GPa, 176.02 to 248.45 GPa, and 0.06 to 0.11, respectively, with the decrease of the deposition pressure. In the scratch test, the highest critical load (cohesion failure) was found for δ-TaN coating deposited at the lowest deposition pressure (0.2 Pa). Tribological results of δ-TaN coatings demonstrated average coefficient of friction (COF) value ranges between 0.066–0.092 and 0.072–0.029 against steel and Si3N4 balls, respectively. The wear rate values were observed to vary from 8.15 × 10−5 to 7.56 × 10−6 and from 1.77 × 10−3 to 8.99 × 10−6 against steel and Si3N4 balls, respectively. Generally, the average COF and wear rate decreased against 316 SS and Si3N4 balls as the deposition pressure of coatings decreased. However, the coating deposited at 0.8 and 0.6 Pa against Si3N4 ball showed early delamination of the coating, resulting in the sudden fluctuation in COF plots and higher wear rate in the range of 10−3 mm3/N.m.

The Microstructure and Properties of Ni60/60% WC Wear-Resistant Coatings Prepared by Laser-Directed Energy Deposition.

Ni60/60% WC composite coatings with a good surface roughness and high mechanical properties were successfully prepared on 316L stainless steel substrate by laser-directed energy deposition (LDED) technology. The effects of laser power on the microstructural evolution and mechanical properties of the Ni60/60% WC composite coating were investigated. The relationships between the chemical composition, the microstructure, the hardness, and the friction wear resistance of the composite coatings were characterized and investigated. The results show that the laser power had a significant effect on the energy input, which determined the melting extent of the Ni60 phases around the WC particles and the bonding strength between the reinforcements and the matrix, as well as the bonding strength between the substrate and the coatings. With an increase in the laser power from 800 W to 1400 W, the average hardness of the coating surface increased due to the increased densification of the deposited coatings and then decreased due to grain coarsening under a high energy input. The average coefficient of friction of the coatings decreased gradually to 0.383 at 1000 W, showing a minimum wear of 0.00013 mm2 at 1200 W. The main wear mechanisms on the coated surfaces were adhesive wear and abrasive wear. Moreover, the coatings deposited at 1200 W exhibited better forming quality and wear resistance. This work suggests that the processing parameters during LDED can be optimized to prepare Ni60/60% WC wear-resistant coatings with excellent mechanical properties.

Wear Characteristics of Textured Floating Oil Seal Surfaces: A Simulation and Experimental Study

This study aimed to analyze the effects of surface texture on the wear amount of floating oil seals and how these effects are related to the texture parameters. To achieve this, a finite element model was constructed to simulate the frictional behavior of seal discs under both textured and non-textured conditions. The study focused on a specific set of texture parameters. The texture depth was held constant, while the area density and diameter of the textures were varied. Three different area densities were considered: 10%, 20%, and 30%. Similarly, three different texture diameters were included in the study: 100, 200, and 300 μm. For each combination of area density and diameter, three different texture depths were evaluated: 50, 100, and 150 μm. The results show that compared with the non-texture, the wear loss of the texture is significantly reduced, and the wear loss is reduced by 56.8%. As the texture depth increases, the corresponding increase in wear remains relatively small. In contrast, increasing the texture diameter and area density leads to a more significant increase in wear, indicating that these two parameters have a more significant effect on the wear behavior of the seal. Under the condition of dry friction, the average friction coefficient analysis shows that the texture area density is 30%, the texture diameter is 200 μm, and the minimum value is about 0.602. Under the lubrication condition, the lowest average friction coefficient is about 0.147, the texture area density is 20%, and the texture diameter is 300 μm.

Preparation and tribological properties of PAI/PTFE@Mg-Al LDH polymer-based solid self-lubricating materials

PAI/PTFE composites with 1 %, 2 %, 3 %, 4 % and 5 % of Magnesium aluminum hydrotalcite (Mg-Al LDH) particles were prepared by DC electric field-assisted hot-pressing sintering. The friction and wear properties of the composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), water contact angle and UMT-5 friction and wear tests. The effect of the amount of Mg-Al LDH particles added on the physical properties and friction and wear properties of the composites were analyzed. Experimental results showed that the friction and wear properties of PAI/PTFE composite films can be improved by adding appropriate Mg-Al LDH particles. Among them, The PAI/PTFE polymer based solid lubrication containing 3 % Mg-Al LDH has the best friction coefficient and wear amount, the average friction coefficient is 0.0962 and the wear extent is 1.47×10−5 g. The improved tribological properties of the composite films are mainly due to the excellent mechanical properties of Mg-Al LDH and the good lubrication properties of PTFE.

Promoting densification and strengthening effect of ultrasonic impact treatment on Haynes 230 alloy manufactured by laser powder bed fusion

Laser powder bed fusion (LPBF) has been extensively investigated owing to its high geometry formation accuracy and excellent mechanical properties. However, the LPBFed Haynes 230 parts typically display poor tensile and wear properties due to internal porosity. In this work, the ultrasonic impact treatment (UIT) was applied as a post-treatment to the LPBFed Haynes 230 alloy, porosity and microstructure modulation were performed to improve the strength properties and wear resistance. The pore closure and microstructure were studied by numerical simulations and experiments, and the mechanisms of increasing densification and strength were discussed. Results show that UIT can effectively close pores and reduce porosity, the internal porosity of the ultrasonic impacted layer for one, two, and three times decreases by 63.6 %, 70.9 %, and 81.8 %, respectively. Pore closure is attributed to the residual compressive stress and shear stress introduced by UIT. Besides, the UIT weakened texture strength and refined grains, especially promoting the formation of fine grains. Meanwhile, it also promotes the formation of a high dislocation density and improves the phase structure distribution. Furthermore, the ultimate tensile and yield strengths of the optimal impact process increased by 9.6 % and 34.6 %, respectively. The improvement in strength was attributed to dislocation, grain boundary, and promoting densification strengthening. The average friction coefficient reduces by 4.9 %–14.6 % by refining the surface grains and increasing dislocation density. This work has verified the feasibility of improving the mechanical properties and pore closure of the LPBFed Haynes 230 alloy by UIT.

High-temperature tribological properties of NiCr-Cr3C2 cermet coatings in fluoride molten salts

In this work, the NiCr-Cr3C2 coatings with different Cr3C2 contents were prepared via high-speed laser cladding. The relationships between the composition, microstructure, and high-temperature tribological properties in fluoride molten salts were systematically studied. The results suggest that with the increase of Cr3C2 content, the friction coefficient tends to decrease and stabilize, while the wear rate initially decreases and then increases. Especially for the coating with 60 wt% Cr3C2, it exhibits a favorable tribological performance mainly due to the enhanced hardness imparted by Cr3C2, with an average friction coefficient of 0.12 and a wear rate of 2.78 × 10−6 mm3/Nm. However, the coating experiences delamination damage at 70 wt% Cr3C2 content, leading to an increase in wear rate.

Influence of structure parameters on the tribological properties of MoB/Cu laminated composites

Strong-bonding MoB/Cu laminated (MCL) composites are fabricated by the hot-press method at 1030 °C for 1 h under 20 MPa pressure. The microstructure, tribological properties, and elemental microanalysis are systematically investigated. The structure parameters of laminated composites play a key role in the properties of friction and wear resistance. The average friction coefficient is below 0.3 and the wear rate is almost one order of magnitude lower when the measured ratio of copper thickness to MoB thickness is below 4, compared with the sample whose λ equals 13. The primary phases of MCL are Al2O3, Cu(Al), and MoB. They helped the lubricating film to form on the worn surface during the wear process. These tribo-films effectively moderate the wear while safeguarding the metal matrix.

Convection heat and mass transfer of non-Newtonian fluids in porous media with Soret and Dufour effects using a two-sided space fractional derivative model

Non-Newtonian fluids within heterogeneous porous media may give rise to complex spatial energy and mass distributions owing to non-local mechanisms, the modeling of which remains unclear. This study investigates the natural convection heat and mass transfer of non-Newtonian fluids in porous media, considering the Soret and Dufour effects. A strongly coupled model is developed to quantify the coupled transport of energy and reactive pollutants with the non-Newtonian fluid. The constitutive equation for the non-Newtonian fluid is described by a two-sided Caputo type space fractional velocity gradient. The governing equation, with a symmetric diffusion term, is effectively solved using a stable and convergent shifted Grünwald–Letnikov formula. The influences of three important parameters, which are the average skin friction coefficient, the average Nusselt number, and the Sherwood number, on fluid heat and mass transfer are calculated and analyzed. Numerical results reveal a significant interaction between the fractional derivative and the buoyancy ratio number, both of which affect the average skin friction coefficient. Furthermore, the average Nusselt number increases with the Dufour number while decreasing with the average Sherwood number. These findings enhance our understandings of the dynamics of energy and mass co-transport in non-Newtonian fluids, particularly in relation to their constitutive equation featuring spatial non-local properties.

Improved wear and corrosion protection of Ni–P alloy coating by an electrodeposited Ni–Co–P alloy coating

To improve the comprehensive protection performances of steel C1045 surface, the Ni–Co–P alloy coatings with varying CoSO4·7 H2O concentration (0, 10, 20, 30, 40, 50, 60 and 70 g·L–1) were successfully prepared by an electrodeposition technique on a steel C1045 surface. The effect of the addition of CoSO4·7 H2O in the plating solution on the surface microstructure, elemental composition, crystallite size, microhardness, wear and corrosion resistance of the Ni–Co–P alloy coatings were analyzed by using a scanning electron microscope, an energy dispersive spectroscopy, an X-ray diffraction, a microhardness tester, a friction wear tester and an electrochemical workstation, respectively. The results indicated that the Ni–Co–P alloy coating exhibited a flatter morphology, compact microstructure and more excellent properties compared with Ni–P alloy coating, and the addition and variation of CoSO4·7 H2O in the plating solution had significant effects on the surface microstructure and comprehensive protection performances Ni–Co–P alloy coating. Notably, when the mass concentration of CoSO4·7 H2O in the plating solution was 50 g·L–1, the Ni–Co–P alloy coating had the highest content of Co element (22.67 wt·%), smallest crystallite size (20.41 nm) and highest microhardness (716.2 HV0.1). Furthermore, its wear resistance and corrosion resistance were considerably improved compared to that of the Ni–P alloy coating. The minimum average dynamic friction coefficient, wear scar width and depth of Ni–Co–P alloy coating at 50 g·L–1 were 0.47±0.02, 450.9 µm and 14.1 µm, respectively. The corrosion current density (Icorr) of Ni–Co–P alloy coating was the smallest (0.68 µA·cm–2), the corrosion rate (Rcorr) was slowest (8.25 µm·year–1), and the polarization resistance (Rp) of the Ni–Co–P alloy coating was highest (29.83 kΩ·cm2). The corrosion resistance of Ni–Co–P alloy coating was best.