Stable Wear Stage Research Articles

The Relationship between Tribo-Magnetization and Wear State during Reciprocating Sliding

In order to investigate the relationship between tribo-magnetization and wear phenomena, a series of sliding-friction tests were carried out using a pin-on-block reciprocator type device, which was specially designed to generate sliding friction and to detect magnetic fields. The tribological behavior was observed by a charge-coupled device (CCD) camera in real time, and the magnetic signal was detected by using a two-axis magnetic sensor. It was found that as the friction continues, both the tangential and the normal components of magnetic field on the material surface increase gradually, and that both the average value of the tangential magnetic field ΔH(x)mean and the peak-to-peak value of the normal magnetic field Vpp at the wear scar clearly reflect changes of the wear state. Furthermore, in order to better understand the tribo-magnetization phenomenon, the changes of surface morphology and wear debris in different wear stages were analyzed. Moreover, an improved magnetic dipole model that considered the distribution of magnetic charges on the worn surface was established. This model can successfully describe the tribo-magnetization phenomenon during the stable wear stage, and should be useful for characterizing frictional wear phenomena in the future.

Surface integrity evolution and wear evolution of the micro-blasted coated tool in high-speed turning of Ti6Al4V

The coated tool is one of the most widely used cutters in the processing of titanium alloy. The wear of the coated tool is influenced by its surface integrity which can be improved by surface treatment, such as micro-blasting. The experiment of high-speed dry turning of titanium alloy Ti6Al4V (TC4) is carried out by the PVD-TiAlN coated carbide tools which are untreated and micro-blasted. For the coated tool, the evolution of the tool surface integrity, including tool surface roughness, tool surface topography, tool surface hardness, and tool surface residual stress, is studied at different wear stages. Moreover, the evolution of tool wear is analyzed at different wear stages. Then, the influence of tool surface integrity on tool wear is investigated. It is suggested that the tool surface integrity and wear resistance of the treated tool is improved. The change of tool wear is consistent with the change of coating surface integrity. That is to say, the better tool surface integrity is, the less tool wear will be. In addition, the main tool wear mechanisms are adhesive wear and oxidative wear. In the end, the stable wear stage of treated tools is prolonged, and the tool life is increased by more than 40%.

Coupling Fractal Model for Fretting Wear on Rough Contact Surfaces

Abstract In this paper, a fretting damage model based on fractal theory is proposed. The Weierstrass–Mandelbrot function of fractal theory is used to represent the rough contact surface, and a corresponding contact parameter analysis method is also established. Based on neural network algorithm, the values of fractal parameters are fitted, and the fitting accuracy has been greatly improved compared with traditional methods. According to the fractal parameters of the actual surface, the fretting wear process of the rough contact surface is analyzed based on theory of adhesive and three-body abrasive wear. A generic program for the analysis of three-dimensional fretting wear problems is also proposed. Compared with material tests, the prediction error of the fretting wear simulation model is 13.4% for wear depth and 16.7% and 3.9% for width and length of wear scar in stable wear stage. The prediction results show that the model can be applied to the prediction of the actual three-dimensional fretting wear model.

Investigation of the Optimum Surface Roughness of AISI 5120 Steel by Using a Running-in Attractor

Abstract To investigate the influence of surface roughnesses on the dynamic characteristics of AISI 5120 steel in sliding friction process, a suite of running-in experiments are performed on a pin-on-disk tribometer. The running-in attractor is used to analyze the high-dimensional features of a friction system under different surface roughnesses. The experimental results show that the roughnesses of different original surfaces evolve to the same value in stable wear stage. The pin-on-disk friction system has a chaotic nature and exists a running-in attractor. The original surface of a disk of Ra = 0.953 μm is the most conducive to shorten the running-in duration, reduce the friction coefficient value, and improve the stability of the friction system. This roughness value is termed as the optimum surface roughness. It is an ideal working surface for the friction pair in the running-in design.

Characterization and performance analysis of 3D reconstruction of oil-lubricated Si3N4–GCr15/GCr15–GCr15 friction and wear surface

The performance of rolling bearings is often reduced due to the additional wear introduced by sliding contact. Therefore, it is very vital to study the evolution of the sliding wear process of the bearing material friction pairs. The tribological performance of the two kinds of material pairs, including GCr15–GCr15/Si3N4–GCr15, was analysed under oil-lubricated conditions with a pin-on-disc rig. The results show that with high initial surface roughness, the friction coefficients of the two pairs decrease as the load and speed increase, while in the stable wear stage, Si3N4–GCr15 friction pairs show better tribological properties than those of GCr15–GCr15 friction pairs. For lacks of information-rich studies and techniques of worn surfaces topography, an in-suit 3D microscope is adopted to obtain the topographies of friction and wear surface during the wear tests. The results prove that 3D topography can clearly characterize the wear process. 3D topography shows identical trend with the surface roughness (Ra, Sa and Sq) and the friction coefficients. Citing mixing parameter Sdr explores its feasibility for characterizing worn surfaces. The results illustrate that there is a close relationship between Sdr and 3D topography, which can reflect the friction transition of a surface from running into severe wear. A low surface roughness indicates a small Sdr.

Performance evaluation of creep feed grinding of γ-TiAl intermetallics with electroplated diamond wheels

This paper evaluates the performance of creep feed grinding γ-TiAl intermetallic (Ti-45Al-2Mn-2Nb) using electroplated diamond wheels. Firstly, a comparative analysis with the grinding results by using electroplated CBN wheels was conducted, mainly involving abrasive wheel wear behavior and maximum material removal rate below surface burn limit. It was found that the diamond wheel would produce much better grinding results including lower wheel wear rate and higher maximum material removal rate. Then the surface integrity obtained at different level of material removal rate was characterized with the utilization of the diamond wheel. The poor ductility of this γ-TiAl intermetallic material was found to have a marginal effect on the surface integrity, as no severe surface defects such as material pullout were generated during the stable wheel wear stage. For the involved operating parameters, a deformation layer was produced with ∼10 μm or more in thickness depending on the material removal rate used. Meanwhile, a work-hardened layer extending to more than 100 μm was produced with a maximum microhardness of above 520 HV0.05 (bulk value 360 HV0.05). The residual stress remained compressive, with a value of above −100 MPa and even up to −500 MPa for an elevated material removal rate. Shearing chip was the main chip type, indicating good wheel sharpness in the grinding process.

The self-lubricating behavior and evolution mechanisms of the surface microporous friction interface of M50-(Sn-Ag-Cu) material

The friction interface structure has an important influence on the friction behavior of self-lubricating materials. In this paper, M50 material covered with surface micropores filled with Sn-Ag-Cu (MM-Salloy) was prepared by laser melt deposition. From 25–450 °C, the friction test results show that MM-Salloy exhibits distinguished tribological properties due to the existence of the microporous friction interface. Analysis indicates that Sn-Ag-Cu in surface micropores can dynamically precipitates to the worn surface of MM-Salloy to achieve a lubricating effect, and the increasing of temperature is beneficial to the dynamic precipitation of Sn-Ag-Cu. The whole friction process can be divided into the initial wear stage, fast wear stage and stable wear stage. At stable wear stage, the friction interface is mainly composed of a lubricant-rich surface lubrication layer and a subsurface load-bearing layer, which greatly improves the material's wear resistance. Especially at 350 °C, the surface lubrication layer and subsurface load-bearing layer are most easily formed.

Microstructure, Tribological Behavior, and Strengthening Mechanisms of the Friction Interface Layer with Nanocrystalline Structure of Ni3Al Matrix Self-lubricating Composites

This work investigated the microstructure, tribological behavior and strengthening mechanisms of friction interface layer with nanocrystalline structure of graphene-reinforced Ni3Al matrix composites (GNMCs) synthesized using laser melting deposition. A dislocation density-based model was selected to analyze the mechanisms of the improvement in the wear resistance of the friction interface layer from initial wear stage to stable wear stage. Results show that GNMCs exhibit excellent antifriction and wear resistance in the stable wear stage due to the formation of friction interface layer with nanocrystalline structure. Grain boundary strengthening is the predominant strengthening mechanism of friction interface layer of GNMCs. Dislocations are blocked at grain boundaries to form complex dislocation barriers, further contributing to the high strength and wear resistance. The dislocation density-based model can be successfully used to predict the mechanical response of the friction interface layer subjected to the grain refinement during sliding friction process.

Experimental Study on Machinability of Zr-Based Bulk Metallic Glass during Micro Milling.

The micro machinability of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (BMG) was investigated by micro milling with coated cemented carbide tools. The corresponding micro milling tests on Al6061 were conducted for comparison. The results showed that the tool was still in stable wear stage after milling 300 mm, and the surface roughness Ra could be maintained around 0.06 μm. The tool experienced only slight chipping and rubbing wear after milling the BMG, while a built-up edge and the coating peeling off occurred severely when milling Al6061. The influence of rotation speed on surface roughness was insignificant, while surface roughness decreased with the reduction of feed rate, and then increased dramatically when the feed rate was below 2 μm/tooth. The surface roughness increased gradually with the axial depth of cut (DOC). Milling force decreased slightly with the increase in rotation speed, while it increased with the increase in axial DOC, and the size effect on milling force occurred when the feed rate decreased below 1 μm/tooth. The results of X-ray diffraction (XRD) showed that all milled surfaces were still dominated by an amorphous structure. This study could pave a solid foundation for structural and functional applications.

Precision loss modeling method of ball screw pair

Abstract A precision loss modeling method of the ball screw pair was proposed by introducing an effective contact coefficient to consider the intermittent contact between the balls and screw grooves and the parameter in the precision loss model was modified by establishing a multiscale contact mechanics model. The multiscale contact mechanics model between two rough curved surfaces was established by considering the elastic, elastic-plastic, and plastic deformations of contacting asperities to compute such contact parameters as the total actual contact area and contact load. A surface contact coefficient was introduced into the multiscale contact mechanics model to modify the contact parameters by taking the rough curved surfaces of balls and screw grooves into account. The microtopographies of rough surfaces of screw grooves and balls were characterized by the fractal geometry theory, and then the characterization of the microtopography of screw groove surfaces and the multiscale contact mechanics model were unified in the precision loss modeling. Then the relative sliding distance was calculated according to the kinematic analysis of the ball screw. Finally, the precision loss model of the ball screw pair was established by the above analysis. To verify the effectiveness of the precision loss model, the wear test was conducted on a dual-drive ball screw feed drive system under different working conditions. The predicted results agree well with the experimental data in the stable wear stage and the predictive accuracy of the model is much higher than that of previous studies. The effects of such parameters as the axial load and the feed rate on the precision loss were discussed. It is shown that the precision loss increases with the axial load and the feed rate.

Investigation on Wear Behavior of Cryogenically Treated Ti-6Al-4V Titanium Alloy under Dry and Wet Conditions.

Titanium alloys are widely used in many fields because of their excellent comprehensive properties. However, its poor friction and wear properties limit its many potential applications. In general, the surface roughness of important parts manufactured by titanium alloy should meet certain requirements. As a low-cost and high-efficiency processing method, barrel finishing has been used for the surface finishing of titanium alloys. The main material removal mechanism of barrel finishing is micro-cutting/grinding, which is similar to the material wear mechanism under some conditions. In addition, titanium alloys are subjected to a low force in common surface finishing processes. Cryogenic treatment is a method that can improve the comprehensive properties of titanium alloys. Therefore, the friction and wear behavior of cryogenically treated Ti-6Al-4V titanium alloy (CT Ti alloy) and non-cryogenically treated Ti-6Al-4V titanium alloy (NT Ti alloy) at a low load and scratch speed was studied comparatively in this paper. The results show that the CT Ti alloy exhibits a lower friction coefficient and wear rate under both dry and wet wear conditions. Under wet conditions, the stabilized friction coefficient is lower than that under dry conditions. The stabilized friction coefficient of CT Ti alloy is 0.18 after reaching a stable wear stage under wet conditions. Under dry wear conditions, the NT Ti alloy mainly showed typical abrasive wear, heavy adhesion wear and oxidation wear characters. The wear mechanisms of CT Ti alloy are mainly abrasive wear, slight adhesion wear and oxidation wear. Under wet wear conditions, the wear mechanism of NT Ti alloy is abrasive wear and slight adhesion wear. After cryogenic treatment, the mechanism for CT Ti alloy is slight abrasive wear.

Effect of fiber orientation on the milling performance of quartz fiber composites in cryogenic cooling

Quartz-reinforced polyimide composite is a kind of material with anisotropic and nonuniform properties. The machinability has high dependence on fiber orientation θ. This paper presents the first comprehensive investigation on the cutting model of composites based on fiber orientation. A series of cryogenic cooling milling experiments were carried out to study the influence of fiber orientation on surface morphology, roughness, milling force, and tool wear. The results show that fiber orientation with acute angle has more advantages than obtuse angle. At the same time, it can provide effective chip breaking for latitude and longitude fibers at θ = 45° acute angle. Besides, when the tool is swept 96°, the milling force will reach the maximum, and the shearing effect of the latitude fiber is achieved maximum near θ = 60°. Similarly, the best surface quality is obtained where pits, crack, and burr defects are effectively restrained. Meanwhile, when the chosen cutting speeds are 50, 100, and 150 m/min, the roughness of 0.86 µm, 0.61 µm, 0.5 µm can be attained with θ = 48°, 55°, and 57°, respectively. Although the tool wear is relatively obvious when θ = 60°, the tool is still in a stable wear stage with better machining effect. Hence, it can be concluded that cryogenic cooling machining has better machinability and cutting effect at fiber orientation θ = 60° with larger milling parameters.

Subsurface Dynamic Deformation and Nano-structural Evolution in 40Cr Steel Under Dry Sliding Wear

Dry sliding tribological properties of normalized 40Cr steel pins against quenched and tempered GCr15 discs were investigated under various sliding distances through disc-on-pin contact configuration. Microstructural feature evolution and strain-hardening behavior of worn subsurface in 40Cr pins were systematically analyzed using scanning electron microscopy and transmission electron microscopy. It is found that based on the variation of wear rate, three stages can be divided throughout the friction process: initial wear, slow wear and stable wear. The corresponding microstructures beneath contact surface are subjected to significant strain-hardening effect and structural rearrangement. Nano-grains of 40–100 nm are produced in the topmost subsurface layer and the nanocrystallization mechanism during friction process is further elucidated. Pronounced vortex structures are generated in the localized subsurface zones due to high strain localization and shear instability. With the prolongation of sliding distances, vortex structures suffer dynamic embrittlement and exfoliation from the wear surface as a result of periodically excessive hardening effect, leading to the high wear rate in stable wear stage.

Numerical and experimental studies on the grinding of cemented carbide with textured monolayer diamond wheels

Textured grinding wheels could provide more excellent grinding performances than conventional grinding wheels, which have been experimentally confirmed. However, for lack of in-depth understandings of the grains-workpiece micro contact and interactions, experimental methods can only obtain the macro grinding performances, and the key issues on textured grinding wheels cannot be experimentally explained. In this paper, the combination method of numerical analysis and experiment is proposed. The experiments are conducted to evaluate the machining performances of grinding wheels from a macro level. Meanwhile, numerical methods are used to analyze the distribution characteristics of undeformed chip thickness in micro cutting process. The effects of material removal rate, texture dimension (TD) and radial dressing of grinding wheels on the distribution characteristics of undeformed chip thickness are revealed. The strong correlations between the macro grinding performances and the distribution characteristics of undeformed chip thickness are proved, and what kind of distribution characteristics are beneficial to good grinding results can be discerned, which provides a theoretical basis for tool optimization. Then, optimization strategy and steps of grinding performances are proposed. A conventional grinding wheel with same geometric parameters and grain size is used as reference grinding wheel, and the distribution of undeformed chip thickness generated in stable wear stage by the reference grinding wheel is taken as optimization starting point. After optimization, a desired distribution of undeformed chip thickness can be obtained. Finally, grinding experiments are conducted to confirm the optimization effects. In this way, using the distribution characteristics of undeformed chip thickness as a pointer, the deeper understanding of key issues on textured grinding wheel will be reached.

Milling properties of Kevlar 49 fiber composite based on fiber orientation in cryogenic cooling

Aramid fiber–reinforced epoxy resin matrix composite is an anisotropic and heterogeneous material. And the machinability is strongly dependent on the fiber orientation. In this paper, a composite milling model was established based on fiber orientation θ. Meanwhile, a series of cryogenic cooling milling experiments were carried out to research the influence of fiber orientation on surface morphology, surface roughness, milling force, and tool wear. The results show that the acute angle milling has more advantages than the obtuse one. When tool sweeps at about θ = 55°, the maximum milling force can be gotten. And the maximum shearing action can be reached for latitude fiber at θ = 30°, as well as effectively chip broken for latitude and longitude fibers. Similarly, with increased θ, the shearing fracture is weakened with insufficient chip breaking, but none affected for longitude fibers. Besides, it can be predicted that when the cutting speeds are 50, 100, and 150 m/min, as well as fiber orientation 26°, 34°, and 35°, respectively, the processed surface roughness is 0.93 μm, 0.71 μm, and 0.6 μm. At the same time, tool wear is relatively serious with θ = 40° with a stable tool wear stage, and the processing effect is not affected. Furthermore, using the bigger cutting parameters, the better cryogenic cooling milling effect can be obtained at fiber orientation near 30° with less burr defect.

Effects of the content of MoS2 on microstructural evolution and wear behaviors of the laser-clad coatings

New self-lubricating laser-clad coatings were successfully fabricated on the surface of Ti6Al4V to improve its wear resistance. A new lubricating phase (TiS2) with a lamellar structure was in situ synthesized to resolve the easy-decomposition shortcoming of commonly used sulfides (MoS2, WS2 etc.) during cladding and high-temperature service. Effects of the MoS2 content in the cladding materials on the coatings' macrophologies and microstructures were revealed thoroughly. The evolution in their microhardness and wear behaviors was also explored in detail. Their wear mechanisms were especially highlighted. Results showed that the microstructures of the coatings with MoS2 less than 6 wt% were nearly identical, in which Ti2Ni, TiNi, TiB2 and TiC were in situ synthesized. However, a new spherical phase (TiS2) was in situ synthesized and its volume fraction presented the increasing trend with the increase in content of MoS2 from 6 wt% to 10 wt%. Accompanied with the change, the friction coefficient fluctuated more slightly along with the change in sliding time and its average value was also lower in the stable wear stage. Their wear volumes were similar (about 0.6104 mm3 for 0 wt% MoS2, 0.6408 mm3 for 4 wt% MoS2 and 0.5889 mm3 for 6 wt% MoS2). The wear volumes of the coatings with 8 wt% and 10 wt% MoS2 were significantly reduced to 0.3624 mm3 and 0.2686 mm3, respectively. TiS2 with anti-friction and protection roles can be in situ synthesized in the laser-clad when MoS2 involved in the cladding material exceeds the threshold value of 6 wt%, which significantly improves wear resistance of Ti6Al4V.

Characteristics of the Worn Surface of Magnetized Sliding Contact Medium Carbon Steel/Medium Carbon Steel

The characteristics of the worn surface of a pin were studied in the presence of a DC magnetic field. The experiments were conducted on a pin-on-disk tribometer in the ambient atmosphere. The medium carbon steel/medium carbon steel sliding couple was adopted. Compared to the pin formed in the absence of a magnetic field, oxidation becomes visible on the worn surface of the pin during the process of friction with the action of magnetic field. Fe2O3 was detected from the worn surface of a pin in the stable wear stage. The oxidation area of the worn surface of the pin gradually extends with increasing friction time. The wear of the pin decreases with extending of the oxidation area on the worn surface of the pin. The results reveal that the oxide layer formed on a pin worn surface is one of the key antiwear factors in the presence of a magnetic field.

Finite element simulation and experimental test of the wear behavior for self-lubricating spherical plain bearings

In this study, based on the classical Archard adhesion wear theory, a three-dimensional finite element model was established, with the aim of simulating the failure process of self-lubricating spherical plain bearings in the swinging wear condition. The results show that the self-lubricating spherical plain bearings go through two different stages during the wear process, namely, initial wear stage and stable wear stage. Because the large contact points wear out during the initial wear stage, the maximum contact pressure decreases as the test period increases. The relatively larger wear depth region shows elliptical distribution, and the maximum distribution appears in the central contact area. The wear depth reaches 0.974 mm after swinging 25,000 times. PTFE fibers, which possess a good friction performance but poor abrasion resistance, abundantly exist on the friction surfaces of the fabric liner. Consequently, the friction torque during the initial wear stage is slightly smaller than the friction torque during the stable wear stage; however, the wear rate during the initial wear stage is high. The reliability and effectiveness of the finite element model are verified by experiment. The developed finite element model can be used for the analysis of the wear mechanisms of bearings and the prediction of the service life of bearings.

Tribological Behavior of PTFE Composites Filled with PEEK and Nano-Al2O3

ABSTRACT In this study, the tribological properties of polytetrafluoroethylene (PTFE) composites filled with polyetheretherketone (PEEK) and nano-Al2O3 particles were studied using a block-on-ring wear tester. The tribological performance of the composites was affected by the experimental parameters (sliding speed, normal load, and environmental temperature) and the composites achieved a high-speed sliding friction state. The results showed that the PEEK and nano-Al2O3 particles significantly improved the wear resistance of the PTFE composites. In addition, the nano-Al2O3 particles increased the hardness of the composites and enhanced the mechanical properties to enable applications in a wider range of industrial fields. The effects of the sliding speed and normal load on the tribological properties were more significant than that of the environmental temperature. In addition, the entire wear process was divided into three stages (the initial wear stage, severe wear transition stage, and ultralow stable wear stage), according to the evolution of the tribological characteristics (wear rate, morphology of the worn surface and transfer film, and wear debris morphology).

Quantitative Study on Abrasive Belt Wear Based on Geometric Parameters

In this paper, based on micro wear form, an approach that using protrusion height, average tool angle, blunt area ratio and coated density to describe the wear of abrasive belt is put forward. The method for calculating the above parameters are also introduced. In experiments, we use the profilometer to collect the abrasive belt surface data and draw figures of the above parameters under service time, which indicates that using topography parameters can describe the degree of belt wear. According to parameters changing slope, the abrasive belt service time is roughly divided into two stages, initial wear stage and stable wear stage but no abrupt wear stage. Initial worn stage grains suffer more stress, patterns of wear are mainly severe wear and pull-off, while stable wear stage grains bear less stress and pattern of worn is dominated by mild wear. In addition to that, the other parameters changing trend is agreed and synchronous with protrusion height.