Stable Wear Research Articles

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.

Magnesium Matrix Composite with Open-Celled Glassy Carbon Foam Obtained Using the Infiltration Method

In this study, we present a new composite material that was developed using the pressure infiltration method. In this composite, carbon reinforcement in the form of an open-celled rectangular foam (Cof) was applied, and pure magnesium with two commercial magnesium cast alloys (AZ31, RZ5) was used as the matrix. We examined the microstructure (LM, SEM + EDS) of composites as well as the density, porosity, hardness, compressive strength, flexural strength and tribological properties in dry conditions. It was revealed that the chemical composition of the matrix had a significant impact on the macrostructure, microstructure and properties of the composite. The matrix with rare elements (RZ5) induced poor infiltration of Cof and physicochemical degradation of the reinforcement, while pure magnesium ensured good infiltration, a stable friction coefficient and low wear. For the AZ31 alloy, the effects of infiltration were good; however, an increase in the tribological properties was not observed. Compared with the as-cast matrix materials, the presence of carbon foam in both pure Mg and AZ31 alloy induced an increase in compressive strength and stiffness as well as a decrease in flexural strength. Furthermore, SEM examination of the fractured and wear surfaces microstructure showed structural effects’ dependence on the matrix composition.

Effect of high-frequency micro-vibration on microstructure and properties of laser cladding aluminum coatings

Successful fabrication of AlSiTiNi coatings has been achieved by laser cladding assisted by high-frequency micro-vibration. Under the high-frequency micro-vibration, the dendrites in the coating are fractured and fine structure is formed. A typical bimodal structure is found in the coatings. The bimodal structure could improve the comprehensive properties of the coatings. The partially melted particles are found to be embedded in the fully melted structure at the vibration frequency of 551 Hz. The XRD and EDS investigations show that the coatings mainly consist of FeAl and FeNi phase. The composition distribution of the coatings is uniform due to the intensified convection in the molten pool during laser cladding. The micro-hardness of the coatings shows that the highest hardness of the coating reaches 781 HV0.2 and the average hardness is 725.2 HV0.2 when the vibration frequency is 551 Hz. The friction coefficient of the coating increases slightly and the running-in period decreases. In addition, the friction coefficient is stable and the stable wear time is also prolonged. Moreover, the main wear form of the coating is abrasive wear with slight adhesive wear. The tearing layer of the grinding defect and the wear loss of the coatings fabricated under the high-frequency micro-vibration are both decreased.

Influence of temperature on tribological properties of microarc oxidation coating on 7075 aluminium alloy at 25 °C –300 °C

Abstract The high-temperature tribological properties of bare 7075 Al – Zn – Mg – Cu alloy substrate and microarc oxidation (MAO) coating against ZrO2 ceramic ball were evaluated at 25 °C −300 °C. Coefficients of friction were recorded, and wear rates were determined. Surface morphology and wear scars on the ZrO2 ball were observed. Furthermore, wear mechanisms at three different temperatures were discussed. It was found that the MAO coating could maintain a low wear rate and a stable wear performance in an elevated temperature environment. At 300 °C, the wear rate of MAO coating was merely 1/11 of 7075 aluminium alloy substrate. MAO coating suffered mainly adhesive wear at ambient temperature, and both adhesive wear and abrasive wear at elevated temperatures.

Fe–Si–Al Coatings with Stable Wear Resistance Prepared by Laser Cladding Industrial Wastes

Because wear is one of the most common reasons for the failure of metals, the development of a low-cost coating with enhanced wear resistance is of great importance. In the present study, Fe–Si–Al coatings with superior and stable wear resistance were prepared by laser cladding Fe–Si–Al industrial waste onto 1045 carbon steel. The microstructure, as well as the wear mechanism of the Fe–Si–Al coatings, was investigated. The Fe–Si–Al coatings consist of a (Al, Fe, Si) solid solution phase in both columnar grain form and equiaxed grain form. The Fe–Si–Al coatings possess enhanced microhardness of 494 ± 15 HV0.3 and low mass loss of 5 × 10−5 mg·(N·m)−1. The wear resistance is ten times higher than that of the 1045 carbon steel matrix. The wear of the Fe–Si–Al coatings is mainly dominated by abrasive wear and adhesive wear. This work provides important insight into the preparation of low-cost, wear-resistant coatings, as well as stable, superior wear resistance.

Impact of geometrical parameters of micro-textured DLC on tribological properties under dry sliding friction

To achieve a stable and high wear resistive functional surface under dry sliding friction, the present study proposes micro-textured diamond-like carbon coatings fabricated by ionized physical vapor deposition (I-PVD) using metallic masks. To clarify the suitable geometrical design under dry sliding friction, geometrical quantities of textured array patterns are varied by using metallic masks with different circular hole array patterns fabricated by picosecond pulsed laser processing. The effect of texturing on friction and wear properties is evaluated by ball-on-disk type friction tests for the condition of a constant DLC-coverage per unit area. Thereby, textured DLC pattern with diameters of 50 μm, 100 μm, and 150 μm are applied. Within the first 10 000 laps stable and lower coefficient of friction is obtained with the smallest diameters of 50 μm. However, at further rotation of more than 40 000 laps, the wear of the smaller diameters becomes more pronounced due to the increase of stress concentration at the edge of the structure. Based on these findings, geometrical design of micro-textured DLC coating is discussed with regard to the suppression of three-body plowing and the prevention of stress concentration.

Friction and wear behavior of electroless Ni-P-W coating exposed to elevated temperature

The present study evaluates the effect of operating temperature on the tribological behaviour of electroless Ni-P-W coating developed over mild steel. The constituent of the coating is found to be uniformly distributed. The incorporation of tungsten increases the as-deposit hardness (670 HV0.1) of Ni-P coatings besides improving its crystallinity. The friction and wear tests are carried out under elevated temperature (100 to 500 °C) in a pin-on-disc setup. The results reveal that Ni-P-W coating (especially heat treated ones) display a stable friction and wear behaviour even when subjected to elevated working temperature. The as-deposited coating on the other hand shows increased wear resistance particularly when tested at 300 and 500 °C which is due to microstructural changes induced in the coating because of exposure to high temperature. This is also supported by the excellent hardness shown by the samples after test (46% increase in hardness after testing at 500 °C compared to as-deposited hardness). The applied load and sliding velocity exhibit marginal influence over the friction behavior of the coating especially for heat treated coatings. Study of worn surface reveals that the wear is governed by both abrasive and adhesive mechanisms. Moreover, the formation of oxide layers on the coating at high temperature is also believed to influence the tribological behavior of Ni-P-W coatings.

Sliding wear characteristics of as-deposited and heat-treated electroless Ni-P coatings against AISI E52100 steel ball

In the present experimental study, the wear characteristics of as-deposited and heat-treated, nickel phosphorus (Ni-P) coatings were studied against bearing steel ball (AISI E52100) at ambient dry conditions using linear reciprocating tribometer. The Ni-P coatings were deposited on En24 grade steel using electroless acidic bath and subjected to heat treatment at 400 °C for 1 h under air atmosphere. The phase structure and surface morphology of the coatings were characterized using x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), respectively. Grain size of the coatings was analysed using Scherrer technique. Heat-treated coatings showed 50% improvement in Vickers hardness compared to as-deposited coatings, which is attributed to the formation of Ni3P phase. The stable friction coefficient (∼0.21) and low specific wear rate (4.49E-05 mm3/N-m) were observed for heat-treated coatings in comparison to those of as-deposited coatings. Wear tracks were characterized using SEM and energy dispersive spectroscopy (EDS) in order to understand the wear mechanisms.

Effects of system parameters on the chaotic properties of 52100 steel sliding against 5120 steel

The objective of this study was to systematically investigate the effects of the system parameters on the dynamic properties of the bearing materials during the wear process. The investigated materials were AISI 52100 steel and AISI 5120 steel. The lubricated wear experiments were conducted on a rotating pin-on-disk tribometer at different levels of the normal pressure, velocity, and surface roughness. Two chaotic characteristic parameters, namely the correlation dimension (D) and the average distance between the phase points (da), were used to characterize the wear features using the coefficient of friction (COF). The results showed that the system parameters had strong effects on the running-in time, stable wear time, and value of the COF in the stable state. Additionally, with increasing pressure, velocity, and initial roughness, D initially decreased and then increased and da exhibited similar trends, although the degree of influence was different. The wear properties of the bearing materials were highly sensitive to the system parameters. The results of this study provide insights into the detection and prediction of the wear states of the bearing material, and the improvement of the properties of the bearing material.

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.

Assessment of Wear Form Weights in the Fretting Wear of Spline Couplings with BP Neural Network

This paper investigates the fretting wear behavior of spline couplings under grease and oil lubrication conditions, which includes coupling eccentricity measurement and wear intensity measurement at a tensile test rig. Mechanism analysis of worn splines was also studied to understand the wear forms of the tested splines. Firstly, the wear intensities of spline couplings DIN 5480 45×2×21 8f/9Hlubricated with grease Gleitmo 805 and ISO VG 320 gearbox oil Mobilgear XMP 320 were measured. Test results showed that the wear intensity reduced rapidly in the running-in phase till 3-5×106 load cycles (rotations), depending on the lubrication conditions. After that the spline couplings had a stable wear behavior till 10×106. Secondly the influences of lubrications on splines wear intensities and wear mechanism were studied. It indicated that the spline with grease lubrication had best wear behavior in comparison with oil and not lubricated ones. Finally, a fretting wear intensity calculation method which integrated the weights of adhesive wear, abrasive wear and oxidation wear was developed to calculate the wear intensity of splines.1 BP neural network model was employed for assessment of the weights of each wear form. The BP results showed that mixed adhesive, abrasive and oxidation wear happened in the tested spline couplings, which was verified through chemical composition analysis of the spline teeth faces after different load cycles. The calculated fretting wear agreed well with the tested value, indicating that the developed fretting wear intensity calculation model including wear form weights evaluated via BP neural network simulation had high accuracy on predicting the fretting wear of involuted splines.

Tribological properties of solid lubricants (graphite, MoS2) for Ni based materials

Ni based materials with solid lubrication of 0%, 10% MoS2, 10% graphite, 5% MoS2+5% graphite at weight fractions were fabricated by a P/M hot press method, respectively. The effects of graphite and MoS2 on tribological properties of Ni based materials were investigated on a pin-on-disk tester. Worn surfaces, microstructures of materials were characterized by scanning electron microscopy(SEM). Results indicate that lubrication effects of MoS2 are superior to that of graphite, and the materials with 10% MoS2 has a low and stable wear rates and friction coefficient.

Leakage and wear characteristics of finger seal in hot/cold state for aero-engine

Experimental investigation has been done to approach the leakage and wear characteristics of finger seal in hot/cold state. The High-speed Sealing Test Rig was used in the study. Leakage measurements were done in terms of different working parameters. The pressure ratio changed from 1.1 to 1.8 and the rotating speed varied from 0 to 5000 rpm. The temperature altered from 283 K to 433 K to achieve the cold state and hot state, respectively. Two groups of durability tests were carried out in hot/cold state, separately. Each durability test lasted 300 h with two finger seals. An accurate optical measuring instrument was applied to record the wear growth of the finger seals. Results showed that the flow factor monotonously increases with the pressure ratio and decreases with the rotating speed. An attractive feature is firstly captured that the finger seal with double-laminate achieves lower leakage in cold state while the finger seal with triple-laminate behaves better in hot state. Full life-cycle theory was applied to analyse the wear of the finger seal. The wear growth curve exhibits a rule of SPSP (Sharp Wear, Progressive Wear, Stable Wear and Permanent Wear). Of particular interest is the wear comparison between hot state and cold state, which is firstly discussed in the study and shows that finger seals operating in hot state generate obviously more wear than those in cold state.

Preparation of Polyurethane/Graphite Composite Films with Stable Mechanical Property and Wear Resistance Underwater.

The wear resistance and stable mechanical properties affect the service life of the underwater functional materials to a certain extent. Unfortunately, the current study of underwater functional materials is rarely related to these aspects. Herein, we successfully designed and prepared polyurethane/graphite nanosheet (PU/GN) composite materials, which exhibited excellent wear resistance and stable mechanical properties underwater. The PU/GN composite films were prepared by evaporating a mixed solution of PU and GN on concave hexagonal honeycomb silicon templates. The mechanical properties of the composite films were determined by tensile test, and the wear resistance was evaluated by comparing the surface morphology before and after grind. By adjusting the content of graphite in the composite films, we found that the composite films containing 23 wt% GN had higher tensile strength and superior wear resistance. Moreover, this composite film showed an outstanding stability when expose to water. The impressive results along with simple preparation process made PU/GN composite films had potential applications in robust underwater functional materials.

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.

Stability of Metal Matrix Composite Pads During High-Speed Braking

Metal matrix composites are now commonly used as braking pads for the train running over 250 km/h by virtue of a number of desirable properties. To develop a fundamental understanding of the stability of metallic composites at high-speed braking, four typical composite materials, with different Cu and Fe contents, were subjected to a series of high-speed emergency braking at a simulative running speed of 380 km/h and a braking inertia of 27 kg/m−2 and a normal pressure of 1.27 MPa in this paper. The results showed that the sample with higher Cu content displayed a fade COF and deteriorated wear, but the one with higher Fe content could maintain a stable COF and low wear rate. The tribological behaviour is associated with the relative rate of generation and consumption of the tribo-oxide film. For the sample with higher Cu content, the generation rate of tribo-oxide film was less than the consumption rate, and the COF fading and wear deterioration with the increasing braking times were attributed to the reduction in resistance to deform or to shear the asperities, which was thought to be caused by the degradation of near-surface layer due to the removal of protective tribo-oxide film. In contrast, for the sample with higher Fe content, the generation rate was approximately equal to the consumption rate, and a well-established tribo-oxide film on the surface was responsible for the stable friction level and low wear rates.

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).

In-situ fabrication of novel (Ti, Cr)-N/aluminide multilayer coatings by plasma nitriding Ti-Cr coated Al alloy

In this research, a two-step treatment via depositing Ti-Cr film followed by plasma nitriding was adopted to enhance the surface mechanical properties of 2024 Al alloys. The Al alloys coated with different Ti-Cr films (Cr content, 10%, 25% and 40%) were plasma nitrided at 460 °C for 8 h, in a gas mixture of 40% N2+60% H2. Results showed that the surface coatings consisted of the outer nitride layer including (Ti,Cr)N or (Ti, Cr)N0.3 and the inner Al-Ti-Cr based aluminide layer. With increasing the Cr content, high N content phase (Ti,Cr)N increased in the nitride layer and the thickness of the aluminide layer also increased. The surface hardness of nitrided samples were enhanced by increasing the Cr content, reaching the maximum value of ~1040 HV for the nitride sample with 40 at% Cr. The coefficients of friction for samples with different nitride coatings showed little difference at the stable wear process, with the value of ~0.40. The nitrided samples undergo severe adhesive wear at the initial stage and abrasive wear at the stable stage, accompanied with oxidation wear.

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.