Torsional Fretting Wear Behavior of Bonded MoS2 Solid Lubricant Coatings

The effects of applying a bonded MoS₂ solid lubricant to a 1050 steel substrate were investigated using a torsional fretting wear apparatus. Tests were conducted under a normal load of 50 N with angular displacement amplitudes ranging from 0.1 to 5°. Wear scars were examined using scanning electron microscopy, energy-dispersive X-ray spectrometry, optical microscopy, and surface profilometry. The MoS₂ coating exhibited different torsional fretting regimes than those of the substrate. Fretting regimes of the coating were primarily in the partial slip regime (PSR) and the slip regime (SR) with no mixed fretting regime. The width of the PSR narrowed. Due to the lubricating effects of the coating, the friction torque was consistently lower than that of the substrate. The damage to the coating in the PSR was very slight, and its granular structure remained even after 1,000 cycles. The damage mechanism to the SR coating was a combination of abrasive wear, oxidative wear, and delamination. The MoS₂ coating had potential to alleviate torsional fretting wear.     

Antiwear Properties of Bonded MoS2 Solid Lubricant Coating under Dual-Rotary Fretting Conditions

Bonded MoS₂ solid lubricant coatings are widely used in tribology for their friction-reducing and antiwear properties. However, such coatings have been rarely investigated in complex fretting conditions, such as dual-rotary fretting (DRF). DRF is a complex fretting wear mode that combines torsional fretting with rotational fretting. In this work, the antiwear properties of bonded MoS₂ solid lubricant coating under dual-rotary fretting conditions were studied. Results indicated that the MoS₂ coating had better friction-reducing and antiwear properties than the substrate for alleviating DRF wear. The coating can greatly influence the fretting regimes and reduce the coefficient of friction. Furthermore, the service life of the coating was strongly dependent on the competition of the two fretting components and was reduced as the rotational fretting component increased.     

粘结MoS2固体润滑涂层的转动微动磨损特性

采用粘结法在LZ50钢表面制备MoS2固体润滑涂层,研究MoS2涂层及LZ50钢基体在干态不同角位移幅值下的转动微动磨损行为。在分析转动微动动力学特性的同时,结合光学显微镜、扫描电子显微镜、电子能谱仪以及轮廓仪对磨痕形貌进行微观分析。结果表明:涂层和基体的转动微动运行区域仅呈现部分滑移区(Partial slip regime,PSR)和滑移区(Slip regime,SR),未观察到混合区。涂层改变基体的微动运行区域,使得PSR缩小,SR运行区域向小角位移幅值方向移动。由于MoS2涂层的固体润滑作用,涂层的摩擦因数在整个试验过程都明显低于基体。在PSR,涂层损伤轻微;在SR,涂层的转动微动磨损机制主要表现为剥层和摩擦氧化。研究表明粘结MoS2固体润滑涂层具有明显的防护作用,显著降低LZ50钢的转动微动磨损。     

Effect of contact load on fretting fatigue behaviour of steel wires

Abstract

The tension–tension fretting fatigue tests of steel wires were performed on a self-made fretting fatigue test equipment under contact loads ranging from 40 to 70 N and a strain ratio of 0·8. The results showed that when the contact load increased, the fretting regime of steel wires transformed from gross slip regime to mixed fretting regime. The fretting fatigue life in the mixed fretting regime was significantly lower than that in the gross slip regime. The main fretting wear mechanisms in the gross slip regime, where there were serious fretting damage and a lot of wear debris, were abrasive wear and fatigue wear. Microcracks were observed in the fretting scar of the mixed fretting regime, and the main fretting wear mechanisms were adhesive and fatigue wears. The fretting wear scar was the fatigue source region, and the fatigue fracture surface could be divided into three regions.     

Study on rotational fretting wear of 7075 aluminum alloy

Rotational fretting wear tests in a ball-on-flat configuration have been successfully realized on a special rotational fretting rig developed from an ultra-low-speed reciprocating rotational driver. The rotational fretting behavior of 7075 aluminum alloy against 52 100 steel was studied under different angular displacement amplitudes and normal loads. The results showed that both F_t?θ and F_t/F_n curves can be used to characterize the rotational fretting running behavior, which exhibited different curve shapes and variation trends in different fretting running regimes. The rotational fretting behavior of 7075 aluminum alloy was strongly dependent on the angular displacement amplitude, normal load and number of cycles. The wear of 7075 aluminum alloy was characterized by slight attrition in the partial slip regime, while a combination of delamination, abrasive and oxidative wear was found in the slip and mixed fretting regimes. The formation of a central bulge probably due to plastic flow was observed under gross slip condition of the rotational fretting mode.     

Fretting wear behaviors of a railway axle steel

Fretting damage was one of the most important reasons for the failure of the railway axle. Fretting wear (tangential fretting mode) tests of a railway axle steel (LZ50 steel) flats against 52 100 steel balls were carried out under different normal loads and displacement amplitudes on a hydraulic fretting wear rig. Dynamic analyses in combination with microscopic examinations have been performed. The experimental results showed that the fretting regimes of the LZ50 steel were strongly dependent upon the imposed normal loads and displacement amplitudes. The F_t/F_n curves exhibited different variation trends in different fretting running regimes. The fretting scars presented slight damage in partial slip regime. In mixed fretting regime, the trace of the plowing and plastic deformation flow can be observed on the fretting scars. The wear mechanism during this regime was the combination of the abrasive wear, oxidative wear and delamination accompanied with obvious plastic deformation. The detachment of particles and plowing traces were the main phenomena in slip regime. And, thicker debris layer covered the contact zone of the scar. The severe degradation in slip regime presented the main wear mechanisms of abrasive wear, oxidative wear and delamination.     

Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed(HVOF) technique WC-17 Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope(SEM), energy dispersive X-ray spectroscopy(EDX), and X-ray diffractrometry(XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy(OM), and surface topography. The experimental results reveal that the WC-17 Co coating adjusted the boundary between the partial slip regime(PSR) and the slip regime(SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate's coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating's higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17 Co coating in prevention of rotational fretting wear.     

On the mechanisms of various fretting wear modes

According to relative motion directions for a ball-on-flat contact, there are four fundamental fretting wear modes, e.g., tangential, radial, torsional and rotational modes. In this paper, the mechanisms of these four fundamental fretting wear modes, particularly for the later three modes, have been reviewed from results obtained by the authors in combination with results from literature. Some general features have been reported. Differences both in running and degradation behavior have been discussed in detail. Results showed that some similar laws for three fretting regimes (partial slip regime, mixed regime and slip regime), fretting maps (running condition fretting map and material response fretting map), wear and cracking mechanisms obtained from the classic mode (i.e. tangential fretting) were also identified and useful to characterize the other modes. Nevertheless, the occurrence of relative slip for the radial fretting, the formation of mixed regime for the torsional fretting, the evolution of surface morphology for the rotational fretting were quite different compared to that of the classical fretting mode.     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

聚四氟乙烯基粘结固体润滑涂层微动磨损性能研究

在不同位移幅值与载荷条件下研究了酚醛环氧粘结聚四氟乙烯(PTFE)基固体润滑涂层的微动磨损特性，并利用扫描电子显微镜、表面轮廓仪和傅里叶表面红外仪等对涂层磨斑进行分析。结果表明，粘结PTFE基涂层具有良好的抗微动损伤性能，随循环次数的变化只存在部分滑移区和滑移区，部分滑移区的损伤轻微，滑移区的损伤强烈依赖于栽荷，其损伤与PTFE分子链在往复交变载荷作用下的疲劳断裂相关。     

Effect of Cold Rolling on the Fretting Wear Behavior and Mechanism in Inconel 690 Alloy

The influence of cold rolling on the fretting wear behavior and mechanism of Inconel 690 alloy at 320?°C in air was studied. The wear volume and worn surface were obtained and analyzed using laser scanning confocal microscopy, electron back-scattering diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The grinding surface and strain distribution were also studied by electron back-scattering diffraction to analyze the mechanism of fretting damage. The results indicated that with an increase in cold rolling reduction, the microhardness was increased. However, the friction coefficient and wear volume first increased and then decreased. The characteristics of fretting areas changed from a gross slip regime to a partial slip regime. Accordingly, the damage mechanism in the gross slip regime was a combination of oxidative wear, abrasive wear, and delamination, whereas the damage mechanism in the partial slip regime was mainly adhesive wear.     

基于双重扩展自适应卡尔曼滤波的汽车状态和参数估计

准确实时地获取行驶过程中的状态信息是汽车动态控制系统研究的关键,为此提出了一种新的汽车状态估计器。建立了包含不准确模型参数和未知时变统计特性噪声的非线性汽车动力学模型,针对该非线性系统提出一种双重扩展自适应卡尔曼滤波算法（DEAKF）。该算法采用两个卡尔曼滤波器并行运算,状态估计和参数估计互相更新,同时将带遗忘因子的噪声统计估值器嵌入到状态校正过程和参数校正过程之间,以解决系统的噪声时变问题。基于ADAMS的虚拟试验和实车试验结果表明,该算法的状态估计精度高于EKF方法和DEKF方法的状态估计精度,同时具有良好的模型参数校正能力,对汽车动态控制系统中估计器的设计具有理论指导意义。
     

Effect of surface treatment by ceramic conversion on the fretting behavior of NiTi shape memory alloy

Three types of surface-treated NiTi samples, M-1 (700 °C/0.5 h), M-2 (650 °C/1 h) and M-3 (400 °C/50 h), were prepared by ceramic conversion treatment under different conditions. The effect of the surface treatment on the fretting behavior of NiTi alloy was investigated in the Ringer’s solution by using a horizontal servo-hydraulic fretting apparatus. The experimental results indicated that the surface layer of the low temperature (400 °C) treated samples M-3 was dominated by a single TiO₂ layer, while the high temperature (650 and 700 °C) treated samples M-1 and M-2 consisted of surface TiO₂ layer followed by a TiNi₃ layer. These surface layers were found to have a strong effect on the fretting behavior of the NiTi alloy in terms of changes in the shape of the curves of the tangential force (F _t) versus displacement (d), the fretting regimes and the damage mechanisms involved. The stress-induced reorientation of martensite bands in the NiTi alloy could decrease the slope of the F _t–d curve and thus increase the elastic accommodation ability of the NiTi plate against 1Cr13 steel ball pair. However, since the surface-treated layers could suppress the martensite reorientation in the NiTi substrate and thus decrease the elastic accommodation ability of NiTi, the gross slip started at a smaller displacement amplitude for the surface-treated NiTi samples than for the untreated one. The main wear mechanism of the as-received NiTi alloy in slip regime was adhesion and delamination, while the major damage to the high temperature treated NiTi samples M-1 and M-2 was determined as the spallation of surface-treated layers. Due to the high bonding strength of the surface-treated layer with NiTi substrate, the low temperature treated NiTi samples M-3 showed the best fretting wear resistance in all samples tested.     

High temperature fretting wear behavior of WC-25Co coatings prepared by D-gun spraying on Ti-Al-Zr titanium alloy

Detonation gun (D-gun) spraying is one of the most promising spraying techniques for producing wear-resistance coatings. A thick layer (about 0.3 mm thickness) of WC-25Co with high hardness was covered on Ti-Al-Zr titanium alloy by D-gun spraying and the fretting wear behavior of WC-25Co coatings was studied experimentally on a high precision hydraulic fretting wear test rig. An experimental layout was designed to perform fretting wear tests at elevated temperatures from room temperature (25 °C) to 400 °C in ambient air. In the tests, a sphere (Si₃N₄ ceramic ball) was designed to rub against a plane (Ti-Al-Zr titanium alloy with or without WC-25Co coatings). It was found that the fretting running regimes of WC-25Co coatings were obviously different from those of Ti-Al-Zr titanium alloy. The mixed fretting regime disappeared in WC-25Co coatings, and the boundaries in the running condition fretting map (RCFM) showed hardly any change as temperature increased. The worn scars were examined using a laser confocal scanning microscope (LCSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the coefficients of friction (COF) of WC-25Co coatings at elevated temperatures were nearly constant in the partial slip regime and very low in the steady state. The fretting damage of the coatings was very slight. In the slip regime, the WC-25Co coatings exhibited a good wear resistance, and the wear volume of the coatings obviously decreased with increasing tested temperature. The fretting wear mechanisms of WC-25Co coatings were delamination, abrasive wear and oxidation wear at elevated temperature. The oxide debris layer formed at higher temperature was denser and thicker on top of WC-25Co coatings, thus providing more surface protection against fretting wear, which played an important role in the low fretting wear of the coatings.     

粘结石墨固体润滑涂层微动磨损性能研究

在不同位移幅值与载荷下研究了粘结石墨固体润滑涂层的微动磨损特性，并利用扫描电镜和X射线衍射仪分析了涂层微动磨斑。结果表明：粘结石墨涂层具有良好的抗微动损伤性能，随循环次数的变化只存在部分滑移区和滑移区，部分滑移区涂层损伤轻微；滑移区损伤严重，主要表现为裂纹萌生和扩展，最终按剥层机制呈层状剥落。     

Tribological behaviour and wear mechanism of MoS2–Cr coatings sliding against various counterbody

MoS₂–Cr coatings with different Cr contents have been deposited on high speed steel substrates by closed field unbalanced magnetron (CFUBM) sputtering. The tribological properties of the coatings have been tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The coating microstructures, mechanical properties and wear resistance vary according to the Cr metal-content. MoS₂ tribological properties are improved with a Cr metal dopant in the MoS₂ matrix. The optimum Cr content varies with different counterbodies. Showing especially good tribological properties were MoS₂–Cr8% coating sliding against either AISI 1045 steel or AA 6061 aluminum alloy, and MoS₂–Cr5% coating sliding against bronze. Enhanced tribological behavior included low wear depth on coating, low wear width on counterbody, low friction coefficients and long durability.     

Low-Friction MoS x Coatings Resistant to Wear in Ambient Air of Low and High Relative Humidity

The investigation of the tribological performance of MoS₂-based coatings in air of high humidity is critical for the future use of such low-friction and high-wear-resistant coatings in ambient air. Sulfur-deficient MoS _x coatings with a basal plane (x = 1.3) and a random (x = 1.8) crystallographic orientation were produced by planar magnetron sputtering. The coefficient of friction and the wear loss of MoS_x coatings in comparison with TiN and amorphous TiB₂ coatings were investigated in bi-directional sliding fretting tests performed in ambient air of different relative humidity. The wear rate expressed as a volumetric loss per unit of dissipated energy was determined. From these results, the best friction and wear performance was achieved with basal-plane-oriented MoS _x coatings tested at a relative humidity in the range of 10-50%. A coefficent of friction of 0.06-0.08 and a wear rate of 4 × 10³ m³J^-1, at a normal load of 1 N and a fretting frequency of 10 Hz, were recorded for that type of MoS _x coatings.     

Dissipated energy and fretting damage in CoCrAlY-MoS2 coatings

This paper describes fretting wear behaviour of low friction CoCrAlY-MoS₂ coatings on titanium alloy substrates in terms of dissipated energy and friction coefficient. Experimental characterisation was achieved by measuring the friction coefficient vs fretting cycles, or slid distance. Test results were analysed using exponential evolution functions for fretting damage. Dissipated energy was derived, and predicted and measured values compared. Quantitative evaluation of the fretting damage was performed by measuring substrate area emerged. Results show that the friction coefficient evolution rate of CoCrAlY-MoS₂ coating correlates well with the damaged area fraction and the accumulated dissipated energy.     

Reorientation of Randomly Oriented MoSx Coatings During Fretting Wear Tests

The reorientation of as-deposited randomly oriented sulphur-deficient MoS_x coatings during fretting wear tests has been investigated by X-ray diffraction (XRD), Scanning Electron Microscope and Transmission Electron Microscope. The driving force for the reorientation seems to be the plastic deformation induced by the tangential friction force during fretting tests. The evolution from an as-deposited randomly orientation into a basal one occurs above a threshold normal load and fretting frequency. This reorientation results in a lowering of the coefficient of friction as well as in a high resistance to humidity, but unfortunately a high wear rate is noticed. The effect of normal load and fretting frequency on that reorientation process in MoS_x coatings is discussed.