Improvement of the fretting damage resistance of Ti-811 alloy by Cu/Ni multilayer films

The Cu/Ni multilayer films were prepared on the titanium alloy surface by ion-assisted magnetron sputtering deposition (IAD) technique. The Cu/Ni multilayer films could significantly improve the resistance of fretting wear and fretting fatigue (FF) of Ti-811 alloy at room temperature. The FF resistance of the titanium alloy substrate did not increase monotonically with increase in the modulation period thickness of the Cu/Ni multilayer films. The Cu/Ni multilayer films with modulation period thickness of 200 nm had the highest FF resistance among the prepared Cu/Ni multilayer films for its comprehensive properties with high toughness, high strength and good lubricating action.     

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.     

Dual-motion fretting behavior of mandibular cortical bone against pure titanium

Dual-motion fretting tests of flat cortical bone specimens from fresh human mandible against pure titanium (TA2) ball were carried out on a modified test rig with tilt angle of 45°. The imposed maximal loads varied from 100 to 200 N. Dynamic characteristics of dual-motion fretting tests were analyzed in combination with micro-examinations via optical microscopy (OM), laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM) together with energy dispersive X-ray spectrum (EDX). Two types of F-D curves (the trapezoid and elliptic mode) were recorded during the tests. The examination showed that the wear scars of the dual-motion fretting were asymmetric, and the tangential component of dual-motion fretting was in the mixed fretting regime. Under the lower imposed load, only some detachment of particles and scratches without cracking were observed even after 5×10⁴ cycles. The main wear mechanisms of the dual-motion fretting damage were the abrasive and adhesive wear. Under higher imposed loads, the cracks initiated and propagated mainly at the high stress side of contact edges. The wear mechanisms of the dual-motion fretting of cortical bone under higher imposed loads were the combination of the adhesive wear, abrasive wear, cracking and lubrication of the human bone tissue debris. And the lubrication of the debris played an important role during the dual-motion fretting processes.     

电连接器微动磨损的超声识别与性能退化模型

针对振动环境下电连接器易产生微动磨损而接触性能降低这一问题，采用超声检测方法监测微动磨损过程中电连接器接触件间磨屑的特征值，研究了不同振动条件下接触件的磨损程度及接触性能的退化规律。结果表明，振动频率、振动加速度和振动次数对接触面磨屑的堆积和接触电阻的波动都有正向累积效应；电连接器轴向振动时，磨屑累积效应最为明显。接触电阻和磨屑特征值总量在高振频及加速度下呈现极高的相关性。以磨屑特征值构建的麻雀搜索算法优化BP神经网络性能退化模型的平均绝对误差小于5%。     

The fretting wear of mild steel from room temperature to 200°C

This paper investigates in detail the fretting wear behaviour of mild steel from room temperature to 200°C. Contact resistance measurements and the scanning electron microscope have been used to interpret the wear mechanism in relation to the observed progress of different wear scar parameters. The fretting apparatus used was specially constructed for elevated temperature work, the wear area concentrated in the form of an annulus. It is found that in the fretting of mild steel, there is an initial stage of adhesion followed by a conditioning period before adhesion zones undergo deterioration and dispersal to form eventual oxide debris. The different stages in this mechanism are dealt with in detail. It is found that with mild steel the fretting damage decreases with increase of temperature in the range considered and reaches a constant value at 200°C, the transition temperature. The possibility of abrasive wear as an influencing factor in fretting is also examined but microfatigue is found to be by far the more important process during the steady state.     

The influence of current load on fretting of electrical contacts

The fretting corrosion behavior of tin coated brass contacts is studied at various current loads (1, 2 and 3 A). The typical characteristics of the change in contact resistance with fretting cycles are explained. The fretted surface is examined using scanning electron microscope, laser scanning electron microscope and energy dispersive analysis of X-rays to assess the surface morphology, extent of fretting damage, extent of oxidation, surface profile and elemental distribution across the contact zone. The degradation of contacts at high and low values of current is explained with reference to the thermal and electrical phenomena occurring at the contact interface. The results showed that irrespective of the current loads under study, the contact resistance is maintained at 1.0±0.02 Ω where the oxide debris formation and the electrical breakdown of oxide particles competed with each other maintaining the equilibrium. The number of cycles to failure of the contacts is delayed at lower current. The fretting corrosion degradation of tin coated contacts occurs much faster at higher currents as it generates more accumulation of oxide wear debris at the contact zone. The observed surface morphology and the tin profile of the fretted surface are in agreement with the experimental results.     

Conduction degradation by fretting corrosion phenomena for contact samples made of high-copper alloys

The main cause of electrical contact resistance degradation by corrosion is the vibration of contact interfaces. The purpose of this paper is to analyse the change of contact resistance by means of a vibration test for uncoated sphere/plane contact made of new high-copper alloys.The influence of electrical and mechanical properties of materials, and mainly hardness, on contact resistance has been studied in this work. During the fretting test, a contact point was submitted to 16,000 vibration cycles under fretting amplitude of 50 μm and 1 Hz frequency. The sphere part was fixed, while the plane part was submitted to relative motion. At the end of the test, the fretted surfaces and the wear debris were analyzed by scanning electron microscope and energy dispersive X-ray spectroscopy to evaluate damage, oxidation and elemental composition present in the wear surfaces. In addition, the measurement of the wear track profile using a 3D surface scanning system was introduced. Increases in contact resistance and contact temperature were examined during the fretting test.The results showed that the contact resistance for the harder alloy was higher than that obtained for the other materials. In addition, topographic measurements showed that the small wear track corresponds to the harder material.     

Mechanical and tribological properties of nanostructured TiN/TiBN multilayer films

Nanostructured multilayer films of TiN/TiBN with different bilayer thicknesses (Λ) were deposited onto Si(1 0 0) wafers (for mechanical analyses) and AISI M42 tool steels (for tribological measurements) at room temperature by reactive unbalanced magnetron sputtering in an Ar–N₂ gas mixture. The effects of different Λ values on mechanical and tribological properties were studied by atomic force microscope (AFM), scanning electron microscope (SEM), microindentation measurements, Rockwell-C tester, nano- and micro-scratch tester, impact tester, pin-on-disc tribometer, and Fourier-transform infrared spectroscopy (FTIR). It was found that the mechanical and tribological properties of multilayer films (typically 1.4 ± 0.1 μm in thickness) were closely related to Λ (varied from 1.4 to 9.7 nm). For the best multilayer film with Λ = 1.8 nm, a maximum hardness of 29.5 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of L_C1 (37 N), L_C2 (>80 N) and the highest adhesion strength (HF1). Moreover, by the dynamic impact testing this multilayer film could endure impact cycles up to 4 × 10⁵ without adhesive failure. It was also found that the nano-scratch test under single-pass and constant-load conditions showed that the frictional coefficients decreased with Λ and increased with normal load due to the ploughing effect. The enhanced hardness in the multilayer films with small Λ values improved the wear resistance and lowered the frictional coefficients. The frictional coefficients obtained at 5 N were kept at 0.5 and increased from 0.52 to 0.65 when Λ increased from 1.8 to 9.7 nm at 2 N. By FTIR analyses, the multilayer films with Λ = 1.8 and 2.2 nm showed the presence of h-BN which provided a lubricating function resulted in lower frictional coefficients and wear rates. The tribological properties of the TiN/TiBN multilayer films with different Λ values are also explained in terms of mechanical properties and wear mechanisms.     

Fretting wear behavior of AZ91D and AM60B magnesium alloys

The fretting wear behavior of the AZ91D and AM60B magnesium alloys are investigated using a reciprocating fretting wear machine under dry conditions with different numbers of cycles, different normal loads, slip amplitudes and frequencies. The worn surfaces and wear debris were examined using scanning electron microscopy and optical microscopy in order to understand the predominant wear mechanisms of two magnesium alloys. The results indicate that the AZ91D alloy displays a lower friction coefficient and lower wear quantity than the AM60B alloy. The AZ91D shows a higher capability than AM60B in resisting crack nucleation and propagation. Both AZ91D and AM60B show similar friction and wear characteristics. The wear quantity increases with increasing normal load, but decreases with increasing frequency. The friction coefficient also decreases as the normal load is increased. Fretting frequency had little effect on the friction coefficient. In a long term, the fatigue wear and abrasive wear were the predominant wear mechanisms for AM60B and delamination wear, adhesive wear and abrasive wear for AZ91D.     

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component (such as carbon, nitrogen, sulphur and oxygen, etc) thermo-chemical treatment(LTGMTT) can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 (0.48%C) steel prepared by low temperature gas multi-component thermo-chemical treatment (LTGMTT) technology. The fretting wear tests of the modified layer flat specimens and its substrate (LZ50 steel) against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope(SEM), optical microscope(OM), X-ray diffraction(XRD) and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime(MFR) of the LTGMTT modified layer diminished, and the slip regime(SR) of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction(COF) of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime(PSR) was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.     

Lubricating film thickness measurements with bovine serum

Lubricant film thickness measurements were made for bovine serum solutions under steady state rolling and sliding. The effect of low (30 MPa) and high contact pressures (200 MPa) was examined. In the high pressure rolling tests BS initially formed films 5-50 nm thick over the speed range. However, in subsequent speed sweeps, a relatively speed independent film of 40-50 nm developed. In some cases thick (up to 100 nm) films were formed at low speeds; this behaviour was considered representative of high-viscosity surface layers rather than of solid films. At the end of each test residual boundary films of 9-19 nm were measured under static loading. These are attributed to the multilayer adsorption of protein molecules and will provide surface protection during stance or on initiation of gait. The results at low pressure showed that much thicker films (∼60-80 nm) were formed over the same speed range. Again thicker films were formed at the lower speeds. There was significant scatter in the film thickness results, possibly due to the inherent nature of the fluid, which is an inhomogeneous biological solution. The film thickness/speed behaviour was not representative of a simple Newtonian fluid and this has considerable implications for the development of predictive film thickness models and new designs of artificial hip joints.     

Different aspects of the role of wear debris in fretting wear

Two different aspects of the role of oxide wear debris in fretting wear are studied by allowing them to escape from the interface during sliding. This is accomplished by laser surface texturing that forms regular micro-pores topography on the friction surfaces which enables this escape. It is found that the role of oxide wear debris depends on the dominant fretting wear mechanism. Their presence in the interface protects the friction surfaces when the dominant wear mechanism is adhesive and harms the friction surfaces when this mechanism is abrasive. The escape of oxide wear debris into the micro-pores results in up to 84% reduction in the electrical contact resistance of the textured fretting surfaces.     

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.     

Fretting wear of Ti-48Al-2Cr-2Nb

An investigation was conducted to examine the wear behavior of gamma titanium aluminide (Ti-48Al-2Cr-2Nb in atomic percent) in contact with a typical nickel-base superalloy under repeated microscopic vibratory motion in air at temperatures from 296–823 K. The surface damage observed on the interacting surfaces of both Ti-48Al-2Cr-2Nb and superalloy consisted of fracture pits, oxides, metallic debris, scratches, craters, plastic deformation, and cracks. The Ti-48Al-2Cr-2Nb transferred to the superalloy at all fretting conditions and caused scuffing or galling. The increasing rate of oxidation at elevated temperatures led to a drop in Ti-48Al-2Cr-2Nb wear at 473 K. Mild oxidative wear was observed at 473 K. However, fretting wear increased as the temperature was increased from 473–823 K. At 723 and 823 K, oxide disruption generated cracks, loose wear debris, and pits on the Ti-48Al-2Cr-2Nb wear surface. Ti-48Al-2Cr-2Nb wear generally decreased with increasing fretting frequency. Both increasing slip amplitude and increasing load tended to produce more metallic wear debris, causing severe abrasive wear in the contacting metals.     

Fretting wear behavior of nitrogen ion implanted titanium alloys in bovine serum lubrication

Nitrogen ion implantation was performed on biomedical titanium alloys by using of the PBII technology to improve the surface mechanical properties for the application of artificial joints. The titanium nitride phase was characterized with X-ray photoelectron spectroscopy (XPS). The nanohardness of the titanium alloys and implanted samples were measured by using of in-situ nano-mechanical testing system (TriboIndenter). Then, the fretting wear of nitrogen ion implanted titanium alloys was done on the universal multifunctional tester (UMT) with ball-on-flat fretting style in bovine serum lubrication. The fretting wear mechanism was investigated with scanning electron microscopy (SEM) and 3D surface profiler. The XPS analysis results indicate that nitrogen diffuses into the titanium alloy and forms a hard TiN layer on the Ti6Al4V alloys. The nanohardness increases from 6.40 to 7.7 GPa at the normal load of 2 mN, which reveals that nitrogen ion implantation is an effective way to enhance the surface hardness of Ti6Al4V. The coefficients of friction for Ti6Al4V alloy in bovine serum are obviously lower than that in dry friction, but the coefficients of friction for nitrogen ion implanted Ti6Al4V alloy in bovine serum are higher than that in dry friction. Fatigue wear controls the fretting failure mechanism of nitrogen ion implanted Ti6Al4V alloy fretting in bovine serum. The testing results in this paper prove that nitrogen ion implantation can effectively increase the fretting wear resistance for Ti6Al4V alloy in dry friction, and has a considerable improvement for Ti6Al4V alloy in bovine serum lubrication.     

On the behaviour of an oil lubricated fretting contact

Although many engineering situations involving fretting damage are lubricated, comparatively little has been reported on this aspect of fretting wear. The viscosity of the lubricating oil and its boundary layer performance are expected to influence fretting behaviour, in addition to the normal fretting parameters, such as stroke and contact force.

This paper examines the effect of lubrication regime, oil viscosity and stroke on the behaviour of a ball-against-flat specimen arrangement. Ball and flat specimens were both manufactured from a bearing steel (SUJ2). Polybutane oils, without additives, covering a range of viscosities from 1 to 10 000 cSt, and fretting strokes up to 35 μm were investigated. The lubricating oil was added to the fretting interface after 0, 3 and 2000 fretting cycles had been completed. Lubrication regime, oil viscosity and stroke were all found to affect fretting behaviour in terms of both coefficient of friction (or traction coefficient) and wear. For strokes less than 9 μm, i.e. for conditions approaching almost complete ‘stick’, coefficient of friction values under oil lubrication were well in excess of double those observed without it. These high values suggest that the oil was unable to penetrate into the fretting contact region, but did maintain a shield around it, so that metal-on-metal contact was maintained under oxygen deprived conditions. The lowest values of steady state coefficient of friction (≈ 0.2) were observed when oil lubrication was applied after 2000 cycles had been completed, indicating that surface roughening and the presence of oxide films and oxidised debris assisted penetration of the lubricant into the fretting contact zone.     

On the fretting wear mechanism of Zr-alloys

Zirconium alloys are highly desirable in nuclear applications due to their transparency to thermal energy neutrons and for their high corrosion resistance. The main objective of this study is to investigate the fretting wear mechanism of Zr–2.5%Nb alloy. The experimental work was carried out in air at 265 °C, using a specially designed fretting wear tribometer. The transfer of material, the change in the wear volume and the maximum wear depth with the number of cycles were measured through 3D mapping of the topography of the fretted surface. SEM and Fourier Transform Infrared Interferometry methods were used to examine the microspall pits and to measure the distribution of the thickness of oxide layer in the fretting region. For relatively small slip amplitude, the results showed that the fretting wear mechanism is initially dominated by adhesion and abrasion actions and then by delamination and surface fatigue. The time variation of the wear losses was shown to be cyclic until a steady state value is reached. At high slip amplitudes, however, abrasion and delamination are the only dominant wear mechanisms. The volumetric wear losses were found to decrease monotonically with the number of cycles. A novel approach was introduced, whereby the thermal and electrical contact resistances of the fretting interface are simultaneously measured. The results demonstrated the potential use of this non-intrusive approach for real-time monitoring of the fretting wear mechanism.     

An experimental study torsional fretting behaviors of LZ50 steel

Four simple fretting modes are defined according to relative motion: tangential, radial, rotational, and torsional fretting. This paper presents a new test rig that was developed from a low-speed reciprocating rotary system to show torsional fretting wear under ball-on-flat contact. Torsional fretting behavior was investigated for LZ50 steel flats against AISI52100 steel balls under various angular displacement amplitudes and normal loads. The friction torques and dissipation energy were analyzed in detail. Two types of T–θ curves in the shape of quasi-parallelograms and ellipticals were found that correspond to gross and partial slips, respectively. The experimental results showed that the dynamic behavior and damage processes depend strongly on the normal loads, angular displacement amplitudes, and cycles. In this paper, the debris and oxidation behaviors and detachment of particles in partial and gross slip regimes are also discussed. Debris and oxidation are shown to have important roles during the torsional fretting processes. The wear mechanism of torsional fretting was a combination of abrasive and oxidative wear and delamination before third-body bed formation. The mechanism was then transformed into third-body wear after a great amount of debris formed.     

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.     

DLC多层膜对1Cr1 8Ni9Ti钢微动磨损性能的影响

用非平衡磁控溅射与等离子体源离子注入（PSII）的混合技术，研究了类金刚石碳（DLC）多层膜对1Cr18Ni9Ti钢微动磨损性能的影响。结果表明：注入N后，改性层内形成了CrN和Fe3N等氮化物相；PSII技术能够提高1Cr18Ni9Ti钢基体的微动磨损性能；试验所制备的DLC多层膜比N注入层具有更好的微动磨损性能。