Radial fretting fatigue damage of surface coatings

Radial fretting tests with a 52100 steel ball-on-flat contact have been carried out under different normal loads. TiN, MoS₂ and TiN+MoS₂ coatings on a 1045 steel flat were examined. The normal loads amplitude used were 200, 400 and 800 N at speeds of 12 and 1.2 mm/min. Dynamic analysis in combination with microscopic examinations by SEM and EDX have been performed. It was observed that the vertical stiffness increased with the increase of loading speed and number of cycles. The metallographic examinations showed that little damage was observed for the MoS₂ coating, which exhibited excellent radial fretting fatigue resistance. For the TiN coating, micro-cracks appeared at the lower load while delamination occurred at the higher load. For the TiN+MoS₂ composite coating, the vertical stiffness increased but accompanied by some micro-cracks. As a result of the study, the radial fretting test is proposed as one possible new method to evaluate coating life.     

TiN涂层刀具切削高锰钢的磨损破损研究

研究奥氏体高锰钢切削过程中TiN涂层硬质合金刀具的磨损、破损机制,测量了切削温度并得出后刀面磨损量与 切削时间和切削速度的关系曲线,以及刀具前、后刀面显微磨损、破损形貌和化学变化。结果表明,TiN涂层硬质合金刀 具切削奥氏体高锰钢时耐磨性优于单一硬质合金刀具,且适于低速切削(小于30m/min)。     

Fretting fatigue of zinc coated low carbon steel EN H320 M

The object of the present study was to investigate the influence of zinc coatings on steel sheets during fretting fatigue and fatigue tests. The influence of the fatigue stress range, normal pressure and amplitude of slip, on the fracture life was studied for both coated and uncoated EN H320 M steel. The wear produced by fretting was measured and compared with the fracture life evolution for different values of slip amplitude. The wear scars and the fracture surfaces were examined by scanning electron microscopy to identify the degradation mechanism. Although zinc films do not influence the fatigue life of the tested steel, when fretting is superposed on to a fatigue stress the coating markedly improves the fracture life.     

Fretting fatigue and wear damage of structural components in nuclear power stations—Fitness for service and life management perspective

Fretting fatigue and wear problems have major economical and safety impact on the nuclear industry. This keynote paper provides examples of the fretting problems encountered in nuclear power stations and an overview of the methodologies used to assess their root cause, their potential effect on the integrity of structural components and the future damage projection for risk management. The limitations of existing models that are commonly used to predict fretting wear rate are discussed. A system approach to the fretting wear/fatigue problem allowed us to significantly improve the capability of predicting fretting damage through the recognition of the problem nonlinearity, and the effect of self-induced changes. The application of linear elastic fracture mechanics principles for predicting the fretting wear and fretting fatigue strength is demonstrated. The paper underlines the critical roles of the following two factors. First, the validation of the above mentioned methodologies, through experimental investigation of the long-term fretting wear and fatigue behavior of structural components under realistic operating conditions. Second, the qualification of in -situ measurements of fretting wear damage using nondestructive evaluation NDE and inspection methods.     

Fretting behaviour of W-Si coated steels in vacuum environments

This study was focused on the effects of stroke on the fretting behaviour of sputtered W-Si coatings under room and vacuum environments. Fretting tests were carried out with AISI 52100 steel hemispherical ended pin against W-Si coated AISI M2 steel. The tangential force and the applied strokes were monitored during the tests in order to build up the fretting loops. The surface morphology of the wear scars was analysed by optical and scanning electron microscopy (SEM) in order to identify the wear modes and the fretting mechanisms. The shape of the fretting loops was used to characterise the fretting regimes. The formation of adherent films is determinant on the fretting behaviour and depends on the test environment. Electron probe microanalysis (EPMA) was used to analyse the composition of the adherent material and the role of oxides on the formation of the transferred layers. The influence of the coating on the fretting characteristics was discussed comparing coated and uncoated specimens.     

Mo离子注入提高TC4合金微动磨损抗力的研究

对TC4合金进行了Mo离子注入表面改性处理,利用摩擦磨损试验机进行了点接触微动磨损试验,借助读数显微镜和表面粗糙度仪测量出有关参数,计算出试样的微动磨损体积。结果表明,Mo离子注入使试样表面硬度提高,微动磨损体积明显降低。在微动磨损初期,Mo离子注入具有较好的减摩效果。Mo离子注入带来的表面强化效应是基体合金的微动磨损抗力得以提高的主要原因。     

Fretting behavior of low-friction coatings: contribution to industrial selection

Selecting an appropriate low friction coating for a specific industrial application generally remains a challenging task. In the case of fretting conditions, numerous experiments enable us to define endurance life criteria which permit one to follow the evolution of the observed life time as a function of some testing parameters, especially the applied normal load. Complete understanding of the fretting behavior of each coating was not the goal of this study whereas the establishment and validation of a selection route were. Similar to the classical Wöhler curves, these plots give some decisive clues for a pertinent coating selection. However, like all other simple tools, they may screen specific behaviors. A deeper investigation will therefore be required for the final decision.     

Fretting fatigue of laser shock peened Ti-6Al-4V

The objective of this paper is to examine fretting fatigue of laser shock peened (LSP) titanium to quantify the influence of LSP on fretting fatigue life. Contact conditions such as loads and pad geometry are chosen to generate fretting fatigue stresses similar to those occurring in blade/disk contacts in gas turbine engines. LSP treated specimens attained 5-, 10- and 25-fold increase in lives compared to untreated specimens. Metallography of the contact area and fractographic analysis of worn pads detail the fretting behavior of LSP treated specimens.     

Fretting damage assessment of titanium alloys using orientation imaging microscopy

The formation of fretting damage and cracks depends strongly on the microstructure. Recent advances in orientation imaging microscopy (OIM) make it possible to obtain new assessment measurements of the near-surface layers containing fretting damage. In particular, crystallographic grain orientation, misorientations between grains, accumulation of plastic deformation, and the evolution of microstructure leading to microtexture formation and twinning can be determined using OIM. Insight into the hexagonal close packed (HCP) structured metals and alloys is the focus of this study. The examination of the subsurface layers of Ti–6Al–4 V samples reveals that OIM using electron backscatter diffraction (EBSD) is a useful tool to quantify evolution of strain-induced microstructural changes due to deformation in the near-surface layers both in surface treatment processes and in fretting or sliding conditions. Fretting damage in a commercially pure titanium (CP Ti) and a near α Ti–5Al–2.5Sn is also assessed to further evaluate this new characterization method. This study summarizes what can be gained from OIM and the challenges associated with using the technique to characterize near surface microstructures.     

Fretting behavior of shot peened Ti-6Al-4V under slip controlled mode

Fretting tests of shot peened Ti-6Al-4V were conducted under slip controlled mode using a dual actuator test setup which could apply an independent pad displacement at a given applied bulk stress. Fretting regime was identified based on the hysteresis loop of tangential force versus relative slip range and the evolution of tangential force. Fretting regime changed from partial slip to mixed slip and then to gross slip with increasing relative slip range, and the transition from mixed to gross slip occurred at a relative slip range of ∼50 μm regardless of the applied bulk stress magnitude for both shot peened and unpeened specimens. Fretting fatigue life initially decreased as the relative slip range increased and reached to a minimum value, and then increased with an increase of the relative slip range due to the transition in fretting regime from mixed slip to gross slip. Shot peened specimens had longer fatigue life than unpeened specimens at a given relative slip range, but the minimum fatigue life was at the same value of the relative slip range for both shot peened and unpeened specimens. The relationship between relative slip and fatigue life was also found to be independent of the applied bulk stress level. Further, tangential force was directly related to relative slip and this relationship was independent of other fretting variables.     

Fretting Wear Behavior of Laser Peened Ti-6Al-4V

This work deals with the influence of laser peening on the fretting wear behavior of Ti-6Al-4V. Laser peening was carried out on Ti-6Al-4V. The laser-peened surface was characterized by transmission electron microscopy. Surface roughness, nanoindentation hardness, residual stress, and tensile properties of the material in both laser-peened and unpeened conditions were determined. Fretting wear tests were conducted at different normal loads using a ball-on-flat contact geometry. Laser peening resulted in the formation of nanocrystallites on the surface and near-surface regions, increased hardness, and compressive residual stress. Laser peening did not affect the tensile properties and surface roughness significantly. There was no considerable difference between the values of the tangential force coefficient of laser-peened and unpeened samples. The fretting scar size, wear volume, and wear rate of laser-peened specimens were lower than those of unpeened samples. This may be attributed to an increase in surface hardness due to strain hardening and grain refinement at the surface and near-surface regions, higher compressive residual stress, and higher resistance to plastic deformation of laser-peened samples.     

Tribological Behavior of Patterned PVD TiN Coatings on M2 Steel

A series of lubricated pin-on-disk wear experiments were performed to investigate the tribological behaviors of in-line (IN) and staggered (ST) patterned PVD TiN coatings as well as a fully TiN-coated (FC) coating on M2 steel against ASSAB 17 tool steel mating pins. The influence of applied load on the tribological behavior of the individual types of coating was also investigated. The experimental results showed that the tribological behavior of the two patterns and the FC M2 steel sliding against tool steel was a function of applied load. The wear resistance for any PVD TiN coating pattern was relatively higher at the specific individual loadings of 394, 800, 900 and 1100 N for 4 h under wet lubrication. Wear loss of the two types of patterned discs and pins was lower than that of the full coating counterpart. Wear mechanisms are suggested.     

Fretting damage in thin sheets: Analysis of an experimental configuration

A method for evaluating fretting damage in thin sheets was developed for AISI 301 stainless steel in full hard condition in contact with AISI 52100 steel and cast ANSI A356 aluminum. Samples were subjected to fretting and then were subsequently fatigue tested to determine the impact of the fretting damage on fatigue life. A finite element model of the experimental configuration was used to determine the response for the experimental conditions imposed. The values of Fatemi-Socie critical-plane fatigue damage parameter are shown to correspond to the trends in the observed residual fatigue life for contact with AISI 52100 steel.     

TiN多弧离子镀过渡层的组成及其对涂层结合力的影响

论述了ＴｉＮ多弧离子镀涂层过渡层的组成及其形成机制和影响因素。实验结果及分析表明,ＴｉＮ涂层过渡层由混合及扩散层组成,扩散层包括Ｔｉ原子扩散层及Ｎ原子扩散层;影响扩散层的主要因素是基体材料的成分和沉积温度;具有Ｎ原子扩散层的过渡层将使涂层的结合力明显提高。     

Fretting behavior of a rubber coating: Friction characteristics of rubber debris

This paper presents friction characteristics of a rubber coating undergoing fretting-like, oscillatory motion. Results are presented for rubber coated stainless steel as well as uncoated stainless steel experiencing fretting motion. Friction coefficients are experimentally investigated before and after the rubber coating is fully worn out. The effect of load, velocity and displacement amplitude on the friction coefficients of both uncoated and coated stainless steel is discussed.     

Fretting of CoCrMo and Ti6Al4V alloys in modular prostheses

Implantation of a total hip replacements (THR) is an effective intervention in the management of arthritis. Modularity at the taper junction of THR was introduced in order to improve the ease with which the surgeon could modify the length of the taper section and the overall length of the replacement. Cobalt chromium (Co–28Cr–6Mo) and titanium (Ti–6Al–4V) alloys are the most commonly used materials for the device. This study investigates the fretting behaviour of both CoCr–CoCr and CoCr–Ti couplings and analyses their damage mechanisms. A reciprocating tribometer ball on plate fretting contact was instrumented with in situ electrochemistry to characterise the damage inflicted by tribocorrosion on the two couplings. Fretting displacements amplitudes of 10, 25 and 50?μm at an initial contact pressure of 1?GPa were assessed. The results reveal larger metallic volume loss from the CoCr–CoCr alloy compared to the CoCr–Ti alloy, and the open circuit potential indicates a depassivation of the protective oxide layer at displacement amplitudes >25?μm. In conclusion, the damage mechanisms of CoCr–CoCr and CoCr–Ti fretting contacts were identified to be wear and fatigue dominated mechanisms respectively.     

Friction and Wear Behaviors of TiN Coatings under Dry and Vacuum Conditions

In this study, pure TiN coatings were applied on AISI 52100 steel surfaces with a magnetron sputterer at different direct current (DC) powers and N₂ flows to develop a wear-resistant coating for sliding tribopairs working in atmospheric and vacuum conditions. Wear and friction characteristics of these coatings were investigated with a tribometer under both vacuum and atmospheric conditions. DC power and N₂ flow affected the coating thickness and structure. TiN coatings showed different wear and friction characteristics under ambient and vacuum conditions due to the oxidation level of the surface.     

C离子注入对硬质合金刀具TiN涂层性能的影响

在硬质合金刀具上沉积了PVD—TiN涂层,并采用C离子注入技术对其进行表面改性处理。对涂层截面的微观形貌、显微硬度以及与基体附着力的测试结果表明,C离子注入可使TiN涂层的显微组织细密均匀化,并能明显提高涂层的显微硬度以及与基体的附着力。     

A fuzzy logic predictive model for better surface roughness of Ti–TiN coating on AL7075-T6 alloy for longer fretting fatigue life

In this study, the fretting fatigue resistance of AL7075-T6 alloy is investigated using surface treatment Ti–TiN multilayer coating by physical vapor deposition (PVD) magnetron sputtering technique. A fuzzy logic model was established to forecast the surface roughness of Ti–TiN coating on AL7075-T6 with respect to changes in the input process parameters of DC power, temperature, DC bias voltage, and nitrogen flow rate. The results indicate an agreement between the fuzzy model and experimental results with 95.349% accuracy. The fretting fatigue lives of Ti–TiN-coated specimens with the lowest surface roughness resulting from fuzzy logic were enhanced by 18% at low cyclic fatigue, while at high cyclic fatigue the result was reversed.