•Plasma molybdenizing increases FW resistance of Ti6Al4V, but reduces its FF life.•Shot-peened plasmamolybdenizing surface enhances FW and FF resistance of Ti6Al4V.•Combined treatment yields low ...surface-roughness & high hardness gradient distribution.•Combined treatment yields beneficial residual compressive stress & good toughness.•Anti-wear & -fatigue performance improvements for surface engineering applications.
Effect of plasma molybdenizing and shot-peening on fretting wear and fretting fatigue behaviors of Ti6Al4V alloy was investigated. The plasma molybdenized layer composed of a dense molybdenum deposition layer and a Mo–Ti solid–solution layer can increase surface hardness by 2.8 times and cause its volume loss by fretting wear to decrease to 1/14 compared with that of the substrate. Plasma molybdenized treatment results in a significant decrease in resistance of the substrate to fretting fatigue. It is ascribed that the molybdenized layer with high hardness yields a low toughness, and its high surface roughness leads to a micro-notched effect. However, proper combination plasma molybdenizing and subsequent shot-peening may enhance the simultaneous fretting fatigue and fretting wear resistance of Ti6Al4V significantly, which can decrease the fretting wear volume loss to 1/27, and may increase the fretting fatigue life by more than 69 times. A synergistic improvement in fretting fatigue of the titanium alloy by combining surface alloying with shot-peening can be achieved. The results indicate that a beneficial residual compressive stress distribution, high surface hardness with suitable hardness gradient distribution, good apparent toughness, relatively low surface roughness, and excellent surface integrity are achieved.
This article presents an experimental investigation on the fretting wear behavior of piezoceramics P51, PSnN5, and PLiS51 against an Si
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N
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ceramic ball under air condition. A sphere-on-flat ...contact pattern is used as the contact model. The influence of displacement amplitude, frequency, and normal force is taken into account. After each test, friction logs are used to determine the contact interface state. A 3D topography measurement instrument is applied to measure the surface morphology and wear volume. Fretting wear on piezoelectric ceramics under different normal loads, frequencies, and displacement amplitudes are summarized through the collection and analysis of experimental data. It is found that, among the three piezoceramics, PLiS51 has the best wear resistance at higher displacement amplitude and frequency and P51 has the best wear resistance at greater normal force.
•A novel high temperature fretting fatigue test apparatus has been developed.•Surface peeling, delamination and micro cracks occur due to fretting fatigue.•Fretting fatigue cracks initiate on the ...contact leading edge and grow along slip plane.•Fretting fatigue damage mechanism considering fretting wear and crystallographic was proposed.
A novel high temperature fretting fatigue test apparatus was developed to investigate the fretting fatigue mechanism of Nickel-based single crystal (NBSX) superalloys at elevated temperature. The fretting fatigue tests were carried out under 5 loading conditions at 600°C. Results showed that the fretting fatigue life decreased with the increase of axial load and normal load. Metallographic observations revealed that surface peeling, delamination occur at the contact area. Energy dispersive spectrum (EDS) analysis showed that the surface material was oxidized, and the oxides will be compacted onto the contact surface and form a glazed layer. Besides, many micro cracks are observed at the contact surface that are nearly perpendicular to the fretting direction. These micro cracks would either be eliminated due to the large relative displacement or grow into the main crack, which are supposed to be the dominant source of fretting fatigue failure. Multiple fretting fatigue cracks initiate at the contact leading edge area and grow along the (100) plane that is nearly perpendicular to the fretting direction. Then the crack propagation direction will deflect from (100) plane to a series of {111} planes and the specimen eventually failed. The combined effect of fretting wear and crystallographic slip is the cause of fretting fatigue failure.
Schematic of a novel high temperature fretting fatigue test apparatus and fretting fatigue damage mechanism of Nickel-based single crystal (NBSX) superalloy. Display omitted
•Shrink-fit fretting fatigue tests with round geometry and bending cyclic loading.•Experimental evidence of the enhancement effect produced by deep rolling.•Crack arrest approach not adequate ...especially for deep rolled closed cracks.•Shallow crack initiation evidence and correlation to the shear stress amplitude.•Prediction with a multiaxial critical plane fatigue model based on shear stress.
The shrink-fit connection undergoes fretting fatigue at the edge of the contact, where both stress concentration and micro-slip take place. A fretting test set-up with a round-shaped specimen is proposed that eliminates lateral edge contact and misalignment, and is also appropriate for deep rolling. Comparative experiments showed a notable strength improvement, induced by deep rolling, along with the beneficial effect of friction reduction due to lubrication. Multiple cracks with clear shallow paths were evident after SEM observation, thus the maximum shear stress amplitude was assumed as a correlating parameter, while the crack arrest was inappropriate especially for deep rolled specimens.
Running condition fretting map has long been recognized as a useful tool for investigating fretting wear. It illustrates the fretting condition for a fretting couple under different displacement ...amplitudes and loads, which is of great significance for the fretting research. However, it requires a large amount of data to draw running condition fretting map for only one fretting couple, therefore, it is urgent to find a simple method to illustrate the fretting condition. In this paper, the cross-linked polytetrafluoroethylene (XPTFE) with excellent mechanical properties was fabricated by electron beam irradiation. Based on the tribological behavior of XPTFE and PTFE under different displacement amplitudes, it was found that the ratio of static friction force to deformation (Fs/Δd) can be further used to analyze the fretting behavior of fretting couple under specific running conditions. In addition, the Fs/Δd value is closely related to the mechanical properties of the fretting couples. This study provides a new solution for exploring the mechanical properties and running conditions for fretting couples.
•The cross-linked PTFE (XPTFE) with branched 3D network structure is fabricated by electron beam irradiation.•The XPTFE obtains a high hardness and low elastic modulus, and displays a higher wear resistance than PTFE.•XPTFE with low ratio of static friction force to deformation Fs/Δd is prone to be in the partial slip regime.•The fretting running status can be inferred by the mechanical properties of tribo-pairs and certain running conditions.
•An improved coupled 3D fretting wear and fatigue numerical procedure is proposed.•Crack initiation locations were predicted accurately.•The contact stiffness is a key factor in replicating the ...contact behavior during wear process.•A novel damage interpolation scheme, coined as CCPM, is proposed.
This work presents a coupled 3D wear and fatigue numerical procedure for fretting problems in ultra-high strength steel wires that combines Archard’s wear equation with the Smith–Watson–Topper parameter to predict crack nucleation. For total life prediction, a mode I crack propagation based on the weight function method was used. To assess fretting fatigue lifetime, several experimental campaigns were run. The numerical results were in good agreement with the fretting fatigue experimental results. Thus, this study provides a 3D numerical methodology to study the combined effects of wear and fatigue in fretting with a case study in ultra-high strength steel wires.
Fretting occurs when two loaded contacting surfaces are exposed to oscillatory relative movement of small amplitude. Depending on conditions such as surface finishing, coefficient of friction, normal ...load and slip amplitude, fretting may reduce the service life of a component by fretting wear. The effect of surface roughness on the fretting wear profile is still uncertain and may be significant. However, most of the finite element (FE) models that are used to predict fretting wear do not take it into consideration. In this paper, we propose a multiscale procedure to study roughness effect on fretting wear using FE models. In order to do that, we treat the problem in two scales: a) micro scale to analyse the effect of roughness on the contact pressure for frictionless conditions, and b) macro scale to estimate the wear profile evolution for a cylinder on plane contact configuration.
•Multiscale procedure to study roughness effect on fretting wear using FE models.•Micro scale model to analyse the effect of roughness on contact pressure.•A cylinder on plane contact configuration.•Roughness has a minor effect in gross sliding condition.
Much research demonstrated that the fretting sliding condition greatly influences fretting damage. Small displacement amplitudes, inducing partial slip, favor cracking, whereas large dissipative ...sliding gross slip amplitudes favor wear. Considering a Ti–6Al–4V/Ti–6Al–4V cylinder/plane contact, this typical evolution was quantified by plotting the evolution of maximum crack length versus displacement amplitude. Under partial slip, the crack nucleated above a critical tangential loading, related to a threshold δCN_PS displacement amplitude. Above the sliding transition (δt), although tangential loading remained high, crack length decreased to zero at the gross slip threshold δCN_GS, due to surface wear extension which reduced contact stress and removed incipient nucleated cracks. This fretting damage evolution was simulated using an FEM code, enabling synergic modeling of wear and crack phenomena. The crack nucleation risk was quantified using an SWT parameter combined with a linear cumulative damage law. Surface wear evolution was simulated by a local friction energy density wear approach. The three displacement values, δt, δCN_PS and δCN_GS, were shown to be accurately predicted if, respectively, the FEM simulation takes account of the tangential accommodation of the test system, the damage law is calibrated using reverse analysis of experimental partial slip crack nucleation results, and the energy wear rate is determined from the wear volume analysis in gross slip regions next to the sliding transition. This very good correlation enabled “Material Response Fretting Map” modeling and optimization of palliative coating strategy.
•Ti–6Al–4V cylinder/plane fretting damage investigation versus displacement.•FEM Fretting Map modeling combining surface wear and crack nucleation simulations.•Good prediction of partial slip and gross slip Ti–6Al–4V crack nucleation boundaries.•Gross slip cracking domain is inversely proportional to the gross slip wear rate.
WC-12Co coating can be used to improve the wear resistance of mechanical connectors, but due to the fretting behavior between the contact interfaces during service, the problem of fretting fatigue ...cannot be ignored. Through the fretting fatigue experiment and simulation study of the WC-12Co coating, the fretting fatigue mechanism of the coating was investigated under the premise of considering the competitive or coupling relationship between fretting wear and fretting fatigue. Based on Smith-Watson-Topper (SWT) fatigue damage parameter and Miner-Palmgren (M-P) linear cumulative fatigue damage theory, a prediction model for fretting fatigue crack initiation life of WC-12Co coating was established, and the stress redistribution caused by fretting wear was analyzed by Archard wear theory. The analysis results show that the fretting fatigue cracks of the WC-12Co coating mainly initiate at the edge of the wear pits and gradually extend to the substrate; the increase of external load and friction coefficient will accelerate the fretting fatigue process of WC-12Co coating and reduce its fretting fatigue crack initiation life; the change of fretting fatigue crack initiation life and position of WC-12Co coatings caused by fretting wear depends on the change of contact state between contact interfaces.
•A coupled finite element model of fretting wear and fretting fatigue of the WC-12Co coating was established.•The multiple fretting fatigue cracks mainly originate from the edge of the fretting wear pits on the coating surface.•The effects of fretting wear on the fretting fatigue of WC-12Co coatings are affected by the contact state.•Fretting wear can eliminate the original stress concentration and slow down the fretting fatigue crack initiation.
The effects of grain size and bulk hardness on fretting wear behaviors were investigated by solution annealing and subsequently fretting wear test in Inconel 600 alloys. The results indicated that, ...with increase of solution temperature, the grain size increased while the hardness decreased. The average friction coefficients were the almost same, independent of grain size and hardness; while the wear volume decreased with increase of grain size, but the hardness played little role. The smaller grain was conductive to formation of tribological transformed structure (TTS) layer, and produced shorter delamiantion cracks in the TTS layer than larger one.
•Effects of grain size and bulk hardness on fretting behavior of Inconel 600 alloy were studied.•Smaller grain size and higher bulk hardness produced higher wear resistance.•The grain size had a great effect on fretting wear resistance in the gross slipping regime.•The bulk hardness played little role in fretting wear resistance.•The smaller grain was conductive to formation of TTS layer, and produced shorter cracks.
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