Mixed Slip Regime Research Articles

Fretting wear mechanism of DZ125 surface created by WEDM

In this paper, the fretting wear mechanism of the directionally solidified superalloy (DZ125) surface created by wire electrical discharge machining (WEDM) are studied. Samples with varying surface characteristics are prepared by changing the number of wire cutting (NWC), ranging from one to five times (NWC-1 to NWC-5). Comparative analysis reveals that the NWC-3 exhibits the best surface characteristics. Subsequent fretting wear tests under different displacement amplitudes show increased dissipation energy with greater displacement. Compared with other samples, NWC-3 in the synergistic effect of surface roughness and hardness exhibits excellent fretting wear performance. In addition, the fretting mechanism transitions from mixed slip regime (MSR) to gross slip regime (GSR) as the displacement increases. The wear mechanism transitions from abrasive wear to oxidation wear and adhesive wear.

Fretting wear behavior and wear mechanism of selective laser melting IN738LC alloy with various loads and micro-structures

In this study, the ambient temperature fretting wear behavior and the wear mechanisms of the Selective Laser Melting prepared IN738LC alloy with various micro-structures were systematically investigated under varying load conditions (35 N, 100 N). The results indicate that the running states of fretting gradually transitions from the gross slip regime (GSR) to the mixed slip regime (MSR) as the load increases. The HT-2 samples (Unimodal precipitation, hardness 512 HV) present more fine homogeneous and dense secondary γ′ phase compared with HT-1 (Bimodal precipitation, hardness 487 HV) and As-built (No precipitation, hardness 392 HV) counterpart, which result in excellent wear resistance. The main fretting wear mechanisms for all samples were oxidation wear, abrasive wear, fatigue wear.

Effect of fretting wear on TC4 alloy prepared by laser shock peening at high temperature

The fretting wear properties of a nanocrystalline layer with laser shock peening (LSP) on the surface of Ti–6Al–4V (TC4) alloy were investigated to improve the fretting friction performance at 25 °C and 500 °C. The fretting operation characteristics and material damage mechanism of the LSP–TC4 alloy were investigated through a friction dissipation model and two kinds of operation fretting models. The contact morphology and three-body behaviour on the surface were also revealed. The wear resistance performances of the strengthened surfaces exceeded those of unreinforced surfaces at 25 °C and 500 °C but the LSP-treated alloy was more stable at 25 °C. As revealed in the operation fretting models, the fretting running region of the LSP layer consisted of a mixed slip regime and gross slip regime. The material response area was composed of slight and abrasive wear areas at 500 °C. The improved fretting fatigue resistance of TC4 alloy was attributed to the refined internal organisation and high-density dislocation organisation of LSP, which inhibits the initiation and propagation of fatigue cracks.

Understanding the microstructural evolution and fretting wear behaviors of M50 bearing steel heat treated at different temperatures

For M50 bearing steel, which is widely used in aerospace engine main bearings, fretting wear is an important but neglected category of wear failure during engine cold startup. High temperature tempering is crucial in heat treatment to enhance its microstructure and wear resistance. In order to investigate the influence of different tempering conditions on fretting wear performance of M50 steel, it is essential to conduct a comprehensive study. This research explores how heat treatment processes affect the fretting wear properties of M50 steel by varying the tempering temperature (450 °C, 500 °C, 550 °C, 600 °C, and 650 °C). We analyzed the microstructure evolution and fretting wear behavior under different conditions using SEM, EDS, XRD and other characterization methods. The results show that the tempering temperature influences fretting wear through martensite, retained austenite, and carbide transformations. In the 450 °C–600 °C range, wear volume and wear rate decrease with hardness. At 550 °C tempering, M50 achieves the highest hardness (59.71 HRC) and a lower wear rate (9.661 × 10−8 mm3/(N·mm)). M50 steel exhibits optimal fretting wear performance at 550 °C tempering. Overall, wear behavior occurs in the mixed slip regime, shifting towards partial slip with higher tempering temperatures. When the tempering temperature is low, the fretting wear mechanism is predominantly dominated by fatigue wear and abrasive wear, while at higher tempering temperatures, the fretting wear mechanism is primarily governed by oxidative wear and adhesive wear.

Hexagonal boron nitride nanosheets eco-friendly dispersed in pure water for lubrication in fretting contacts between steel pairs

The lubricating effect of h-BN nanosheets, dispersed in pure water without the use of any chemicals, was investigated under fretting contacts. The resistance against oxidation of sliding pairs was also considered using AISI 52100 and AISI 304 steel pairs separately, given that oxidation is inevitable on steel surfaces. In the partial slip regime, effects of the type of lubricant and oxidation on wear and friction were insignificant. In the mixed slip regime, the mending effect of h-BN counteracted the oxidation of sliding surfaces, resulting in mild wear. In the gross slip regime, the mending effect collapsed due to oxide debris, resulting in severe wear. Moreover, the results showed that the presence of h-BN nanosheets influenced the transition of fretting regimes. These findings suggest that aqueous-dispersed h-BN nanosheets can be an effective eco-friendly lubricant additive, particularly when fretting conditions enable a stable mending effect and sliding surfaces exhibit high corrosion resistance.

Study on the damage evolution of fretting wear in an Inconel 718 laser cladding alloy layer at different temperatures

In this study, Inconel 718 alloy samples were prepared by laser cladding deposition technology, and GCr15 steel balls were selected as the friction pair. The tangential fretting wear tests were conducted in ball-on-flat point contact mode using a self-developed multifunctional fretting wear tester. The damage evolution law of fretting damage with the number of cycles for laser cladding Inconel 718 alloy was investigated at room temperature (RT) and 400 °C. The obtained results reveal that the coefficient of friction curves and energy dissipation value in the process of fretting wear first increased, then decreased, and finally reached a stable state with increasing cycles. At room temperature, the fretting running states gradually changed from mixed slip regime (MSR) to gross slip regime (GSR). There was clear spalling in the fretting damage zone, and a large mass of wear debris was formed on the worn surface. As the test time continued, the width and depth of the wear marks gradually increased, the volume of material wear increased, and the wear damage of the material gradually aggravated. When the test temperature was 400 °C, the fretting was running in the MSR. As the number of cycles increased, spalling and adhesion of wear debris occurred in the fretting damage zone. The main mechanisms of fretting wear were oxidation wear, abrasive wear, fatigue wear and adhesive wear.

Research on fretting regime transition of DD6 single- crystal superalloy via femtosecond laser-induced asperity and hardened layer

In this study, the fretting wear test was performed on DD6 single-crystal superalloy after femtosecond laser modification (FLM) to evaluate the influence of femtosecond laser-induced asperity and hardened layer on its fretting regime. Results show that the ablation layer with a depth of ∼ 3.2 μm and the deformed layer are formed beneath the surface, with an increase in surface roughness and hardness. The ablation layer is composed of Al2O3, Cr2O3, and spinel structures. However, the diffraction peak and near-surface orientation after FLM remain similar to those in DD6 single-crystal superalloy substrate, indicating that no remarkable phase change and recrystallization occur despite thermal effect during FLM. The hardened layer has lower plasticity, and the asperities are easy to remove, which results in material removal predominating during the friction process. Therefore, the asperity and hardened layer induced by femtosecond laser could change the fretting regime of DD6 single-crystal superalloy from mixed slip regime (MSR) to gross slip regime (GSR). FLM provides a possibility to replace crack initiation with acceptable material removal in special conditions.

Study on the fretting wear behavior over a wide temperature range of an Inconel 718 superalloy deposited by laser cladding

Fretting tests were performed on an Inconel 718 superalloy against GCr15 steel in a range of 25 ℃ < T < 400 ℃ to investigate the wear mechanism of the laser cladding-deposited Inconel 718 superalloy over a wide temperature range. The results show that when the displacement amplitude was 15 μm, the fretting was running in a partial slip regime (PSR), and the wear damage mainly showed elastic–plastic deformation, fatigue wear and abrasive wear. When the displacement amplitude increased to 100 μm, fretting occurred in a mixed slip regime (MSR) and gross slip regime (GSR). With continuous fretting wear, the dissipated energy of the material decreased gradually with increasing temperature in a stable state. The wear damage was mainly combined with fatigue wear and peeling. When the temperature was 100 ℃, the coefficient of friction (COF) value in the stable state was large. As the temperature increased, adhesive wear and oxidative wear gradually predominated in the fretting tests. The effect of high temperature easily formed an adhesive layer on the worn surface with wear reduction, especially at a high displacement amplitude.

Torsion Wear Behavior of PEEK-on-UHMWPE as an All-Polymer Joint Combination in Total Knee Replacement

Polyether ether ketone (PEEK) has been considered as an alternative material to cobalt chrome in the femoral component of a total knee replacement. In this article, the experimental simulation of torsion wear for a PEEK and CoCr femoral head against an ultra-high-molecular-weight polyethylene (UHMWPE) tibial pad was carried out using a two-station knee simulator. The testing results showed that T-θ curves of torsion wear for PEEK-on-UHMWPE bearing couples showed three types of morphological characteristics, such as linear, elliptical, and parallelogram shapes. With an increase in torsion angular displacement, T-θ curves changed from the linear to the parallelogram type, and the relative motion state changed from the partial slip regime coordinated by the elastic deformation to the slip regime with plastic deformation. With an increase in normal load, the T-θ curve changed from the parallelogram to the elliptical type, and the relative motion state changed from the slip regime to the mixed slip regime. Under intermediate torsion wear conditions, the wear factors of UHMWPE were 11.25 ± 2.08 × 10−6 mm3/C and 14.65 ± 2.49 × 10−6 mm3/C against PEEK and CoCr. Under high torsion wear conditions, the wear factors were 20.51 ± 3.23 × 10−6 mm3/C and 23.26 ± 3.01 × 10−6 mm3/C, respectively. The wear surface of UHMWPE against PEEK showed slight adhesive wear and plastic deformation in the center, and abrasive wear with local fatigue spalling was found at the edges. The wear topographies presented characteristics similar to the CoCr bearing combination.

Study on the fretting maps of Zircaloy-4 alloy against Inconel 718 alloy

Fretting wear tests of Zircaloy-4 alloy against Inconel 718 alloy were conducted on a fretting wear rig. The contact state and fretting running characteristics of Zircaloy-4 alloy were investigated. The running condition fretting map of Zircaloy-4 alloy presents three regimes, namely, partial slip regime, mixed slip regime, and gross slip regime. Slight degradation was observed in the partial slip regime. In the mixed slip regime, adhesive wear of the stick zone and oxidation wear of the slip zone are the main damage mechanisms, and cracking was observed at the stick-slip boundary. Severe material detachment due to wear is predominant in the gross slip regime, and the main damage mechanisms are adhesion, plastic deformation, surface fatigue, frictional oxidation and abrasion.

Ti-6Al-4V fretting wear and a quantitative indicator for fretting regime evaluation

Fretting wear between titanium alloy components in aero engine is prevailing in the blade dovetail, the blade crown, and the damping shoulders. In this study, the fretting wear behavior of Ti-6Al-4V alloy was investigated by changing the load and displacement under a high frequency (100 Hz). To simulate the actual working conditions in aero engines, both the ball and flat samples were Ti-6Al-4V alloy. It was found that as the load increased, or as the applied displacement decreased, the fretting regime changed from gross slip regime to partial slip regime. The coefficient of friction/traction at steady stage decreased as load increased. Wear scar morphologies varied with fretting running conditions. In gross slip regime, the central area was higher than the rest region of the wear scar. In the mixed slip regime, large material accumulation could be found at both ends of the reciprocating motion. In partial slip regime, a nearly original fretting sample surface was observed in the central area and wear occurred in the edge area. Furthermore, considering the wear of the paired samples, a method based on the fretting wear scar diameter was proposed to evaluate the fretting running conditions.

Experimental study on fretting-fatigue of bridge cable wires

Bridge cables are subjected to small relative sliding and high contact stresses among wires under fluctuating loads and repeated bending, eventually leading to fretting-fatigue failure. This paper presents a series of fretting fatigue tests with different fretting and fatigue parameters to investigate the tribological properties, fretting fatigue characteristics and fracture failure mechanism. Results show that the fretting-fatigue failure evolved from surface micro cracks at the trailing edges generated from a mixed slip regime. Larger fretting amplitude induced larger tangential force and coefficient of friction, and decreased life. Fretting scar depth increased as fretting-fatigue proceeded while the growth rate was declining.

Finite element implementation of a varied friction model applied to torsional fretting wear

Coefficient of friction is a significant factor for investigating stress and strain on the contact surface for a problem on torsional fretting wear. First, in this paper, a variable coefficient of friction model related to space and time is introduced. The evolution of friction coefficient is governed by the local contact history and the slip distance. Then, this model is implemented in the finite element code ABAQUS by the user subroutine FRIC. A sphere–plane finite element model is constructed to simulate stress and strain on the contact surface under the torsional fretting loading. Comparisons between the experimental friction torque curves and the numerical data rooting from this model show a good agreement. In view of the relation between the plastic strain and friction shear stress, it is seen that damage mechanisms in the different slip regimes are different. Finally, crack initiation location in the mixed slip regime is predicted based on the Smith–Watson–Topper multiaxial fatigue criterion. The predicted results are in agreement with the corresponding experiments.

Torsional Wear Behavior of MC Nylon Composites Reinforced with GF: Effect of Angular Displacement

The torsional wear behavior of monomer cast nylon (MC nylon) composites reinforced with glass fiber was studied with a self-made torsional friction tester. The worn surface of MC nylon composites was investigated with a scanning electron microscope. The worn surface of the steel disk was observed with a 3-D profiler. The experimental results indicated that the shape of torque–angular displacement (T–θ) curves changed from elliptic shape to quasi-parallelogram with the angular displacement increased from 5° to 30°. The serious wear characterized with a deep groove occurred at the position of about 1.5–4 mm radius of contact zone on the steel surface. The mass of MC nylon samples increased after torsional wear test. The torsional contact area can be divided into three zones: (a) a central stick zone, (b) an intermediate mixed-slipping annulus, and (c) a peripheral sliding annulus. The most serious wear occurred in the intermediate annulus because of the higher contact stress and mixed slip regime. The main wear mechanism of MC nylon samples was adhesive wear and abrasive wear. Plastic deformation of asperities was the character in the central zone. Slight adhesive wear was the main wear mechanism in the peripheral annulus.

Tribological behavior of polymethyl methacrylate against different counter-bodies induced by torsional fretting wear

Abstract A torsional wear and friction simulator with a ball on flat polymer was developed to analyze the tribological behavior of hip joints. Wear tests of polymethyl methacrylate (PMMA) against GCr15 (AISI 52100) steel and PMMA molecules (both with diameters of 40 mm) were conducted. Based on the analysis of frictional kinetics behaviors, and observations of three-dimensional (3D) profiles and SEM morphologies, the damage characteristics of PMMA were discussed in detail. With the increases of angular displacement amplitude, three types of torque/angular displacement amplitude ( T – θ ) curves (i.e., linear, parallelogram, and elliptical loops) were observed during the process of torsional fretting wear. In each of these loops, PMMA ran in a partial slip regime (PSR), mixed slip regime (MSR), and gross slip regime (SR), respectively. Compared to the PMMA/PMMA (P/P) counter-pairs, the boundary of the fretting regime of PMMA/GCr15 (P/G) counter-pairs shifted toward the direction of lower angular displacement amplitudes. The wear mechanisms of P/G counter-pairs included fatigue wear, oxidative wear, and adhesive wear; however, only abrasive wear was found for the P/P counter-pairs.

Introduction of a new sliding regime criterion to quantify partial, mixed and gross slip fretting regimes: Correlation with wear and cracking processes

Abstract Fretting is associated to small displacement amplitudes between two contacting surfaces subjected to vibrations. Depending on the contact loading (normal force, displacement amplitude…), different sliding regimes may arise: partial slip, mixed slip and gross slip. In this paper, the fretting behaviour of Ti-6Al-4V titanium alloy contact has been investigated. Sliding regimes are clearly defined through the analysis of the evolutions of an energy sliding ratio and the tangential force ratio. To accurately determine the sliding regime transition, a new criterion is introduced. It is defined as the proportion of gross slip cycles during the test (%GS). Fretting damage is also investigated though the analysis of crack lengths and wear volumes, compared to the sliding regime. The results show the relevance of this new sliding criterion to quantify the transition between partial, mixed and gross slip regimes. By comparing the values of this criterion and damage mechanisms, three steps have been defined in the competition between cracking and wear in the mixed slip regime. The first relates to a critical increase in cracks lengths, the second to a reduction of crack depths and the formation of a third body in the contact without ejection, and the last to the onset of wear by material removal.

Microstructural and tribological study of Nd:YAG laser treated titanium plates

In this work, the fretting behaviour of pure Ti plates laser treated with a Nd:YAG pulsed laser was compared to that of untreated Ti plates. Fretting tests were done at room temperature without lubrication. The contact geometry was a cylinder (bearing steel) on a plane. The evolution of both the ratio, μ = Q / P , between the normal and the tangential forces, and the Fouvry's energy criterion ( A ) were recorded as a function of the number of fretting cycles, N . Energy dispersive spectrometry and micro-Raman spectroscopy were used to analyse the fretting scars. The oxidized layer formed by the laser treatment displayed a mixed slip regime as a function of N , and a smaller fretting coefficient μ than the titanium reference.

Prediction of cracking in Ti–6Al–4V alloy under fretting-wear: use of the SWT criterion

Fretting occurs when two contacting surfaces are submitted to small amplitude displacements (few micrometers to few hundreds of micrometers). Depending on the normal stresses and the displacement amplitudes, two types of damage may occur: formation and ejection of debris or crack nucleation and propagation. In this study, we focus on the nucleation of cracks in Ti–6Al–4V alloy under fretting-wear loading (i.e. without bulk fatigue loading in the specimen). Our goal is to predict crack nucleation knowing the normal and tangential stresses and the materials properties. Cylinder on flat fretting-wear tests are performed with three different normal forces, two different cycles’ numbers and, for each cases, few values of the displacement amplitudes. All cylindrical and flat specimens are made of alpha–beta Ti–6Al–4V alloy. The effect of shot peening has also been investigated and, in this case, the two contacting specimens were shot peened. In all cases, the cracks in the flat specimen were analysed in polished cross sections. Cracks appear in the partial slip and the mixed slip regimes and these tests allow us to determine the minimal tangential force leading to crack nucleation for the given normal force and number of cycles. In order to predict the crack nucleation, the Smith–Watson–Topper criterion is used. This critical plane criterion is based on the calculations of the maximal normal stress and the maximal strain amplitude in the considered plane. The predicted location of the crack nucleation in the fretting scar coincides with the one observed in the fretting tests. To take into account the size effect in fretting, stresses are averaged on an elementary volume, which corresponds to the volume of an alpha grain. Shot peening is considered in the SWT criterion through an additional compressive stress, which reflects the compressive stress state induced by shot peening in the surface.