Wear Transition Research Articles

Lessons learned from the test-to-test variability of different types of wear data

Contrary to the established principles of the scientific method, a surprising number of experimentally-based papers submitted to tribology journals and conferences report only one test result for each material pair or set of applied conditions. However, like hardness, yield strength, fatigue life, and other material properties, wear data exhibit varying degrees of repeatability and reproducibility (R/R). Repeatability concerns the replication of experiments within the same laboratory using the same equipment and materials. Reproducibility concerns testing on different equipment, usually at a different location, but using the same lot of specimens and procedures. An important question is: How many replicate measurements are needed to validate trends in wear behavior or to relatively rank materials, surface treatments, or lubricants? Without repeatability information, it is virtually impossible to establish whether reported material rankings or the effects of variables are real or fall within normal data scatter. The purpose of this paper is to characterize and analyze the R/R of wear data that result from a variety of sources, including material homogeneity, choice of units of measure, and choice of experimental variables. Case studies compare R/R for different forms of wear and their test methods, including ASTM standards. Lessons learned are presented for five forms of wear: (1) cavitation erosion, (2) three-body abrasion, (3) solid particle erosion, (4) dry sliding wear, and (5) fuel lubricity using the ball-on-cylinder (BOCLE) test. Wear transitions can also affect R/R. These examples provide insights for validating wear models, deciding how many repeated tests to make, and when ranking wear-resistance.

Effect of DC Magnetic Field on Friction and Wear Properties of 45 Steel at Different Velocities

In order to study the effect of Direct Current (DC) magnetic field on friction and wear properties at different velocities, dry sliding friction–wear tests of 45 steel friction coupled with or without magnetic field were conducted at different velocities on a pin–disk tribometer. The test results indicate that the friction coefficient is hardly influenced by magnetic field at various sliding velocities and decreases with the increase in sliding velocity. The magnetic field decreases the wear coefficient of 45 steel dramatically at low sliding velocity; however, it has little effect on wear coefficient at high sliding velocity. The sliding velocity range of oxidation wear of 45 steel is extended by magnetic field. At low sliding velocity, the magnetic field promotes the transition of adhesive wear to oxidative wear of 45 steel. While the sliding velocity is increasing, the ability of magnetic field capturing wear debris is weakening and the influence of magnetic field on tribological behavior and wear mechanism is decreasing. The analysis results of force model for wear debris in non-friction contact area indicate that the quantity of wear debris attracted on the disk is related to the size of wear debris, sliding velocity, magnetic flux density in friction contact area, permeability and remanence of material.

Dry Sliding Wear Behavior and Subsurface Microstructure Evolution of Mg97Zn1Y2 Alloy in a Wide Sliding Speed Range

The wear properties of Mg97Zn1Y2 alloy were investigated using the pin-on-disk wear machine within a load range of 20-380 N and a sliding speed range of 0.2-4.0 m/s. Analysis of worn surfaces using scanning electron microscope and energy-dispersive x-ray spectrometer revealed that wear mechanisms including abrasion + oxidation, delamination accompanied by heavy surface oxidation and delamination operated in mild wear regime, while wear mechanisms such as severe plastic deformation, severe plastic deformation accompanied by spallation of oxidation layer and surface melting prevailed in severe wear regime. The microstructural evolution and hardness change in subsurfaces were examined by optical microscopy and hardness tester. The transformation of surface material from the deformed into dynamic recrystallization (DRX) microstructure was observed before and after mild-to-severe transition. The reason for mild-to-severe wear transition was identified as the transformation of strain hardening to DRX softening in subsurface. Mg97Zn1Y2 alloy has a superior mild-to-severe wear transition resistance to AZ alloys because of its higher recrystallization temperature. A novel model for evaluating the critical surface temperature of mild-to-severe wear transition was established using DRX kinetics.

The tribological behavior evolution of TiB2/Al composites from running-in stage to steady stage

The purpose of this study was to investigate the characteristics of a friction and wear transition from the running-in stage to the steady-state stage for an Al-based composite containing TiB2 particles and fabricated by a pressure infiltration technique. The dry sliding friction and wear behavior was investigated using a 3.98mm diameter AISI 52100 steel ball-on-disk geometry under applied loads of 1N and 3N. Microstructural characterization and element distribution were carried out using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). 3D surface topographies and roughness of the wear surfaces were measured using confocal laser scanning microscopy (CLSM). The results indicated that the formation of a transfer film and boric acid (H3BO3) was the main reason for the low friction coefficient of about 0.16 at a load of 1N. An increase of friction coefficient was caused by the abrasion of pulled-out TiB2 particles. In the running-in stage at an applied load of 3N, abrasive wear dominated and resulted in the formation of grooves and pulled-out TiB2 particles. In addition, at a steady-stage friction coefficient of 0.6, severe three-body abrasive wear and oxidative wear were the dominant wear mechanisms. An excellent correlation was found between friction coefficient and surface roughness, as measured by 3D topography.

Refinement of tempered martensite structure and its effect on wear mechanism in SAE 8620

All mechanical components that undergo sliding or rolling contact are subjected to some degree of wear. Carburising treatment is important in improving wear characteristics of AISI 8620 gear steel. An experimental investigation was conducted on carburised AISI 8620 steel. Gas carburising of the specimens was carried out in sealed quenched furnace at 1198 K for 6 h followed by hardening at 1133 K, oil quenching at 393 K and followed by tempering at 453 K. Carburised cryotreated samples were cooled in a controlled manner soaked at 88 K for 16 h in a cryoprocessor subsequently followed by soft tempering at 373 K. Specimens were characterised by microhardness test, wear test and retained austenite content by XRD. 3D wear surface response and 2D contour map showed that wear rate decreased by 32% in the case of carburised cryotreated specimens as compared to only carburised specimens. It was concluded that there was an improvement in hardness and wear resistance of carburised cryotreated steel as compared to only carburised steel. Refinement and densification in martensitic structure resulted in shift in wear transition from severe wear regime to mild wear regime.

Friction and wear behavior of steam-oxidized ferrous PM compacts

This study determines density effect by assessing sintering temperature and graphite content on the dry sliding wear characteristics of steam-treated iron materials using a pin-on-disk wear test. The specimens were prepared from atomized premixed iron base powders and contained 0.1 to 1.0 wt.% carbon compacted at different densities (5.9 g/cc to 6.8 g/cc). The specimens were sintered for 1 h at different sintering temperatures (1090°C to 1130°C), and then subjected to continuous steam treatment at 540°C for 95 min through in situ Powder metallurgy (PM) technique. Steam treatment was proposed to improve the wear performances of the components of PM. Wear tests were conducted using a pin-on-disk-type machine. Load ranged from 20 N to 60 N. Sliding distance and sliding velocity of 312 m and 0.26 m/s, respectively, were adopted for all tests. Scanning electron microscope was used to analyze wear surface. Increased density and graphite content reduced the wear rate of steam-treated materials. Hardness increased with increasing graphite content. Wear mechanism, wear rate map, and wear maps were drawn for the test result data. Wear transition map identified mild, severe, and ultra-severe wear regimes as functions of applied load.

Relations of Counterface Hardness with Wear Behavior and Tribo-Oxide Layer of AISI H13 Steel

Dry sliding wear tests of AISI H13 steel (50 HRC) against AISI D2 steel counterface with three hardness levels (55, 50, and 42 HRC) were performed at 298 K to 873 K (25 °C to 600 °C). The relations of counterface hardness with the wear behavior and tribo-oxide layer of AISI H13 steel were explored. When sliding against the different-hardness counterface, H13 steel presents appreciably changed wear behavior as a function of temperature. For H d/H p (the hardness ratio of disk to pin) > 1, the wear rate increases with the increase of temperature, but the wear rate variation is roughly inversed for H d/H p < 1. For H d/H p = 1, the wear rate first decreases to reach the lowest value at 473 K (200 °C) and then rapidly increases with the increase of temperature. The lowest wear rate appears at 298 K (25 °C) for H d/H p > 1, at 474 K (200 °C) for H d/H p = 1, and at 673 K (400 °C) for H d/H p < 1. As no-oxide tribolayer exists below 473 K (200 °C), the wear behavior roughly complies with Archard’s equation; adhesive and abrasive wear prevail, regardless of H d/H p. As tribo-oxide layer exists at 473 K (200 °C) or above, the wear behavior depends on the tribo-oxide layer and thermal strength of the substrate, i.e., the stability of the tribo-oxide layer. Oxidative mild wear prevails at 473 K to 873 K (200 °C to 600 °C) for H d/H p < 1 and merely at 473 K (200 °C) for H d/H p = 1. However, a mild-to-severe transition of oxidative wear occurs at 473 K to 873 K (200 °C to 600 °C) for H d/H p > 1 and at 673 K to 873 K (400 °C to 600 °C) for H d/H p = 1. These findings suggest that the tribo-oxide layers are liable to exist stably for H d/H p ≤ 1 but to readily delaminate for H d/H p > 1.

Effects of gas pressure on microstructure and performance of (Ti, Al, Zr)N coatings produced by physical vapor deposition

In this study, a novel quaternary (Ti, Al, Zr)N coating was successfully fabricated via multi-arc ion plating technique on the Si3N4 ceramic substrate. A series of (Ti, Al, Zr)N coatings were produced on the silicon nitride (Si3N4) cutting tools by multi-arc ion plating technique using a combination of AlTi, pure Ti, and pure Zr targets. The effects of gas pressure on microstructure, deposition rate, coating thickness, phase constitution, mechanical properties, cutting performance, and wear mechanism of (Ti, Al, Zr)N coatings were systematically investigated by using four gas pressure values: 1.5, 2.0, 2.5, and 3.0Pa during the coating preparation process. It was observed from the flank worn surface that the main wear mechanism of the (Ti, Al, Zr)N coated Si3N4 cutting tools produced at different gas pressures was adhesion wear. At 1.5 and 3.0Pa, coating spalling occurred. When the gas pressure was 2.5Pa, the wear transition zone at the flank surface was obvious, which was confirmed to be positive toward the cutting performance of the cutting tools.

Effects of Loading and Sliding Speed on the Dry Sliding Wear Behavior of Mg-3Al-0.4Si Magnesium Alloy

ABSTRACTThe friction and wear properties of Mg-3Al-0.4Si alloy were investigated using a pin-on-disc tester. Morphologies and compositions of worn surfaces were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) for identification of the wear mechanisms. Microstructural evolution and hardness change in subsurfaces were analyzed by confocal scanning laser microscopy and hardness testing. The results revealed that the wear behavior of Mg-3Al-0.4Si alloy was classified into two types of wear regimes; that is, mild and severe. In the mild wear regime, wear rates increased at a low slope with increasing load; the corresponding wear mechanisms were oxidation, abrasion, and delamination. In the severe wear regime, wear rates increased rapidly at a high slope with load; the wear mechanisms were severe plastic deformation and surface melting. Analysis of microstructural evolution on the subsurface identified the reason for the transition from mild to severe wear; that is, the realization of dynamic recrystallization (DRX) in the surface layer material. A contact surface DRX temperature criterion for the mild to severe wear transition was proposed, and the critical DRX temperatures for the mild to severe wear transition were calculated using DRX kinetics.

Detecting Safety Zone Drill Process Parameters for Uncoated HSS Twist Drill in Machining GFRP Composites by Integrating Wear Rate and Wear Transition Mapping

The previous research investigations informed that the tool wear of any machining operation could be minimized by controlling the machining factors such as speed, feed, geometry, and type of cutting tool. Hence the present research paper aims at controlling the process parameters to minimize the drill tool wear, during the machining of Glass Fiber Reinforced Polymer (GFRP) composites. Experiments were carried out to find the tool wear rate and a wear mechanism map of uncoated High Speed Steel (HSS) drill of 10 mm diameter was developed for the drilling of GFRP composite laminates. The surface micrograph images on the drill land surface displayed dominant wear mechanisms induced on HSS drill during machining of GFRP and they were found to be adhesive wear, adhesive and abrasive wear, abrasive wear, and diffusion and fatigue wear. A “safety wear zone” was identified on the wear mechanism map, where the minimum tool wear of the HSS drill occurs. From the safety zone boundaries, it was inferred that the drill spindle speed should be set between 1200 and 1590 rpm and feed rate must be set within a range of 0.10–0.16 mm/rev for GFRP work and HSS tool combination to enhance the service life of 10 mm HSS drills and to minimize the tool wear.

Prediction of Tribological Limits in Sliding Contacts: Flash Temperature Calculations in Sliding Contacts and Material Behavior

In order to achieve greater efficiency or to meet light weight requirements, components are downsized. This, however, increases the load, e.g., Hertzian or nominal contact pressures and stresses of tribosystems. This load is expressed as pa·v-value, the product of nominal contact pressure and sliding velocity. pa·v-values are an effective tool for design engineers for predicting low wear/high wear transitions. Therefore, in the present work, topographical analysis has been combined with the plasticity of micro-asperities and the flash temperatures to estimate the limits of pa·v diagrams. The central piece of this set of models presented here is the calculations for flash temperatures and contact mechanics of micro-asperities. This central piece is used to predict the performance of materials in high velocity (turbines, machinery) and low velocity (human joint) applications. It is shown that the model combination suggested here is a useful tool for screening and preselecting a candidate and new materials with respect to tribological requirements before engaging in expensive testing.

Tribological characteristics comparison for oil palm fibre/epoxy and kenaf fibre/epoxy composites under dry sliding conditions

The aim of this study is to compare the tribological characteristics of OPF/E and KF/E composites in terms of fibre composition and temperature. A pin sample with a diameter of 10mm was made using the hot compaction technique. The dry sliding test was performed using a pin-on-disc tribometer. Increasing the temperature resulted in increased wear and decreased friction coefficient for both composites. The mild-severe wear transition of OPF/E accelerated with fibre composition although it produced a lower wear rate than KF/E at high-temperatures. In addition, the wear mode map for both OPF/E and KF/E composites has been proposed and addressed in this paper based on wear rate values. This mild-severe wear transition has been further confirmed by worn surface morphology.

Friction and Wear Behavior of 30CrMnSiA Steel at Elevated Temperatures

The friction and wear properties of 30CrMnSiA steel were investigated at elevated temperature from 100 to 600 °C. Thereafter, the wear debris and worn surfaces were examined to understand the wear mechanisms. The remained debris with relatively high hardness created three-body abrasion at lower temperatures (100-300 °C). Abrasive wear prevailed at the conditions with high friction coefficients and wear rates. A significant change in friction and wear behavior occurred at 400 °C. At the temperature of 400 °C, oxidation induced mild wear was found because of the formation of load-bearing oxide film. Both the friction coefficients and wear rates of the steel were lowest at 400 °C. At the temperatures of 500-600 °C, a mild-to-severe wear transition occurred which resulted in an increase in the friction coefficients and wear rates of the steel. This is related to the decrease in the strength of matrix and hardness of worn surfaces and subsurfaces. The predominant wear mechanism is considered to be severe abrasive, adhesive wear and a fatigue delamination of the oxide film.

Adhesion suppresses atomic wear in single-asperity sliding

We investigated the wear formation during a single-asperity sliding against a rigid substrate using molecular dynamics simulations. Two distinct wear mechanisms were observed: low-load atomic wear (isolated debris atoms or clusters) and high-load plastic wear (collective debris formation from plastic flow). The atomic wear rate depends on the normal stress exponentially, in agreement with the mechanically assisted bond-rupture theory. However, the plastic wear rate exhibits linear dependency on the normal stress. It was found that the asperity-substrate adhesion reduces the critical normal stress for the atomic-to-plastic wear transition, suppressing the atomic wear mode. Finally, a wear mechanism map of atomic/plastic wear was constructed in the domain of normal stress and adhesion, which is consistent with existing simulation and experimental results. This wear map could resolve the recent controversy on whether Archard׳s linear law is applicable for low-load tip wear.

The effects of TiC grain size and steel binder content on the reciprocating wear behaviour of TiC-316L stainless steel cermets

TiC-based cermets are heavily utilised in applications demanding good resistance to both wear and corrosion. In the current work, TiC-stainless steel (grade 316L) cermets have been developed, with the TiC grain size varied through heat-treatment, for steel binder contents between 10 and 30vol%. Microstructural analysis showed mean TiC grain sizes of ~4 and 10μm, respectively, for fine- and coarse-grained cermets, with the grain size nominally consistent as a function of binder content. Sliding wear resistance was assessed in a reciprocating motion, using a WC–Co counter face sphere paired against the TiC cermets. Overall, the fine-grained cermets exhibit better wear resistance and hardness. The specific wear rate was seen to increase with applied load and/or binder content, for both fine- and coarse-grained materials. SEM and FIB microscopy were used to assess the microstructural changes occurring during wear. A two- to three-body abrasive wear transition was apparent, together with the formation of a surface tribolayer, which highlights a further evolution to an adhesive wear mechanism. The tribolayer showed incorporation of a high concentration of O, which increased with the applied load, together with a predominance of the binder constituents.

Mild and Severe Wear of Titanium Alloys

Dry sliding wear tests were performed for TC4 and TC11 alloys on a pin-on-disk wear tester at room temperature and various sliding velocities. TC4 and TC11 alloys shared almost the same wear regularity as a function of sliding velocity and contact pressure. The titanium alloys were noticed to reveal not only severe wear, but also mild wear at room temperature. Severe and mild wear alternated to appear at the sliding velocity of 0.75–4 m/s. With an increase in the contact pressure, a mild-to-severe wear transition occurred at 1.5 and 2.68 m/s, especially significantly at 2.68 m/s. However, a mild wear appeared throughout at 0.75 and 4 m/s. When titanium alloys slid at 4 m/s and then at 2.68 m/s, the originally high wear rate at 2.68 m/s was markedly reduced. That is, a severe-to-mild wear transition occurred in the originally severe wear regime by means of pre-sliding at 4 m/s. The appearance of mild wear was confirmed to be attributed to the formation of tribo-oxide layers. Oxidative mild wear prevailed in mild wear regime; delamination wear did in severe wear regime.

Investigation on the Mild to Severe Wear Transition for AZ System Magnesium Alloys

Investigation on the Mild to Severe Wear Transition for AZ System Magnesium Alloys

Parametric Study of Dry Sliding Wear Behaviour of Functionally Graded Al LM25/Si3N4 Composite by Response Surface Methodology

Functionally graded aluminium LM25/silicon nitride composite was produced through stir casting followed by centrifugal casting and obtained a hollow cylindrical cast component with dimensions of 150 × 150 × 20 mm. The microstructural examination and the hardness test were carried out on the outer (1 mm) and inner surface (17 mm) as the function of radial distance from the outer periphery. The outer surface was observed with particle enriched region compared to inner surface and exhibited higher hardness. Hence the outer surface of the functionally graded composite was only further subjected to sliding wear test in pin-on-disc tribometer. The Central Composite Design in Response Surface Methodology was used to design the experiments for the selected parameters such as load (15–45 N), velocity (0.5–2.5 m/s) and sliding distance (500–2000 m). Regression test and Analysis of Variance were conducted to check the adequacy of the constructed model. The surface plots for wear rate showed that wear rate increased with increase in load and non-linearly varied with increase in velocity and sliding distance. Scanning Electron Microscopy analysis was conducted on the worn-out surfaces and observed mild to severe wear transition on increase of load.

Transition between mild and severe wear in titanium alloys

The mild to severe wear transition of two titanium alloys, Ti–10V–2Fe–3Al (a near-β titanium alloy) and Ti–6Al–4V (an α+β titanium alloy) was investigated and the correlation between the microstructure and wear micromechanisms was studied. Mild wear was dominated by oxidation via the formation and spallation of mechanically mixed layers (MMLs). The near-β alloy exhibited lower wear compared with α+β alloy in the mild wear region due to more stable MMLs as evidenced by 16% higher thickness of layer. Severe wear was characterized by strain localization and subsurface crack growth. Ti–6Al–4V showed lower transition load and lower resistance to unstable plastic deformation. However, Ti–10V–2Fe–3Al exhibited higher critical shear strain for subsurface crack initiation.

Wear transition of solid-solution-strengthened Ti–29Nb–13Ta–4.6Zr alloys by interstitial oxygen for biomedical applications

In previous studies, it has been concluded that volume losses (Vloss) of the Ti–29Nb–13Ta–4.6Zr (TNTZ) discs and balls are larger than those of the respective Ti–6Al–4V extra-low interstitial (Ti64) discs and balls, both in air and Ringer׳s solution. These results are related to severe subsurface deformation of TNTZ, which is caused by the lower resistance to plastic shearing of TNTZ than that of Ti64. Therefore, it is necessary to further increase the wear resistance of TNTZ to satisfy the requirements as a biomedical implant. From this viewpoint, interstitial oxygen was added to TNTZ to improve the plastic shear resistance via solid-solution strengthening. Thus, the wear behaviors of combinations comprised of a new titanium alloy, TNTZ with high oxygen content of 0.89mass% (89O) and a conventional titanium alloy, Ti64 were investigated in air and Ringer׳s solution for biomedical implant applications. The worn surfaces, wear debris, and subsurface damage were analyzed using a scanning electron microscopy and an electron probe microanalysis. Vloss of the 89O discs and balls are smaller than those of the respective TNTZ discs and balls in both air and Ringer׳s solution. It can be concluded that the solid-solution strengthening by oxygen effectively improves the wear resistance for TNTZ materials. However, the 89O disc/ball combination still exhibits higher Vloss than the Ti64 disc/ball combination in both air and Ringer׳s solution. Moreover, Vloss of the disc for the 89O disc/Ti64 ball combination significantly decreases in Ringer׳s solution compared to that in air. This decrease for the 89O disc/Ti64 ball combination in Ringer׳s solution can be explained by the transition in the wear mechanism from severe delamination wear to abrasive wear.