The wear of martensitic stainless steel against tungsten carbide at temperatures up to 500 °C

The bearings in air motors of modern jet aircraft engines must operate dry in hostile conditions at temperatures up to 500 °C. One of the few metallurgical combinations which can function efficiently under these conditions is martensitic stainless steel on tungsten carbide. The work described was initiated to isolate the wear mechanism of such steels in contact with tungsten carbide at elevated temperatures. Experiments were carried out for pure sliding conditions (pin-on-disk experiments) and for rolling-sliding angular-contact bearings such as those used in practice. Wear rates were measured for both configurations for a series of loads, speeds and surface temperatures and extensive X-ray diffraction analyses were carried out on wear debris and on worn surfaces. Three distinct mechanisms of wear were established and found to be present in both configurations. These involve oxidation and abrasive wear at lower temperatures but become heavily dependent on material transfer as temperature increases. It is proposed from the results that the pin-on-disk experiments may be useful as a screening test for the selection of materials without the considerable cost of producing one-off angular-contact components. More evidence from other materials is, however, necessary to establish the validity of the test.     

Dry Sliding Wear Behavior and a Proposed Criterion for Mild to Severe Wear Transition of Mg–3Al–0.4Si–0.1Zn Alloy

Wear behavior of Mg–3Al–0.4Si–0.1Zn alloy was studied as a function of applied load and sliding speed under dry sliding conditions using a pin-on-disk configuration within 20–380 N and 0.1–4.0 m/s. An empirical wear transition map has been constructed to delineate the conditions under which severe wear initiated. The roles of microstructural evolution, hardness change in subsurface and surface oxidation on wear transition were also studied. The results indicate that the transition to severe wear occurs when the deformed microstructure in surface layer of material transforms into dynamic recrystallization (DRX) microstructure. A contact surface DRX temperature criterion for mild to severe wear transition is proposed, and the contact surface DRX temperatures are calculated using activation energy obtained by hot compression tests. A model for predicating mild to severe wear transition load has been developed based on the proposed contact surface DRX temperature criterion. The mild to severe wear transition loads are well predicted within the sliding speed range of 0.8–4.0 m/s.     

The relevance of wear-mechanism maps to mild-oxidational wear

The presence of oxygen in the environment in which a steel sliding system operates will promote a mild form of wear with wear debris consisting mainly of iron oxides. Of the oxidation-dominated mechanisms, mild-oxidational wear (the prefix describes the extent of oxidation and not the wear rate) has been most extensively investigated. In this paper, examples will be used to show that the wear-mechanism map for the unlubricated sliding of steels can adequately predict the occurrence of mild-oxidational wear and the trend of wear rates as well as describe the resultant features on the worn surfaces. It is also shown that this map is relevant to delamination wear and to test geometries other than the pin-on-disk configuration. It is suggested that the more-recently constructed wear maps for aluminium and magnesium alloys could similarly be used to predict the wear characteristics of these alloys during sliding.     

Physical Model of Tire-Road Contact Under Wet Conditions

Four non-halogenated ionic liquids (ILs) with trihexyl(tetradecyl)phosphonium cation are tested as lubricant additives to polypropylene (PP) and lithium-complex (LiX) greases. In pin-on-disk tests at elevated temperatures, the addition of an IL with bis(oxalato)borate ([BOB]) anion reduces wear by up to 50% when compared to the neat LiX base grease; an IL with bis(mandelato)borate ([BMB]) anion reduces friction by up to 60% for both PP and LiX. Elemental analysis reveals that oxygen-rich tribofilms help to reduce wear in case of [BOB], while the friction reduction observed for [BMB] is likely caused by adsorption processes. We find that temperature has a pronounced effect on additive expression, yet additive concentration is of minor importance under continuous sliding conditions. In contrast, rolling-sliding experiments at 90 °C show that the traction performance of LiX grease is dependent on additive concentration, revealing a reduction in traction by up to 30 and 40% for [BMB]- and [BOB]-containing ILs at concentrations of 10 wt%. Finally, an IL with dicyanamide anion reduces friction and increases wear in pin-on-disk tests at room temperature, while an IL with bis-2,4,4-(trimethylpentyl)phosphinate anion increases wear, showing only limited potential as grease additives. Overall, this work demonstrates the ability of non-halogenated ILs to significantly extend grease performance limits.

     

Experimental Analysis and Wear Prediction Model for Unfilled Polymer–Polymer Sliding Contacts

Lifetime prediction of polymer–polymer contacts is a major challenge. Current design methods stemming from metal contact surfaces lack accuracy because polymers behave differently, especially regarding temperature variations. Experiments were performed on a pin-on-disk setup alternating static and rotating elements. Common unfilled engineering polymers, viz. polyoxymethylene (POM), polypropylene (PP), polyamide 6.6 (PA6.6), and polycarbonate (PC) were tested at ambient and elevated temperatures. Material combinations were analyzed regarding the effects of load, velocity, temperature, and the product of contact pressure and sliding velocity (PV limit). The experimental results show that the PV limit is not predictive for polymer–polymer contacts; rather, each material combination has a critical factor that determines the wear and frictional values and thus the contact’s durability and lifetime. The critical factor is the value of contact pressure or sliding velocity or temperature at which there is sudden increase in wear rate. The experimental results also demonstrate that the application temperature in operation has an important influence on the lifetime. A temperature increase can either be beneficial or have a negative impact depending on the material combination. Resulting from the extensive experimental analysis, a new design method, based on the principle of deformation energy, is proposed. The new model is different from existing models because it includes thermal properties of the materials in contact and it makes use of the Péclet number. Because the proposed model requires only data sheet values and design parameters to predict wear volume, the model improves the support of engineers in designing durable polymer–polymer sliding contacts.     

浸渍磷酸盐石墨与9Cr18Mo不锈钢配副的摩擦磨损性能研究

针对航空发动机石墨密封常用的摩擦副浸渍磷酸盐石墨(M234Ao)和9Cr18Mo不锈钢材料,在UMT-TriboLab试验机上进行球-盘、销-盘接触摩擦试验,研究其低速轻载、高速重载工况以及干摩擦、油润滑下的摩擦磨损性能,利用接触式形貌仪、金相显微镜等对摩擦副表面进行观察分析,并分析其磨损机制。结果表明：在油润滑及面-面接触下的摩擦因数和磨损率明显低于干摩擦和点-面接触下;添加油介质可以降低界面摩擦剧烈程度,抑制金属氧化以及降低摩擦因数,特别是在高速重载工况下;M234Ao和9Cr18Mo配副间的磨损机制以磨粒磨损和黏着磨损为主,伴随有犁沟、微裂纹及擦伤现象。     

Wear of Silicon Carbide in Sliding Contact with Lubricated Thin-Film Rigid Disk

Silicon carbide (SiC) is a potential ceramic material for recording heads, yet its tribological performance against lubricated thin-film rigid disks is not fully known. Square pins with a 100 mm radius spherical surface were made from hot pressed SiC, chemical vapor deposited (CVD) SiC, and Al₂O₃TiC, and tested with lubricated thin-film disks. The pin-on-disk tests showed that the region of contact on the spherical surface of the SiC and CVD-SiC pins wears away to form a circular wear plateau with smears in and around the plateau. The wear plateau is formed rapidly in the first 1000 drag revolutions and then very gradually grows in size with further revolutions. Analysis of the smears showed that a large fraction of the smears contained SiO₂ which had been oxidized from SiC due to high temperatures generated at the pin surface in contact with the disk. In contrast, tests with Al₂O₃. TiC pins did not show any formation of a wear plateau on the pins.     

The response surface method and the analysis of mild oxidational wear

Instead of using the conventional oxidation theory to depict a disk’s wear rate as a function of contact temperature, the response surface method (RSM) is herein introduced to relieve the one-factor-at-a-time defect in portraying tribological characteristics. By means of a central composite design (CCD) technique, fewer operating conditions are needed to establish expressions for the wear rate parameter, the contact temperature and the friction coefficient as a function of sliding speed and applied load. A second degree polynomial was used to represent a curved surface which fits the experimental data. In addition to results for the designated operating conditions, wear rate parameters and contact temperatures obtained from the polynomials were compared with the experimental results. The activation energy in the wear rate expression can thus be derived as a function of sliding speed, applied load and contact temperature. The experimental data for the wear rate parameter can be expressed by smooth curves, instead of two different straight lines in two temperature subdivisions.     

Prediction of Wear in Reciprocating Dry Sliding via Dissipated Energy and Temperature Rise

An alternative technique aimed at facilitating the calculation of frictional power dissipation in reciprocating dry sliding is presented. The proposed technique can be employed for the prediction of wear in circumstances where the direct measurement of power dissipation is encumbered by practical limitations. Experimental tests are carried out to investigate the relationship between the system’s wear rate, power dissipation, and thermal response. A convenient technique is also proposed to estimate the average contact temperature in a reciprocating sliding contact. The predicted temperatures agree with the experimental measurements. It is also shown how the predicted temperatures can be used for the estimation of wear under reciprocating dry sliding configuration.     

An energy-based model for the wear of UHMWPE

An energetic approach to model the wear of tribological systems in which one of the components of the pair is polymeric is presented in this work. Experimental data, obtained in ultra-high molecular weight polyethylene (UHMWPE) pin-on-disk tribological tests, showed that a linear correlation between the wear rate of the polymer and the dissipated energy exists, independently of the lubricant, of the material used as counterbody and of the surface finishing of both polymer and counterbody. This fact strongly suggests that, in UHMWPE-based tribological systems, energy dissipation is mainly caused by the elasto-plastic deformation and wear of the polymer. Based on this assumption, it is developed a mathematical model that yields for a physical interpretation of the parameters of the experimental wear vs. energy correlation. These parameters are intrinsic wear properties of the polymer and can be used for the optimization of polymer-based tribological systems.     

Friction machine for testing materials under boundary lubrication

The design of a pin-on-disk friction machine intended for the testing materials under boundary lubrication has been considered. Engineering solutions involved in the development of the machine that are used to provide the precision of the adjustment of friction surfaces of specimens with regard to the counterface and to retain stable thermal conditions in the zone of contact at any duration of the test have been described. The machine is intended for carrying out wear tests of materials and coatings under various conditions, including conditions that correspond to the operation of shut-off valves of oil pipelines.     

A Wear Model of Plane Sliding Pairs Based on Fatigue Contact Analysis of Asperities

Wear modeling is essential to predict and improve wear resistance of machine parts. This article presents a fatigue wear model of plane sliding pairs under dry friction. The wear model is constructed through developing a dynamic contact model of surfaces and proposing a mean fatigue damage constant of asperities. It is simpler and more practical than existing fatigue wear models because it describes the quantitative relationship between the wear behaviors of the plane sliding pairs and the main factors including the load and sliding speed, material property, friction property, and surface topography of the pairs. Furthermore, the wear model can predict the wear of each component of the sliding pairs. Reasonability and applicability of the wear model are validated via pin-on-disc wear tests. The wear model is applicable to predict the wear of the plane sliding pairs, which is characterized by friction fatigue of contact surfaces. The wear model can also be used to guide the tribological design of sliding pairs in machinery.     

Determining local wear equation based on friction and wear testing using a pin-on-disk scheme

Based on pin-on-disk friction and wear testing, the parameters of the wear rate as a function of sliding velocity and pressure with account for their distribution over the contact spot are computed. The parameters are compared to those obtained assuming a uniform distribution of velocities and pressures. It is assumed in the work that the contact spot does not vary, the disk does not wear out, and the study is carried out under steady-state wear conditions.     

Artificial neural networks for predicting sliding friction and wear properties of polyphenylene sulfide composites

In this paper the potential of using artificial neural networks (ANNs) for the prediction of sliding friction and wear properties of polymer composites was explored using a newly measured dataset of 124 independent pin-on-disk sliding wear tests of polyphenylene sulfide (PPS) matrix composites. The ANN prediction profiles for the characteristic tribological properties exhibited very good agreement with the measured results demonstrating that a well trained network had been created. The data from an independent validation test series indicated that the trained neural network possessed enough generalization capability to predict input data that were different from the original training dataset.     

Effect of counterface roughness on abrasive wear of hydroxyapatite

The present study was undertaken to evaluate the effect of surface roughness of glass-infiltrated alumina on the abrasive wear of hydroxyapatite using a pin-on-disk tribometer. Hydroxyapatite was used as a model material to simulate tooth enamel. The wear tests were conducted in distilled water at room temperature using a constant sliding speed and three loads to model the normal occlusal contact conditions. The wear volume of polished hydroxyapatite pins increased by more than 20-fold as the average roughness of the alumina disks increased from 14 to 649 nm Ra. No measurable wear was detected on the alumina specimens. The wear surfaces were viewed in a scanning electron microscope (SEM) and were analyzed with X-ray dispersion spectroscopy to determine the extent of surface damage and the wear mechanisms. It is suggested that polished ceramic restorations will cause relatively low enamel wear, while increased roughness could severely abrade and damage the tooth enamel.     

Application and conceptual explanation of an energy-based approach for the modelling and prediction of sliding wear

Establishing an accurate predictive model for wear will result in major improvements in the efficiency, lifetime, cost and performance of many engineering systems. The authors have previously proposed a practical energy-based model to describe the tribological damage using energy dissipation. In this work, the capacity of this method to simplify the complex wear phenomenon was determined, and the applicability of this method to forecast the wear behaviour of materials was investigated. The wear results for a W–Cu electrical contact composite were utilised to determine the practical value of the model. Numerical integration of friction force–distance diagrams was used to evaluate the energy dissipation. Linear and non-linear least squares methods were applied to find the optimal curve fitting. It is shown that this model can be applied in two general forms: (1) a graphical method and (2) an explicit formulation. Both of these forms are shown to be capable of providing the necessary information, based on a limited number of initial tests, to predict unknown wear data (volume loss, lifetime, energy) without the need for morphological observations.     

Wear Prediction of Earth-Moving Machinery Joint Bearing via Correlation between Wear Coefficient and Film Parameter: Experimental Study

ABSTRACT

A wear life prediction of a grease-lubricated bearing in earth moving machinery has to be made based on actual wear data for its accuracy, but much effort should be devoted to obtain the wear data from the actual bearing. Currently, manufacturers provide a very conservative maintenance guide to schedule the replacement of the bearings to prevent the mechanical failure due to wear, causing economic losses, and the market requires finding optimal maintenance cycles to reduce maintenance costs. In this study, an economical wear prediction methodology for the grease-lubricated bearing based on typical pin-on-disk (POD) tests is proposed. POD tests were performed under boundary and mixed lubrication regimes considering the actual operating conditions of the bearings. It was found that there is a linear relation between the lubrication film parameter and the wear coefficient in log-log scale. The amount of wear of actual bearings was estimated by the wear coefficient from the linear regression analysis based on the POD test. The wear tests were further performed with the actual bearing under two loading cases and then the lubrication film parameter and wear coefficient were calculated, respectively. The estimated amount of wear shows good agreement with the measurement of wear depth. This leads us to conclude that it is possible to economically predict the wear amount in an actual bearing from POD wear test results by analysis of the correlation between the wear coefficient and the lubrication film parameter.     

Tribological behavior of polyetheretherketone, a thermotropic liquid crystalline polymer and in situ composites based on their blends under dry sliding conditions at elevated temperatures

The elevated temperature dry sliding friction and wear behavior of injection molded polyetheretherketone (PEEK), a thermotropic liquid crystalline polymer (TLCP), and in situ composites based on PEEK-TLCP blends were investigated. Results from sliding tests conducted on a pin-on-disk tribometer at selected temperatures within the range from 20 to 250°C are reported. Friction and wear mechanisms are related to the microstructure and phase behavior of the material systems investigated. TLCP concentration and thermally activated molecular relaxation processes are related to the mechanical properties and tribological performance of the PEEK-HX1000 blends. The potential of TLCP in situ reinforcement as a route towards the development of performance thermoplastic-based tribomaterials for high temperature use is discussed.     

Wear and Lubrication Behaviors of Cu-Based Friction Pairs with Asperity Contacts: Numerical and Experimental Studies

This paper aims to investigate the wear and lubrication behaviors of wet Cu-based friction pairs. A mixed lubrication model in plane contacts is developed, and the tests of pin-on-disk are carried out. Wear losses are measured by the oil spectrum analysis method. The wear loss, the real contact area ratio, and the load sharing ratio are analyzed. Effects of sliding velocity, temperature, and pressure are considered. The results show that the temperature is the most significant influence on the wear loss of lubricated Cu-based friction pairs. As the temperature rises from 30 to 150 °C, wear loss increases from less than 0.4 mg to about 2.3 mg. The wear factor of the lubricated Cu-based friction pair in asperity contact areas is \(K_{c} = 9.4 \times 10^{ - 9}\) (g/Nm). When the lubricated wear is slight, the oil spectrum analysis method is an effective approach to accurately determine the wear loss.     

High-Temperature Friction and Wear of Boron Steel and Tool Steel in Open and Closed Tribosystems

More and more components in automotive, material processing, and mining industries are operating under harsh conditions involving high temperatures and high contact pressures. Tribotesting for such applications is done using both open (one surface meeting a fresh countersurface) and closed (one surface follows the same track on the countersurface) test configurations. In order to enable development of new materials and processes intended for such conditions, there is a need for better understanding pertaining to tribological phenomena occurring under these different test configurations.

In this work, friction and wear characteristics of quenched and tempered tool steel sliding against boron steel (22MnB5) have been studied. The experiments were conducted using a specially designed hot strip tribometer (HST) under dry conditions at room temperature and 400°C in open as well as closed configurations. Scanning electron microscopy/energy-dispersive spectroscopy, and X-ray techniques were carried out to analyze the worn surfaces. Additionally, the results from the closed test configuration were compared to previous tests carried out with the same materials and parameters using a pin-on-disk (POD) test rig. The results have shown that wear was reduced at higher temperatures as well as with repeated sliding on the same contacting surfaces (i.e., closed configuration) compared to those with an open configuration. A good correlation of wear mechanisms and coefficient of friction between closed configuration tests and those carried out with the POD test rig were observed especially at 400°C.