Characteristics of Extrusive Wear and Transition of Wear Mechanisms in Elevated-Temperature Wear of a Carbon Steel

The dry sliding wear of a medium carbon steel with different microstructures was measured under the normal load range of 50–150 N at 400°C by a pin-on-disc high-temperature wear setup. The wear behavior and wear mechanism were systematically studied; in particular, the characteristics of extrusive wear and the transition of wear mechanisms were investigated. Under low normal loads, the wear is oxidative type wear. Once the normal load reached a critical value, a mild-to-severe wear transition occurred, and subsequently an extrusive wear prevailed. The mild-to-severe wear transition depended on the microstructure of matrix; the critical normal load of the transition was 112.5 N for tempered sorbite, 125 N for lamellar pearlite, and 137.5 N for tempered martensite and tempered troostite. As oxidative wear prevailed, a thick oxide layer about 20–30 μ m and a plate-like wear debris with regular outline were recognized. However, as the extrusive wear occurred, the wear rate abruptly increased but the friction coefficient was reduced. The extrusive wear predominated due to thermal softening of the matrix and presented a superthin oxide layer (less than 0.5 μ m) and low oxide content on worn surfaces, accompanied by the appearance of ribbon-like wear debris.     

AZ系镁合金的轻微-严重磨损转变研究

为研究AZ系镁合金的轻微-严重磨损转变机制,在0.1~4.0 m/s的滑动速度范围内对AZ31和AZ51镁合金进行干摩擦试验。研究不同滑动速度下载荷对磨损率、磨损机制的影响,绘制磨损转变图,分析磨损亚表层组织与性能变化。结果表明:轻微磨损区的磨损机制主要包括氧化、磨粒和剥层磨损,严重磨损区的磨损机制则为严重塑性变形和表面熔化;在轻微-严重磨损转变前后,亚表层经历塑性变形-再结晶的组织转变和应变强化-再结晶软化的性能变化,磨损表层发生再结晶软化是导致轻微-严重磨损转变的主要机制,据此建立判定轻微-严重磨损转变的表面临界再结晶温度准则,利用再结晶动力学计算不同滑动速度下的表面临界再结晶温度和转变载荷。     

Embedding Wear Models into Friction Models

Frictional behavior in dry or boundary-lubricated tribosystems is commonly time-dependent. Examples include phenomena like running-in, scuffing initiation, adhesive transfer, coating wear-through, and lubricant starvation. Fundamental models for the sliding friction coefficient usually focus either on determining a steady–state value or on predicting periodic behavior like stick-slip. They often neglect the details of long- and short-period frictional transients, some of which are quite repeatable. In addition to generating heat, frictional work is known to be dissipated in several ways, including roughness changes, wear particle generation, tribomaterial evolution, and microstructural alteration. Pairs of materials can display identical average friction coefficients but significantly different wear processes because frictional work is dissipated differently from one pair of materials to the next. The attributes of friction-versus-time behavior for combinations of metals, ceramics, and polymers can be comprised of stages whose understanding may require the development of piecewise friction models that include wear. This paper discusses past work on the subject, exemplifies embedding a simple wear model into a friction-versus-time model, and indicates how friction process diagrams can play a role.     

Wear phenomenon in the hard steel machining using ceramic tools

The principle aim of this investigation is to recognize the wear phenomenon of the mixed ceramic tips against 60 HRC steel specimens in dry and hard turning operations. For this purpose both microscopic and microstructural aspects of ceramic tool wear were taken into consideration. Investigations were performed under varying feed rate, constant cutting speed of 100 m/min and small depth of cut of 0.2 mm to perform finishing cuts. Light optical microscopy (LOM), scanning electron microscopy (SEM), BSE technique and X-ray diffraction analysis (XRM) were applied for observations of worn tool surfaces, wear products and the distinction of wear mechanisms occurring. In general, wear mechanisms observed in the machining tests involve abrasion, fracture, plastic flow, material transfer and tribochemical effects which appear depending on the mechanical and thermal conditions generated on the wear zones. In particular, two types of transfer layer formation with different morphologies occurring at the rake-chip interface are distinguished.     

Wear Characterization of Mica-Loaded Al-Cu Dual Matrix Particulate Composites

In recent years, aluminum alloy-and copper alloy-based metal matrix composites are gaining importance in automobile and aerospace industries. Various reinforcements in particulate form can be used in aluminum alloy- and copper alloy-based metal matrix composites, one of which is mica. Mica has a layered or platy texture due to which it acts as a self-lubricating material. The objective of this investigation is to assess the influence of mica reinforcement on the tribological behavior of aluminum-copper (Al-Cu) dual matrix composites when quenched in different media. The results revealed that the compressive strength of mica-filled aluminum-copper (Al-Cu) dual matrix composites decreases as the percentage of mica increases up to 8% in all media. Compressive strength, Vickers hardness, and wear resistance of normalized and water-quenched specimens were greater than that of oil-quenched and non-heat-treated specimens. The worn surfaces of the samples were examined by scanning electron microscopy (SEM).     

Wear and Friction Characteristics of a Selected Stainless Steel

Dry sliding wear tests were performed for 3Cr13 steel with various tempered states at 25–400°C; wear and friction characteristics as well as the wear mechanism were explored. With an increase in test temperature, the wear rate decreased accompanied by an increase in tribo-oxides. The fluctuation of friction coefficient was slight at 25–200°C but became violent at 400°C. At 25–200°C, adhesive wear prevailed due to trace or less tribo-oxides; at 400°C, oxidative wear prevailed with the predominant tribo-oxides of Fe₃O₄ and Fe₂O₃. It can be suggested that the antioxidation of the stainless steel postponed the occurrence of oxidative wear to a higher test temperature. For adhesive wear, the wear resistance, roughly following Archard's rule, was directly proportional to hardness besides the specimen tempered at 500°C with grain boundary brittleness. But for elevated-temperature wear, a better wear resistance required thermal stability and an appropriate combination of hardness and toughness.     

Comparison of Three Laboratory Tests to Quantify Mild Wear Rate

Because the viscosities of engine and transmission lubricants are lowered in order to reduce hydrodynamic friction and thus energy consumption, it is important to ensure that wear rates do not increase and thus machine durability is not impaired. In practical terms this means that we require reliable methods for measuring the mild wear rates present in most lubricated machine components.

This article compares three mild wear reciprocating laboratory tests, one based on the high-frequency reciprocating rig (HFRR) and two on the mini-traction machine (MTM), in order to explore the extent to which wear rate is determined by the test configuration. The results show that some additive-containing lubricants including blends of antiwear additive and dispersant give quite consistent wear rates, independent of whether the surface is in continuous or intermittent contact, whereas others such as two friction modifiers do not. Possible reasons for these differences are discussed. The importance of accounting for wear during running-in and the need to remove any thick tribofilms present before quantifying wear volume are also confirmed.     

Comparative Study of Wear Behaviors of a Selected Titanium Alloy and AISI H13 Steel as a Function of Temperature and Load

A comparative study of the wear behaviors of a selected titanium alloy and AISI H13 steel as a function of temperature and load was performed on a high-temperature wear tester. The titanium alloy and H13 steel presented totally different wear behaviors with the variation in temperature and load. Their behaviors are suggested to be attributed to the protective ability of tribo-oxides and the thermal softening resistance of the matrix. Compared to H13 steel, the titanium alloy presented poor room-temperature wear resistance, excellent high-temperature wear resistance, and an extremely protective function of tribo-oxides.     

Wear Mechanisms in Galling: Cold Work Tool Materials Sliding Against High-strength Carbon Steel Sheets

Transfer and accumulation of adhered sheet material, generally referred to as galling, is the major cause for tool failure in sheet metal forming. In this study, the galling resistances of several tool steels were evaluated against dual-phase high-strength carbon steel using a SOFS tribometer, in which disc-shaped tools were slid against a real sheet surface in dry sliding test conditions. Three different frictional regimes were identified and characterized during sliding, and any transition in friction corresponded to a transition in wear mechanisms of the sheets. The performance of the tools depended on load, material and the particular frictional regime. Best overall performance was obtained by nitrogen-alloyed powder metallurgy tool steel.     

Wear mechanisms of laser-hardened martensitic high-nitrogen-steels under sliding wear

High-nitrogen tool steels (Fe, 15% Cr, 1% Mo, 0.3% C, 0.3% N) are applied, e.g. in bearings and gears in aeronautics and space technology. Their advantage compared to conventional, nitrogen-free tool steels is a superior corrosion resistance, which can be attributed to Cr, Mo, and N dissolved within the solid solution. In order to gain a sufficient toughness for application, these steels are tempered above 600°C bringing about precipitated carbides and nitrides, which bind Cr and N and, therefore, deteriorate the chemical properties. Within a DFG (German Research Council)-funded research project the authors show, that by means of laser hardening it is possible to dissolve a part of these precipitates — mainly nitrides resulting in improved properties under fatigue, wear and corrosion. This is brought about by a newly generated martensite with compressive residual stresses (fatigue, sliding wear), dissolution of Cr and N (corrosion) and a higher mechanical stability of the surfaces (sliding wear). This contribution focuses on the acting wear mechanisms under dry sliding wear. The investigations are carried out with pin-on-disk tests, with the disk as the actual specimen and a pin made of conventionally hardened 52100 bearing steel (100Cr6). It can be shown, that the wear properties of the high-nitrogen-steel are better than those of comparable conventional tool steels and that a laser treatment leads to a further improvement. Due to the fact that there is a tempered zone between overlapping laser-hardened areas, there is a change of acting mechanisms and, thus a distinct difference in wear rates. For the conventional corrosion resistant martensitic tool steel the difference between the tempered and the hardened zone is not as marked. Neither the wear mechanisms nor the wear rates differ distinctly. These effects and their influence on the wear behaviour is correlated with the microstructure of both steels before and after laser-hardening.     

Thermal-Induced Wear Mechanisms of Sheet Nacre in Dry Friction

Sheet nacre is a natural biocomposite with a multiscale structure including a mineral phase of calcium carbonate (97 wt.%) and two organic matrices (3 wt.%). The mineral phase is constituted by an arrangement of CaCO₃ biocrystal nanograins (ca 40 nm in size) drowned in an “intracrystalline” organic matrix (4 nm thick) in order to form a microsized flat organomineral aragonite platelet. These platelets are themselves surrounded by an “intercrystalline” organic matrix (40 nm thick) building up a very tough materials. This microarchitecture referred to as “bricks and mortar” nacre structure, is mainly studied for the creation of new organic/inorganic hybrid materials. Currently, only little is known about the nacre mechanical behaviour under dynamical loading and more particularly under tribological conditions which involve shocks and thermal effects simultaneously. This paper brings out the thermal-induced damage mechanisms effect on the wear of sheet nacre by the assessment of the thermal component of the friction with a scanning thermal microscope. Results reveal that the mean contact pressure is the main driving force involved in the degradation of the organic constituents. For the lowest mean contact pressure (<0.4 MPa), wear is rather weak because the friction-induced thermal component is not sufficient for degrading the organic matrices. In contrast, beyond 0.4 MPa, the friction-induced contact temperature rises up over the melting point of the organic matrices, and may even reach the temperature of the aragonite–calcite phase transformation increasing dramatically the wear of sheet nacre.     

Experimental Study of the Fretting Wear Behavior of Incoloy 800 Alloy at High Temperature

The fretting wear behavior of the nuclear power material Incoloy 800 was investigated in this study. A PLINT high-temperature fretting tester was used on an Incoloy 800 cylinder against a 304SS cylinder at vertical cross contact under different temperatures (25, 300, and 400°C). During testing, a normal load of 80 N was applied, and the displacement amplitudes ranged from 2 to 40 µm. The fretting wear mechanism at high temperatures and the kinetic character of the materials of the Incoloy 800 steam generator tube were analyzed. Results showed that the fretting running regimes varied little with ncreasing temperature, and some microcracks were observed in both the mixed fretting regime (MFR) and the partial slip regime (PSR) at high temperatures. Slight abrasive wear and microcracks were the main wear mechanisms of the Incoloy 800 alloy in PSR, whereas those in the MFR and the gross slip regime were oxidative wear, abrasive wear, and delamination.     

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

The 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.     

Reciprocating Sliding Wear Behavior of 60NiTi As Compared to 440C Steel under Lubricated and Unlubricated Conditions

ABSTRACT

60NiTi is a hard (～60 HRC) and highly corrosion-resistant intermetallic with a relatively low elastic modulus (～100 GPa). In addition, this alloy exhibits a high compressive strength (～2,500 MPa) and a high elastic compressive strain of over 5%. These attributes make this alloy an attractive candidate to be employed in structural and mechanical component applications. However, sliding wear behavior of this intermetallic has not yet been studied in a systematic way. In this study, lubricated and unlubricated reciprocating sliding wear behavior of 60NiTi is compared to 440 C steel as a conventional bearing and wear-resistant alloy. Results of experiments carried out under different loads show that 60NiTi, despite having a higher hardness, exhibits a significantly inferior wear behavior under dry conditions in comparison to 440 C steel. These unexpected results indicate that 60NiTi does not follow conventional wear theories where the wear of materials has an inverse relationship to their hardness. On the other hand, under lubricated conditions with castor oil and a synthetic gear oil, 60NiTi exhibits low specific wear rates. These results exhibit the importance of proper lubrication in sliding mode applications where 60NiTi is exploited as a wear-resistant alloy.     

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.     

Investigation of the Transition State in the Wear of Polyphenylene Sulfide Sliding Against Steel

The effect of sliding variables, including counterface roughness, sliding speed, and contact pressure, on the run-in state of wear and friction was studied. Sliding was performed in the pin-on-disk configuration with a polyphenylene sulfide (PPS) pin resting on the flat steel counterface. Some experiments were also run to study the effect of air cooling and heating. Optical microscopy and scanning electron microscopy were used to study the shape and size of the wear debris, worn pin surface, and the transfer film formed on steel counterfaces. It was found that friction and wear in the run-in state were significantly affected by the sliding variables studied and their influence was closely related to the development of a transfer film during the run-in state. If the transfer film developed during initial sliding, the coefficient of friction increased and wear rate decreased. The wear rate in the run-in state increased with the increase in initial counterface roughness and there was an optimal counterface roughness of 0.06 m Ra for minimum steady state wear rate. A higher applied load led to a higher wear rate in the run-in state but that was not the case with steady state wear rate.     

Influence of PP-g-MA Compatibilization on the Mechanical and Wear Properties of Polypropylene/Thermoplastic Polyurethane Blends

Polypropylene/thermoplastic polyurethane (PP/TPU) blends of different weight ratios (75/25 and 25/75) were processed by melt blending using a maleic anhydride–grafted polypropylene (PP-g-MA) copolymer as coupling agent. The influence of the amount of the coupling agent (0, 3, 5, 7, 9, 11 phr) on the mechanical, frictional, and wear properties of the blends were characterized through tensile test, three-point bending, dynamic mechanical analysis (DMA), and ball-on-disc wear tests. PP-g-MA was found to be an effective compatibilizer for PP/TPU blends, and mechanical and wear properties of the blends were proved to be strongly impacted by the amount of coupling agent. Tensile strength of the blends tends to increase with increasing the PP-g-MA content and 9 phr is found to be optimal for both concentrations of the blends. Good miscibility of the blends with increasing compatibilizer content was also verified by DMA. From the wear test results, the compatibilizer was found to be more effective in PP₇₅/TPU₂₅ blends, in parallel with the results of the mechanical tests. The PP₇₅/TPU₂₅ blend with 11 phr PP-g-MA content was superior to the other blends. In addition, in this work, a new model based on image processing is proposed that provides accurate and fast wear rate measurement and detailed information of the wear track, especially in heterogeneous materials. Using the model, the homogeneity of the wear track widths was proved to be strongly impacted and improved by the use of a coupling agent.     

Wear transitions and mechanisms in lubricated sliding of a molybdenum coating

Wear tests were performed for a Mo coating sliding against bearing steel specimen under boundary lubrication conditions. Results were compared with (i) hardened carbon steel sliding against bearing steel and (ii) Mo coating sliding against boron cast iron. Tests indicated that the wear resistance of the Mo coating was superior to that of the uncoated hardened steel. The initial surface topographies of the coatings were suitable to facilitate the transfer of the applied load directly onto the phases and prevented the softer phase directly involved in the wear process. The morphology of the transfer layer formed on the Mo coating was identified by X-ray diffractometry. And the layers were expected to supply an in situ lubrication effect. The wear rates of the coating against a steel slider were lower compared with those worn against a cast iron slider. With increasing applied load, the probability of the harder phases crack and fracture increased until the fraction of the unfragmented phases on the contact surfaces was no longer adequate to support the load. The dominant wear mechanisms in each wear regime were discussed.     

贝氏体钢板与普碳板耐磨性对比试验

本文介绍了热轧低碳贝氏体高强钢板在QLK800．32型斗轮取料机上与普碳钢板进行耐磨性对比工业试验的情况。试验结果表明,贝氏体高强钢板的耐磨寿命可达到普碳板的3倍以上。     

An Investigation on Reasons Causing Inferiority in Unlubricated Sliding Wear Performance of 60NiTi as Compared to 440C Steel

60NiTi is gaining recognition as an alternative to 440C steel in ball bearing components due to its intrinsic corrosion resistance and unusually high static load capacity. 440C steel and 60NiTi exhibit comparable Rockwell hardness and would be expected to exhibit similar sliding wear behavior using hardness based models. However, results show that under unlubricated sliding conditions, 60NiTi shows inferior wear properties than 440C steel. In this study, a series of indentation and single pass scratching experiments are conducted to elucidate the reasons behind this unexpected observation. Moreover, sliding wear tests carried out under moderate and extreme tensile stress conditions were used to identify sliding conditions under which these materials exhibit similar and dissimilar behavior. The results show that 440C steel exhibits more microscopic plasticity than 60NiTi, halting the propagation of generated tensile microcracks. In contrast, the intrinsic brittleness of 60NiTi leads to the formation and growth of microcracks between the shear bands causing subsequent wear particle generation. These lead to the occurrence of wear through more aggressive abrasion processes in 60NiTi than 440C steel. These findings help explain why 60NiTi performs well when lubricated. 60NiTi is expected to tolerate ～912?MPa tensile stress before yielding. Under good lubricated conditions where a perfect lubricating film is formed, friction induced tensile stresses fall below the tensile strength of 60NiTi and wear is prevented. However, inadequate lubrication combined with high contact stress leads to damage and wear.