Wear Behavior of Aluminum Alloys at Slow Sliding Speeds

The investigated slow sliding speeds presented in this work enable the understanding of the wear behavior on aluminum alloys and could possibly facilitate the completion of the previously proposed wear mechanism map for aluminum at this slow sliding speed range. Dry sliding block-on-ring wear tests were carried out on aluminum alloys, AA5754 (Al-Mg), AA6082 (Al-Mg-Si), and AA7075 (Al-Zn-Cu), at a very slow sliding speed range (<0.01 m/s). A bearing steel ring of AISI 52100 was used as the counterbody. Tests were performed at varying contact pressures, 20, 100, and 140 MPa, and sliding speeds ranging from 0.001 to 1.5 m/s. The wear tracks and debris collected were examined by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD), with the aim of analyzing their morphology and composition. At relatively slow sliding speeds (>0.01 m/s), the specimens exhibited a wear process placed at the mild wear regime, characterized by oxidation and delamination mechanisms of both the aluminum specimen and the steel ring. However, at very slow speed range (<0.01 m/s), an increase in the wear rate and the friction coefficient is observed for all of the aluminum alloys, thus suggesting that an alternative wear mechanism could be taking place.     

Microstructure and Wear Behavior of a Manganese Bronze Bearing Material under Unlubricated Conditions

In an attempt to collect information about the tribological performance of copper-based bearings, the friction and wear behaviors of C86300 manganese bronze were investigated. The characteristics of the base material were determined by structural and mechanical investigations. Then, dry sliding pin-on-disc wear tests were performed against an AISI 52100 steel counterface. After the wear tests, the worn surfaces of the pins and wear debris were studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. In addition, light optical microscopy and microhardness measurements were performed for examination of the steel counterfaces and worn pin subsurface layers. With increasing normal load, the wear rate of commercial C86300 alloy (containing 0.6 wt% Si) decreased initially and then began to increase. After reaching a maximum wear rate at the load of about 60 N, the wear rate decreased again with a further increase in the normal load. However, the wear rate of this C86300 alloy mainly decreased with increasing sliding speed. Adhesive and abrasive wear were the dominant wear mechanisms under the designed conditions.     

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.     

Layer-Graded Cu/B4C/Graphite Hybrid Composites: Processing,Characterization, and Evaluation of Their Mechanical and Wear Behavior

In this article, we synthesized and studied functionally graded multilayered Cu/B₄C/graphite hybrid composites. Two classes of layer-graded composites were considered: pure Cu layer with two layers consisting of different particle sizes and uniform particle volume and a pure Cu layer with a single additional layer. The properties of the layer-graded composites were compared to those of single layer composites of two different particle sizes (1–20 µm and 60–90 µm). The composites were tested for compression strength, flexural strength, hardness, density, and wear and braking performance at a range of sliding speed conditions (5, 10, 30, and 35 m/s). The microstructure of the interfaces in the layer-graded composites was characterized to determine the quality of bonding. We found that the layer-graded composites possess improved compression and flexural strength due to lower porosity and residual compressive stress in the composite layer aided by the work-hardening of the Cu layer. The presence of the ductile Cu layer improves the toughness and crack resistance properties of layer-graded composites by macrostructure toughening mechanism. The layer-graded composites possess improved wear resistance and braking performance at both low and high sliding speed conditions due to reduced third-body wear, oxidation, and softening of composites, aided by effective heat conduction through the Cu layer. Finally, the wear mechanisms operating at various speeds were discussed with the help of microscopic and X ray diffraction studies.     

Bio-Fuel-Contaminated Lubricant and Hardening Effects on the Friction and Wear of AISI 1045 Steel

A study has been made on the wear and friction of hardened AISI 1045 steel using a tri-pin-on-disc type of friction and wear apparatus. During the investigation the linear pin wear, coefficient of friction and rise in pin specimen temperature were monitored and wear and friction curves plotted. Wear surfaces and mechanisms were investigated by means of optical microscopy. Analysis of used lubricating oil was performed using FTIR spectroscopy.

It was shown that the wear rate, type of wear and friction coefficient were influenced by contaminating the lubricant with bio-fuel as well as the surface hardening treatment. Corrosive wear and pits on the specimen surface were found when plain bio-fuel was used as lubricating oil. The results also confirmed that better wear resistance was obtained from the surface-hardened steel specimen with 4 % bio-fuel-contaminated lubricant.

Results from this study will be useful in material selection for tribological components in diesel engines running on vegetable fuel.     

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.     

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 Behavior of Thermally Sprayed Coatings under Different Loading Conditions

Wear behavior of three kinds of thermally sprayed coatings with similar hardness have been investigated under steady-state and dynamic loading tests. The steady-state loading tests were conducted on a reciprocating sliding device and the dynamic loading tests were conducted with a single-pendulum scratching device. Experimental results show that the wear mechanisms of the coatings under steady-state sliding friction testing are microcutting and microploughing, whereas the material losses under the dynamic impact scratch testing are mainly due to split cutting and fracture. Tribo-oxidization in the sliding process was found to have an influence on the wear behaviors of the thermally sprayed coatings. The results also indicated that wear resistance of thermally sprayed coatings can be correlated to hardness, plasticity, toughness, and cohesion. As far as the coatings of similar hardness were concerned, the wear resistance under steady-state loading was mainly due to the cohesion of the laminar structure of the coatings and the wear resistance under dynamic loading was mainly due to the toughness and deformation compatibility of the coatings.     

Monitoring of Wear Characteristics of TiN and TiAlN Coatings at Long Sliding Distances

TiN and TiAlN thin hard coatings have been widely applied on machine components and cutting tools to increase their wear resistance. These coatings have different wear behaviors, and determination of their wear characteristics in high-temperature and high-speed applications has great importance in the selection of suitable coating material to application. In this article, the wear behavior of single-layer TiN and TiAlN coatings was investigated at higher sliding speed and higher sliding distances than those in the literature. The coatings were deposited on AISI D2 cold-worked tool steel substrates using a magnetron sputtering system. The wear tests were performed at a sliding speed of 45 cm/s using a ball-on-disc method, and the wear area was investigated at seven different sliding distances (36–1,416 m). An Al₂O₃ ball was used as the counterpart material. The wear evolution was monitored using a confocal optical microscope and surface profilometer after each sliding test. The coefficient of friction and coefficient of wear were recorded with increasing sliding distance. It was found that the wear rate of the TiAlN coating decreases with sliding distance and it is much lower than that of TiN coating at longer sliding distance. This is due to the Al₂O₃ film formation at high temperature in the contact zone. Both coatings give similar coefficient of friction data during sliding with a slight increase in that of the TiAlN coating at high sliding distances due to the increasing alumina formation. When considering all results, the TiAlN coating is more suitable for hard machining applications.     

Friction and Wear Characteristics Due to Stick-Slip under Fretting Conditions

Friction and wear characteristics between two steel surfaces under fretting conditions are investigated experimentally. The fretting damage caused by low-amplitude oscillatory sliding can be classified into three regimes of gross-slip, mixed-slip, and partial-slip due to the stick-slip phenomenon. One of the most important characteristics of fretting wear is the transition from gross-slip to mixed-slip. Several criteria have been introduced for a quantitative determination of the transition between mixed-slip and gross-slip. However, the transition criteria have some problems in determining the regimes because parameters are difficult to calculate or depend on the system. To introduce new transition criteria in this study, the phase difference between friction force and relative displacement is used to determine the transition and predict the fretting wear. It is found that the phase difference with a range of 0° to 90° can predict the onset of fretting conditions.     

The Friction and Wear Model of Steels and Their Probable Statistic Calculations

Based on a systematic analysis of steel wear surfaces by Scanning Electron Microscopy (SEM) and Auger Electron Microscopy (AES), a statistical model for friction and wear of steels is proposed. Three categories of contact are proposed; oxide-oxide, metal-metal, and metal-oxide. Each category of contact is related to a probability distribution on the real contact area. Using a new concept of nascently exposed metallic surfaces, this paper derived the mathematical expressions for the friction coefficient and wear rate by means of statistical methods. The calculated values are in good agreement with measured values.     

Study of the Influence of Contact Geometry and Contact Pressure on Sliding Distance to Galling in the Slider-on-Flat-Surface Wear Tester

One of the major causes of tool failure in sheet metal forming is wear in the form of galling. Galling is gradual buildup of adhered sheet material on the tool and leads to unacceptable scratches on the sheet surface and to components that fail to meet tolerances. Because it is difficult to reproduce operational and interactional conditions in laboratory test equipments it is hard to test, model, and predict galling initiation.

Here the authors examine how changes from elliptical to line contact geometry influenced galling initiation under dry sliding by using a slider-on-flat surface (SOFS) wear tester. A micro clean tool steel was tested against ferritic low-strength and martensitic high-strength steel sheets.

The sliding distance to galling initiation was extracted from friction data and verified by scanning electron microscopy (SEM) observations. The presence of adhesive wear on worn tools after completed tests was used as a criterion. Experimental results showed that the elliptical contact causes galling quicker than the line contact.

Applicability of experimental results depends on the relevance of test conditions, so contact pressures calculated for the described tests were compared to calculated contact pressures in a semi-industrial U-bending test and to literature data relevant to industrial applications. Good agreement between values observed for SOFS and for most selected industrial applications was found, which assume that contact pressures typical for most common industrial applications can be successfully simulated by selection of tool geometry and normal load in the SOFS tester.     

Experimental Study on the Effect of Microstructure on Dry Sliding Wear Behavior of Titanium Alloy Using Taguchi Experimental Design

The present article depicts the influence of independent control factors such as microstructural variation, normal load, sliding velocity, and test duration on the dry sliding wear behavior of titanium alloy at room temperature using a statistical approach. Different heat treatments were carried out in a controlled manner to produce various microstructural features (i.e., lamellar, bimodal, and equiaxed) in this alloy. A lamellar microstructure is found to be harder than bimodal microstructure followed by an equiaxed microstructure in this alloy. Dry sliding wear tests were carried out using a multiple tribotester following a well-planned experimental schedule based on Taguchi's orthogonal arrays. The dry sliding wear behavior of this alloy consisting of various microstructural features is related to their hardness values. The results indicated that a lamellar microstructure has the lowest sliding wear resistance followed by bimodal and equiaxed microstructures. Using signal-to-noise ratios and analysis of variance (ANOVA), an optimal combination of control factors that minimize the dry sliding wear in this alloy were determined. Among all four control factors, normal load is the most significant control factor influencing the dry sliding wear behavior of the investigated titanium alloy, followed by microstructural variation, sliding velocity, and test duration. Normal load has a greater static influence of 39.53%, microstructural variation has an influence of 31.55%, sliding velocity has an influence of 21.6%, and test duration has an influence of 5.7% on the dry sliding wear of this alloy. Two wear mechanisms were identified: oxidative wear occurs at the lowest sliding velocity and delamination wear occurs at the highest sliding velocity. Optical microscopy, scanning electron microscopy, and Rockwell hardness measurements were used to characterize the microstructures in order to correlate the results obtained.     

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.     

The Coupling of Waviness and Heating in a Seal

Thermoviscous lubricant flow in seals and bearings is treated as a Couette flow, and a fully coupled perturbation flow, which results from waviness of the boundary, and which gives rise to uneven heat input into the solid boundaries. Differences in modes of heat transfer within the seal rings and out to the environment are separable, and determine the thermoviscous behavior of the film in a simple way. The temperature perturbation, or wave, in the film is an order of magnitude smaller than the perturbation of heat generation, justifying the assumption of isothermal and isoviscous flow.

Calculations show that materials such as C and SiC cannot be idealized as insulators when run against metals.     

钢铜摩擦副摩擦磨损特性的试验研究

本文试验分析了ＺＱＡ１９－４和ＺＱＺｎ６－６－３两种铜合金材料在不同的表面粗糙度下对摩擦系数和出口区油温的影响，以及改变载荷和相对滑动速度时，摩擦系数的变化状况。结果表明；铜合金成分不同时具有不同的硬度。     

湿煤粉条件下丁腈橡胶摩擦磨损规律的研究

国内外对橡胶材料在煤粉条件下的摩擦磨损特性尚缺乏研究,因而对丁腈橡胶在湿煤粉条件下的磨料磨损进行了研究,发现其磨损机理为疲劳磨损,磨损率随着法向载荷的增大而增大,随着放置速度的增大而减小;而摩擦系数则与法向载荷和旋转速度大致无关,其中水份在丁腈橡胶磨料磨损中主要起着三个作用：⑴对煤粉的粘结作用;⑵水膜的润滑作用;⑶降低瓣工作温度。     

Tribological Properties of Double-Glow Plasma Surface Niobizing on Low-Carbon Steel

The niobized layer was formed on Q235 low-carbon steel by double-glow plasma surface niobizing to improve its wear resistance. The microstructure, phase composition, and microhardness were determined. The friction and wear properties of the niobized samples and the untreated alloys were tested on a ball-on-disk tribometer by rubbing against GCr15 and silicon nitride (Si₃N₄) balls at room temperature and 400°C, respectively. The results indicated that the alloyed layer that contained a sediment layer and diffusion layer is about 35 μm in thickness, metallurgically adhered to the base metal. Niobium content was gradually decreased along the depth direction from the surface, which was similar to the change in the microhardness. The alloying layer mainly consisted of Nb, Fe₂Nb, and FeNb phases. Under unlubricated sliding conditions, the friction coefficients and the specific wear rates were lower than those of the untreated carbon steel at room and high temperatures. The wear mechanism of the niobized specimen at room temperature is dominated by slightly abrasive wear, whereas the predominant wear mechanism is abrasive wear and fatigue delamination at high temperature.     

Reciprocating Sliding Wear Performance of Hard Coating on Modified Titanium Alloy Surfaces

The high strength, low weight, and outstanding corrosion resistance properties possessed by titanium alloys have led to a wide range of successful applications in aerospace, automotive, and chemical industries and in power generation. Titanium alloys are characterized by poor wear resistance properties and their utilization has been excessive in nontribological applications. Surface texturing is a well-known and effective means of surface modification to improve the tribological properties of sliding surfaces. In the present work, modification of titanium alloy surfaces (Ti6Al4V) was done by lapping and laser surface texturing. The wear-resistant coating, AlCrN, was applied over the modified titanium alloy surfaces, with and without a chromium interlayer. Linear reciprocating sliding wear tests were performed with ball-on-flat contact geometry to evaluate the tribological performance of the coated alloy. The tests were performed under different normal loads for a period of 105 cycles at a frequency of 5 Hz. The friction force between the contact pair and displacement of the ball were simultaneously observed using a force transducer and laser displacement sensor. Optical microscopy was used to quantify the wear volume by measuring the wear scar diameter on both the specimen and the counterbody. Scanning electron microscopy (SEM) was employed to study the morphology of the wear scar. The characteristic behavior of the AlCrN coating such as bonding strength, wear volume, wear rate, and coefficient of friction with the chromium interlayer was evaluated and compared with the coating directly applied over the substrate. The coating on the textured surface, with the chromium interlayer showed better tribological performance.     

Acoustic Emission and Its Relationship with Friction and Wear for Sliding Contact

Further investigation of the relationships between friction and wear properties and the characteristics of acoustic emission was conducted in the case of dry and grease-lubricated sliding contact using a ball-on-cylinder testing apparatus. The effect of contamination simulated by the inclusion of glass bead particles was also explored. Experiments were performed at sliding speeds ranging from 0.09 m/s to 1.47 m/s, while maintaining a fixed load and duration. As a first observation and contrary to what could be expected, the higher speed did not contribute to the decrease in friction interpreted by a worsening of the starved regime that had a consequence of increasing wear. However, the results revealed a good correlation between the friction coefficient and acoustic emission (AE) rms voltage for dry sliding. Such a relationship may allow the prediction of a reasonable friction coefficient μ from an AE signal. It was also determined that the friction work correlated well with the corresponding integrated AE voltage over time, intRMS. The detection of the sliding speed threshold beyond which accelerated wear would occur was possible from the intRMS variation. Proportionality between the theoretically determined grease film thickness and the intRMS was observed.