Comparative tribological evaluation of journal bearings

Performance of sliding bearings with reeled bimetallic bushes of three different bronzes was compared with the performance of solid bushes of aluminium alloy with a view to replacing aluminium bushes in gear pumps by reeled bimetallics. a set of tribological selection criteria was proposed and comparative investigations were carried out.     

The effect of silicon content and morphology on the wear of aluminium-silicon alloys under dry and lubricated sliding conditions

Improvement in the efficiency of the internal combustion engine has resulted in the increased usage of aluminium alloys and, in particular, aluminium-silicon as a substitute for cast iron. Despite the wide use of such materials in tribological environments little knowledge is available on the wear resistance of aluminium-silicon alloys. This paper investigates the wear performance of a range of binary aluminium-silicon alloys produced by a novel melt-spray technique. In addition, samples of the 11wt% silicon alloy were produced by conventional casting methods to elucidate the influence of silicon morphology on wear resistance. Pin-on-ring wear tests were carried out under dry and boundary-lubricated conditions. Surface analysis showed a similar wear mechanism under both conditions, these being: (1) oxidative and (2) metallic wear. Under boundary-lubricated conditions the load at which the transition to metallic wear occurred was increased. Raising the silicon content of the alloy was reflected in an increase in both wear resistance and transition load. Under dry sliding conditions the wear rate of the 11wt% alloy increased with a reduction in the silicon particle size, whereas under boundary-lubricated conditions the reverse was observed and the sand-cast alloy exhibited superior performance.     

Effects of sliding velocity and applied load on the tribological mechanism of amorphous poly-ether–ether–ketone (PEEK)

In this work, the effects of sliding velocity and applied load on the tribological characteristics, i.e. friction coefficient and wear rate, of an amorphous poly-ether–ether–ketone (PEEK) coating was examined. Friction tests were performed on a ball-on-disc apparatus. Based on analyses of the worn tracks, a comprehensive attempt is made to approach the tribological mechanism of amorphous PEEK. A hypothesis is proposed that the tribological behaviour of the amorphous PEEK is closely related to its viscoelastic behaviour. The sliding velocity plays significant roles on the tribological characteristics by influencing the interface temperature and strain rate of the PEEK surface layer involved in the friction process. The applied load influences the tribological performance by varying the strain range in the surface layer.     

Effect of reinforcement on wear behaviour of aluminium hybrid composites

Abstract

Aluminium metal matrix composites are among the recent developments in engineering applications to meet the present day need of light weight, high strength/weight ratio and good wear properties. In the present study, AlSi10Mg alloy reinforced with 3, 6 and 9 wt-% alumina with constant 3 wt-% graphite particles was produced by stir casting technique. Microstructural investigations as well as evaluation of mechanical properties such as hardness, tensile strength and double shear strength were conducted on composites and unreinforced alloy specimens. Tribological behaviour of hybrid composites was studied using pin on disc test machine. Wornout surfaces were analysed using scanning electron microscopy, and wear debris were analysed using X-ray diffraction. Results revealed that the mechanical properties of hybrid composites were higher than unreinforced alloy. Dry sliding wear test results indicated that the aluminium alloy reinforced with 9 wt-% alumina and 3 wt-% graphite has highest wear resistance compared to unreinforced alloy.     

The influence of alumina particle dispersion and test parameters on dry sliding wear behaviour of zinc-based alloy

The present investigation deals with dry sliding wear characteristics of a zinc-based alloy (ZA 37) with and without Al₂O₃ particle dispersion over a range of sliding speeds and applied pressures. The matrix alloy has been examined under identical test conditions in order to examine the role played by the second phase alumina particles on wear behaviour. The observed wear behaviour of the samples has been explained in terms of specific characteristics like cracking tendency, lubricating, load bearing and deformability characteristics, and thermal stability of various microconstituents. The nature of predominance of one set of parameters (causing higher wear rate) over the other (producing a reverse effect) was thought to actually control the wear behaviour. Examinations of the characteristic of wear surfaces and subsurface regions also enabled to understand the operating wear mechanism and to substantiate the wear behaviour.At low sliding speed, significantly lower wear rate of the matrix alloy over that of the composite was noticed. This has been attributed to increased microcracking tendency of the composite than the matrix alloy. Reduced wear rate and higher seizure pressure experienced by the composite over that of the matrix alloy at the higher sliding speeds could be explained to be due to enhanced compatibility of matrix alloy with dispersoid phase and greater thermal stability of the composite in view of the presence of the dispersoid. The maximum temperature rise due to frictional heating has been observed to be low in the case of matrix alloy than composite at low speed while the trend reversed at higher speeds. In general, the wear rate and temperature increased with applied pressure and speed. Seizure pressure reduced with increasing speed while the seizure resistance (pressure) of the matrix alloy was more adversely affected by speed than that of the composite.     

Tribological behaviour of carbon and low alloy steels: effect of mechanical properties and test conditions

Abstract

In this paper, the effects of mechanical properties and test conditions on the tribological behaviour of ISO C45 carbon steel and ISO 42CrMo4 low alloy steel were studied. The tribological tests were carried out, without lubrication, on a reciprocating friction tester. Cylinder on flat contact configuration was adopted. The results showed that there is no obvious relationship between the mechanical properties and the friction ones. However, the variation in the coefficient of friction depends on the test conditions. In contrary to normal load, the effect of sliding speed on the coefficient of friction is not the same for the two steel nuances. The tribological properties are dependent, however, on the nature of wear debris.     

Improvement in tribological performances of magnesium alloy using amide compounds as lubricating additives during sliding

The tribological characteristics of a magnesium alloy, AZ91D (die-casting), are investigated in a sliding lubricating system using various amide compounds as lubricating additives on a Timken type tester against a bearing steel (AISI52100) ring. Results indicate that a significant improvement in the tribological performance exists using the amide compounds as additives. The number of amido group (–CONH₂) in additive molecules and the molecular structure of amide compounds have significant effect on the tribological characteristics of magnesium alloy. Electromicroscopy reveals that the mild abrasive wear is a predominant wear mechanism of magnesium alloy using an amide additive while the dominated wear mechanism is a severe abrasive wear with severe material deformation using only base oil. Observation shows the formation of boundary film on the magnesium alloy. XPS analysis suggests the occurrence of tribo-chemical reactions between Mg and amide compounds with the formation of chemically stable compound (or complex) of magnesium and amide, as well as the formation of friction polymer.     

Correlation Between Tribological Parameters and Wear Mechanisms of Homogeneous and Heterogeneous Material

This study intended to investigate the effect of tribological parameters on wear mechanisms and friction coefficient for homogeneous and heterogeneous materials. Particularly, effects of particle geometry and normal load on the tribological behaviour of an aluminium alloy and nodular cast iron have been developed. These materials are used in two industrial applications. The first one is used to transport granular material. It has been shown that damage of used truck’s buckets is produced. However, the nodular cast iron is used in automobile industry thanks to its lower density, good wear resistance and its low friction coefficient. A scratch test was used and the wear mechanisms were observed for different attack angles. The normal load was also varied and correlation between wear mechanisms, tribological parameters and friction coefficient was highlighted.     

Slurry abrasion response of surface engineered Ti6Al4VELI

Titanium alloys, by virtue of their outstanding combination of properties, continue to evolve as direct replacements for steels in offshore production systems to meet the challenging offshore application conditions. However, the wider use of titanium and its alloys is frequently retarded by their reputation for poor tribological behaviour. It is because of this simple engineering scenario that comparative tribological behaviour of surface engineered Ti6Al4VELI in abrasive slurry has been evaluated to identify treatments capable of improving its wear behaviour. To best simulate potential application conditions, sliding wear tests were carried out using a block-on-wheel test configuration in abrasive mud slurry. The wear volumes lost from the surface engineered Ti6Al4VELI test blocks ranged from negligibly small for substrates plasma sprayed with either WC–Co, Ni–Cr or Mo, to approximately twice that measured for a steel test block in the cases of untreated, shot peened, electroless Ni plated and anodised Ti6Al4VELI. Hard chrome plated material and thermochemically treated material demonstrated a certain degree of wear, which however, was significantly less than that found for the steel block.     

Tribological Performance Optimization of Electroless Ni–P Coatings Using the Taguchi Method and Grey Relational Analysis

The present article considers an experimental study of tribological performance of electroless Ni–P coatings and optimization of tribological test parameters based on the Taguchi method coupled with grey relational analysis. A grey relational grade obtained from the grey relational analysis is used as performance index to study the behaviour of electroless Ni–P coating with respect to friction and wear characteristics. Experiments are carried out by utilizing the combination of tribological test parameters based on L₂₇ Taguchi orthogonal design with three test parameters, viz., load, speed and time. It is observed that all the three test parameters have significant contribution in controlling the friction and wear behaviour of electroless Ni–P coating. In addition, the interaction of load and time has significant influence on tribological performance. The surface morphology, composition and wear mechanism of the coatings are studied with the help of scanning electron microscopy, X-ray diffraction analysis and energy dispersed X-ray analysis.     

Mechanical and tribological properties of a novel aluminum bronze material for drawing dies

A new aluminum bronze material with aluminum content over the solubility limit and several trace elements, Cu-14Al-X alloy (X is trace elements), has been developed for drawing dies. The mechanical properties such as hardness, tensile strength and impact toughness were evaluated experimentally. The friction and wear behavior of the material was investigated under boundary lubrication conditions. The experimental results demonstrated that the developed alloy possessed higher tensile strength and hardness, lower friction coefficient and wear rate, compared to currently used aluminum bronzes, therefore it is expected to replace conventional iron-based materials that are commonly used for drawing dies. With the excellent anti-friction property and high carrying capacity, the new material, Cu-14Al-X alloy, will be able to provide precision drawing dies.     

Effect of microwave heat treating processing on frictional behaviour of aluminium alloy 2900 composites

The sliding wear behaviour of microwave processed, SiC_p and Al₂O_3p reinforced aluminium alloy 2900 and 2024 metal matrix composites prepared by powder metallurgy method was investigated in a pin on disc system. The objective is to determine the effects of novel alloying elements of AA 2900, ceramic addition and microwave aging process on the strength to tribological properties. This composite is evaluated to be an effective replacement for conventionally available AA 2024 composites in brake applications. Compared to conventional heat treating processes, microwave processing used for heat treating the samples is observed to be novel method in improving the strength–microstructural–tribological properties. AA 2900 with 6 wt-% Al₂O₃ exhibited good strength to microstructure relationship with excellent wear characteristics compared to AA 2024 composites which are governed by alloying elements in AA 2900. 2 H aged AA 2900 with 6 wt-% Al₂O₃ sample exhibited good frictional coefficient values with good density and strength characteristics. Hence, it is observed that alloying elements in AA 2900 and microwave processing have enhanced the strength to tribological behaviour where the property enhancement is achieved only through ceramic reinforcements.     

Wear and frictional mechanisms of copper-based bearing alloys

The present study investigated the role of alloy microstructure and surface roughness on wear and friction behavior of leaded and unleaded tin bronzes. Ball-on-disk experiments were carried out under dry conditions with steel balls sliding against bronze disks. Scanning electron microscopy (SEM), energy dispersive electron microscopy (EDX), x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy were performed to analyze the sliding tracks and the ball scars. The wear reducing effect of lead was associated to the formation of an oxidized lead rich layer. When no such film formed on the leaded bronze wear was more severe than in case of unleaded bronze. Nevertheless, the presence of lead in the alloy was a necessary but not sufficient condition to obtain a smeared layer and thus a lubricating effect of the leaded alloy. Two mechanistic hypotheses were formulated to explain the formation of the smeared layer.     

An investigation on sliding wear behavior of PVD coatings

Ti-6Al-4V alloy rubbing against aluminum-bronze 630 was evaluated in this work. High velocity oxygen fuel (HVOF) WC-10%Co-4%Cr thermal sprayed and TiN, CrN and DLC physical vapor deposition (PVD) coatings were applied to increase titanium substrate wear resistance. Pin-on-disk tests were performed with a normal force of 5 N and at a speed of 0.5 m/s, with a quantitative comparison between the five conditions studied. Results showed higher wear resistance for Ti-6Al-4V alloy DLC coated and aluminum-bronze 630 tribological pair and that the presence of graphite carbon structure acting as solid lubricant was the main wear preventing mechanism.     

Wear characteristics of metals

Although there are still many gaps in our knowledge of the factors involved in tribological interactions, there is sufficient information available to characterise the commonly encountered wear mechanisms. Many techniques are currently available to modify surfaces to improve their wear characteristics, but these are usually applied after a problem has become apparent in service. These techniques are not usually included in the original design because most engineers do not appreciate the effect of operating conditions on the life of components. The precise role of physical and mechanical properties of metals in wear is little understood. Much effort has been expended in our understanding of bulk properties. Considerably more effort is now required to understand surface properties. Halling has stated that the major growth area for the next decade lies in the role of surface treatments for improving tribological characteristics²⁴. These, however, are already becoming available faster than our rate of understanding of their precise tribological properties.Design guides for widely used engineering metals in different conditions of treatment are required under specific wear conditions. Few materials combinations have been examined in the metallurgical detail demonstrated by Lea. This approach should be further extended to produce wear maps with their associated atlas of surface and sub-surface microstructure showing both satisfactory and unsatisfactory wear behaviour.An appreciation of the cost wear would bring about a greater awareness of the problems involved and greater effort would be applied to producing long term solutions instead of the concentration on short term expediencyThe major problem, however, is the lack of communication between those with the knowledge and those who should be using it in their designs. The tribologist should produce more information related to the behaviour of materials in service. He should be encouraged to publish more case studies and solutions related to specific engineering components or systems.     

Wear behaviour of flame sprayed NiCrBSi coating remelted by flame or by laser

Flame spray coatings are widely used in industry because of low cost and process simplicity. However, high porosity and poor adherence to the substrate means that quality is poor, though it can nevertheless be improved by subjecting coatings to a remelting using a technique that usually involves an oxyacetylene flame. The study that follows is an attempt to evaluate a laser technique as an alternative to the more traditional flame remelting of flame spray layers, using grey cast iron (DIN GG30) as the substrate and a NiCrBSi alloy as the coating material. Coatings obtained by laser remelting exhibited a practically pore-free microstructure with good adherence to the substrate. The limited control of process parameters during flame remelting led in some cases to incomplete melting of the full thickness of the layers. Hardness of the remelted coatings was very similar in both cases, with values that were slightly lower than for flame-spray layers. The tribological behaviour of both coating types was then compared in dry sliding wear tests (block-on-ring tests) at various loads (30–100 N) and sliding speeds (0.65–2.62 m/s). Both coatings wear rates and wear rate coefficients k (mm³/Nm) were calculated. No significant differences in wear performance between the two coatings were found. A severe wear regime with adhesion as the principal component was observed at the higher test loads. The predominant wear mechanism at the lower test velocities was oxidation.     

Dry sliding wear behaviour of an aluminium alloy–granite particle composite

In the present study, the effect of granite reinforcement on the dry sliding wear behaviour of an aluminium–silicon alloy (BS:LM6) was investigated using a pin-on-disc machine. The composite was prepared using liquid metallurgy technique wherein 10 wt.% granite particles were incorporated in the matrix alloy. Sliding wear tests were conducted at applied loads in the range 0.2–1.6 MPa and speeds of 1.89, 3.96 and 5.55 m/s. The matrix alloy was also prepared and tested under identical conditions in order to see the influence of the dispersoid phase on wear behaviour. It was observed that the composite exhibited lower wear rate than that of the matrix alloy. Increasing applied load increased the wear rate. In the case of the composite, the wear rate decreased with speed except at higher pressures at the maximum speed; the trend reversed in the latter case. On the contrary, the matrix alloy exhibited minimum wear rate at the intermediate test speed. Seizure pressure of the composite was significantly higher than that of the matrix alloy, while temperature rise near the contacting surfaces and the coefficient of friction followed an opposite trend. SEM examination of the worn surfaces, subsurface regions and debris enabled to understand the operating wear mechanisms.     

Influence of T4 Heat Treatment on Tribological Behavior of Za27 Alloy Under Lubricated Sliding Condition

The effects of heat treatment on the microstructure, hardness, tensile properties, and tribological behavior of ZA27 alloy were examined. The alloys were prepared by conventional melting and casting route. The heat treatment of samples included the heating up to 370 °C for 3 or 5 h, quenching in water, and natural aging. Lubricated sliding wear test were conducted on as-cast and heat-treated ZA27 samples using block-on-disc machine. The friction and wear behavior of alloys were tested in contact with steel discs using combinations of three levels of load (10, 30, and 50 N) and three levels of linear sliding speeds (0.26, 0.50, and 1.00 m/s). To determine the wear mechanisms, the worn surfaces of the samples were examined by scanning electron microscopy (SEM). The heat treatment resulted in reduction in the hardness and tensile strength but increase in elongation. The heat-treated alloy samples attained improved tribological behavior over the as-cast ones, under all combinations of sliding speeds and contact loads. The rate of improvement increased with duration of solutionizing process before quenching in water. Obtained tribological results were related to the effects of heat treatment on microstructure changes of alloy.     

Si3N4-hBN陶瓷复合材料与Fe-B合金配副的摩擦学特性研究

利用MMU-5G销-盘式端面磨损试验机考察Si3N4-hBN陶瓷复合材料与Fe-B合金配副分别在干摩擦和水润滑条件下的摩擦磨损性能,分别采用扫描电子显微镜( SEM)、激光扫描显微镜(LSM)、X光电子能谱(XPS)、X射线能谱(EDS)和X射线衍射(XRD)分析摩擦面及磨屑的形貌与物质组成.结果表明,hBN的加入未能有效地改善Si3N4-hBN/Fe-B合金摩擦副的摩擦学性能,干摩擦条件下,Si3N4-hBN摩擦表面微凸体与Fe-B合金中的硬质相Fe2B发生碰撞而导致脆性断裂和剥落,发生磨粒磨损,摩擦因数均高于0.9,磨损率均高于10-5 mm3/ (N·m)数量级;水润滑条件下,由于水流带走了磨屑,避免磨粒磨损的发生,为Si3N4-hBN摩擦表面发生化学抛光提供条件,化学抛光使销、盘试样的摩擦表面变得光滑,从而获得较为优异的摩擦学性能.     

The effect of substrate properties on tribological behaviour of composite DLC coatings

The unique features of DLC coatings in providing low friction and low wear and, at the same time, causing low wear to the counterface make them very attractive in industrial applications, in improving tribological performance of mechanical components on various substrates. In this study, composite DLC coatings have been deposited on sintered ferrous alloy, M42 tool steel, 2618 aluminium alloy, and 6063 aluminium extrusion substrates using the combined CFUBMS–PACVD technique. The effect of mechanical properties of substrate materials on tribological behaviour of the composite DLC coatings has been investigated at various loads on a ball-on-disk wear machine in dry air. A transition load was usually observed for coatings on the various substrates except for the aluminium extrusion; above the transition load the coating was completely destroyed via some spallation/fragmentation process after 2 h sliding, and the wear rate increased dramatically with further increase in load. The coating system on sintered ferrous alloy substrate exhibited the highest transition load among the four types of substrates studied. This is considered to have resulted from the combined effects of the lower elastic modulus of the porous sintered ferrous alloy substrate, which decreases the stress concentrations in the contact region, and the surface roughness and porosity, which enhance the bonding strength between the coating and the substrate under multi-contact conditions. The high elastic modulus of the tool steel substrate leads to tensile stress conditions in the sliding contact region and therefore makes coatings deposited on such a substrate more prone to breakdown/fragmentation, resulting in a transition load close to that for coatings on the soft 2618 aluminium alloy substrate. For coatings on the 6063 aluminium extrusion substrate, significant plastic deformation occurred in the substrate at loads above 1.5 N. However, despite the heavy deformation in the substrate, coatings on this substrate were not scraped off, as were coatings on the 2618 aluminium alloy substrate, even at a load as high as 20 N. The specific wear rate increased continuously with load, no apparent transition load being explicitly identifiable. This study shows that hard DLC coatings can be applied on both hard and soft substrates for improvement of the tribological behaviour of mechanical components.