Friction and wear of friction composites reinforced by natural fibres

In the present work, friction material composites were proposed to be used as automotive friction materials. The composites were reinforced by agricultural fibres of corn, palm, and sugar bars. The conventional friction materials based on asbestos cause serious lung diseases and being cancerous potential. The aim of the present work is to replace them by the proposed composites because they are environmentally friendly friction material for brake lining and clutch facings. Agricultural wastes of sugar bars, corn and palms fibres were prepared to obtain fibres of length less than 5 mm. The fibre materials were mixed by carbon, barium sulfate, silica, metallic powders and phenol formaldehyde. The proposed composites were pressed in the die at 105°C temperature. The produced specimens were subjected to machining processes to obtain the cylindrical form of 8 mm diameter. Experiments were carried out using test rig designed and manufactured to measure both friction and wear. It consists of a rotating hollow flat disc made of carbon steel, with an outside diameter of 250 mm and 16 mm thickness. The experiments investigated the effect of agriculture fibre wastes (corn, sugar bars, and palms fibres) on friction coefficient and wear. Wear mechanisms of the proposed composites were characterized by scanning electronic microscopy. The tribological properties of the proposed composites materials were compared to three commercial brake linings. Based on the experimental results it was found that, addition of agriculture fibre wastes (corn, sugar bars, and palms fibres) to composites materials increased friction coefficient and decreased wear. Friction coefficient slightly increased, while wear drastically decreased with increasing fibres content. The maximum friction value (0.58) was obtained by composites containing 30 wt.% iron and 25 wt.% sugar bar fibres. The corn fibres were more compatible with aluminum powder where it gave the highest friction coefficient and relatively lower wear compared to other composites. Wear resistance of the tested composites containing bunches and aluminum represented the lowest values among composites containing corn and bunches fibres. The lowest wear values were observed for composites containing 25 wt.% corn fibres and 30 wt.% aluminum and composites containing 20–25 wt.% sugar bar fibres.     

Tribological behaviour of proposed polymeric bearing materials

The aim of the present work is to introduce new polymeric bearing materials. The proposed polymeric composites are consisting of polyethylene (PE), polypropylene (PP) and polystyrene (PS) and filled by fibres of polytetrafluoroethylene (PTFE) in concentration up to 25 wt.% as well as different types of natural oils such as (corn oil, olive oil, paraffin oil, glycerin oil, castor oil and sunflower oil) in concentration up to 10 wt.%. The frictional behavior of the proposed composites and wear resistance are investigated at different values of applied load. Based on the experimental observations, it was found that for composites free of oil, friction of PS and PE specimens decreased, while friction of PP specimens slightly increased with increasing PTFE content. PP composites filled by corn oil showed slight friction increase. Besides, friction coefficient displayed by PS and PE specimens filled by glycerin oil decreased with increasing oil content, while friction coefficient displayed by PP specimens showed consistent trend. It was noted that, PE filled with 7.5% glycerin oil and 20 wt.% PTFE displayed the minimum value of friction coefficient (0.07). This friction coefficient values recommend those composites to be used as bearing materials. PE filled by glycerin oil displayed relatively lower friction values due its common known good lubricating property. Friction of PE composites filled by paraffin oil drastically decreased with the increasing oil content. PP composites showed the lowest wear values. In addition to that, it was shown that wear displayed by composites filled by glycerin oil was higher than that containing corn oil, while wear of the tested composites filled with olive oil showed lower values than that displayed by corn oil filled composites. Composites containing 5.0–7.5% paraffin oil content showed good wear resistance which recommends them to be used as bearing material. Wear of PP, PS and PE composites filled with sunflower oil and 15 wt.% PTFE drastically decreased with increasing oil content. The minimum wear was displayed by PP and PE composites filled with 10% oil content.     

Effect of processing parameters and graphite content on the tribological behaviour of 3D printed acrylonitrile butadiene styrene

3D printing is nowadays used not only to rapidly produce prototypes, but is further applied for the fabrication of functional parts. Amongst other factors, processing parameters such as scaffolding angle and raster gap greatly affect the behaviour of such printed parts. Little attention has been given so far to the tribological behaviour of such prints. In this study the above mentioned parameters on the friction behaviour, in terms of friction coefficient and wear rate, is investigated. For this purpose the Fused Deposition Modelling is used as one of state of the art 3D printing methods. Graphite flakes were further added to the reference acrylonitrile butadiene styrene (ABS) matrix in an attempt to enhance the properties. Results show that the scaffolding angle only affects the behaviour, if a positive printing gap is applied – when a negative gap is used, the angle has no significant effect on properties. Maximum coefficient of friction at acceptable values of specific wear rates can be attained at a scaffolding angle of 90° with negative gap. The incorporation of graphite further increases the friction coefficient on the expense of reduced wear properties.     

Verschleißschutz für Titanbauteile

Wear Protection for Titanium Components The use of titanium and its alloys in the last decades keeps on increasing due to its material‐specific characteristics like high firmness, good corrosion characteristics and very high thermal maximum stress. However nowadays, the use of titanium components in systems where wear resistance is important is limited by titanium’s relatively low wear resistance. Surface wear is in principle a characteristic, conditioned by chemical and physical effects of the elements involved as well as collective stress. The necessity for new systems where good wear resistance and excellent mechanical properties are combined keeps on showing up. Due to titanium’s tendency to react with surrounding media, titanium alloys are difficult to be welded. Embrittlement by admission of hydrogen and oxygen can occur at high temperature processes or even changes on titanium’s microstructure may appear. Brazing techniques, which are actually applied to steel, have been modified and adapted for using them to titanium materials. Here, commercially available braze pastes and hard materials where combined and applied on titanium.     

Entwicklung hochverschleißbeständiger wolframschmelzkarbidbasierter Schichten auf Aluminiumbauteilen durch Plasma‐Pulver‐Auftragschweißen

Development of high wear‐resistant FTC‐based coatings on aluminium components using plasma transferred arc welding Nowadays, functional surfaces of components can be effectively protected from extreme wear with the help of fused tungsten carbide (FTC) coatings. The wear protection of steel components using FTC has been well known for many years. This paper presents the feasible study of improving the wear resistance of aluminium components with FTC particles using plasma powder arc welding. The FTC coatings are developed with two methods: one is the dispersion of carbide particles in aluminium and the other one is the combination of dispersing and alloying of FTC‐based composite powders. In this research, coatings within a thickness range of a few millimeters are developed with varying process parameters and compositions of the filler materials. The developed coating systems are tested with regard to their specific properties and their wear resistance. Finally, their application potential is presented.     

Mechanical and wear performance evaluation of tungsten added Co‐30Cr‐4Mo‐1Ni biomedical alloy with Taguchi optimization

Development of biomaterial with diverse properties (physical, mechanical, wear, and many others) for hip femoral head is one of the most exigent tasks. Improper material often causes component failure during functioning. Therefore, in this study, a series of implant materials containing tungsten of different weight percentages were fabricated by high temperature vacuum casting induction furnace and the physical, mechanical, and wear properties were examined. The proportions were varied from 0 wt. % ‐ 4 wt.% in a cobalt–chromium alloy (Co‐30Cr‐4Mo‐1Ni). The mechanical properties were tested by the micro‐hardness tester and the compression testing machine, while the wear performance was analyzed through a pin‐on‐disc tribometer under different operating conditions at room temperature. Initially in this study, steady state experimental analysis was performed to obtain the volumetric wear loss and coefficient of friction by varying sliding velocity and normal load respectively. Afterwards, the Taguchi experimental design has been conducted to obtain the optimum wear response. Lastly, scanning electron microscopy and atomic force microscopy were utilized to analyze the contour of wear mechanism and 3D surface topography. From the results obtained, it was found that Co‐30Cr‐4Mo‐1Ni‐2 W implant material provides the best combination of the properties for a given application.     

Friction and wear properties of polyphenyl ester and graphite filler in the carbon fibre‐reinforced ultra‐high‐molecular‐weight polyethylene composites

Ultra‐high‐molecular‐weight polyethylene (UHMWPE) reinforced with carbon fibre (CF) underwent an enhancement of heat and wear resistant with the addition of polyphenyl ester (POB) and graphite, respectively. The effect of graphite content on the tribological properties of the composites was studied. The wear surface was examined using scanning electron microscope (SEM). The results of the sliding wear tests showed that with graphite loading, wear resistance increased and the coefficient of friction was much more stable. In addition, graphite improved the tribological properties of the composite. Hardness, impact strengths and thermal stability of the composites were enhanced. With increased load, the wear rate of the ultra‐high‐molecular‐weight polyethylene+carbon fibre+polyphenyl ester+10 % graphite composite tended to increase, whereas the coefficient of friction decreased. The adherence and plastic deformation were dominant wear mechanisms for the ultra‐high‐molecular‐weight polyethylene+carbon fibre+polyphenyl ester+graphite composites. The formation of a thin and uniform transfer film was observed.     

The effect of aging treatments on wear behavior of aluminum matrix functionally graded material under wet and dry sliding conditions

This study investigated that the effect of aging treatments on wear behavior of functionally graded material (FGM) that was reinforced via being integrated with aluminum 2014 alloy (AlCu4SiMg) and 15 vol% SiC. The specimens were obtained via centrifugal casting technique, and then two different aging treatments were applied. Wear experiments were applied at 1.256 m/s constant sliding velocity, under two different loads and two different sliding distances for each condition via a pin‐on‐disc wear apparatus. The variations that occurred on wear behavior of cast and aged materials were analyzed. The results show that the minimum wear loss values were obtained under dry sliding conditions due to the aging processes. On the other hand, with increasing sliding distances under wet sliding conditions, the aging processes' effect was decreased on wear resistance.     

Tribologische Untersuchung bionischer und mikrostrukturierter Funktionsflächen

An established concept adjusting tribological properties and for increasing the wear resistance is presented by coatings. In addition to the material adaption of surfaces, there are efforts of applying structures on tool active parts in order to allow a further adjustment on the property profile. For this reason, the presented article investigates the influence of bionic and technologically textured surfaces on the friction and wear behavior with and without near‐net shaped wear‐resistant PVD coatings. Based on the example of nature, a honeycombed surface structure discovered on the head of scarab beetles as well as a dimple structure optimized for the manufacturing time were transferred on HSS steel by means of micro‐milling. The analyses focus on the influence of the surface structures, the effects of PVD coatings and their interactions on the friction and wear behavior. The investigations show that the tribological properties depend on each surface structure and the material pairing. Both the technological and the bionic structures show a reduction of the friction coefficient in combination with the material pairing 100Cr6 and WCCo compared to polished samples. Furthermore, it is shown that the CrAlN coating has no influence on the friction behavior, but rather leads to the desired increase in the wear resistance.     

Einfluss der Mikrostruktur auf das Verschleiß‐ verhalten der hartanodisierten Aluminium‐legierungen EN AW‐6082 und EN AW‐7075

Microstructural effect on the wear behaviour of the hard‐anodised aluminium alloys EN AW‐6082 and EN AW‐7075 The suitability of hard‐anodising of high‐strength Al alloys (EN AW‐7075‐T651) for the fabrication of protective coatings which are also applicable on screws was investigated. A medium‐strength AlSi1MgMn alloy (AA60682‐T6), generally rated as applicable for anodising, was used as reference material. After possible setting phenomena of a screw joint, the load‐bearing surface of the screw can be subjected to an oscillating relative movement. The damaging tribological load was simulated in an oscillation wear test. The resulting wear appearances have revealed that the untreated oxide coatings on the EN AW‐6082 substrate are not capable of providing protection against tribological load. Since hot‐water sealing increases the hardness of the coating but also contains the technology‐induced risk of softening the substrate material, other tribological protection methods have been looked for. The analysis of the tribological tests (characterisation of the structure and the resulting properties of the material, measurement of the wear amount and analysis of the wear appearance) have shown that the films sealed with wax emulsion on both substrate materials are the most promising candidates for the application of devices under oscillation wear. The obtained roughness, friction coefficients and hardness values confirm the positive behaviour of the anodically oxidised EN AW‐7075‐T651 alloy under the chosen tribological load.     

Tribological properties of Ta‐C‐N and Ta‐N thin films

The amorphous Ta‐C‐N and Ta‐N thin films were deposited using magnetron sputtering on silicon wafer under the similar condition. The as‐prepared thin films were characterized using scanning electron microscope (SEM), optical profiling system, nano‐indentation and friction test instruments. The results show that, compared with the Ta‐N thin film, the Ta‐C‐N thin film has higher nano‐hardness (9.45 GPa) and elastic modulus (225.71 GPa). Furthermore, the lower friction coefficient and wear rate of the Ta‐C‐N thin film are 0.238 and 5.94×10^–6 mm^–3· N^–1·m^–1, respectively. The wear surface of Ta‐C‐N thin film is smoother than that of the Ta‐N thin film. Therefore, it shows better anti‐wear properties.     

Untersuchungen zum Verschleißverhalten von Metall/Metall – Gleitpaarungen aus CoCrMo‐Legierungen

Investigation of the Wear Behaviour of Metal/Metal Bearings of Co Cr Mo – Alloys CoCrMo‐alloys are successfully used for long‐term implants, because of their corrosion and wear resistance as well as their mechanical properties. In order to improve CoCrMo‐alloys for metal‐on‐metal bearings the influence of carbon content on wear behaviour is investigated. Casted or forged CoCrMo‐alloys with a carbon content from 0.008 to 0.48 wt % were studied in ring on disc oscillating tests. Friction torque, weight loss and surface roughness, as well as light and scanning electron microscopic investigations of the sample surface were used to characterize the wear behaviour. – All alloys show similar friction torque and weight loss. But the surface roughness and the wear mechanisms are depended on the carbon content.     

Verifizierung numerischer Verfahren zur Modellierung abrasiver Verschleißprozesse durch Berechnung von Scratchtests

Verification of numerical methods for modeling abrasive wear processes by calculating scratchtests Abrasion is a fundamental wear mechanism. It occurs whenever surfaces are loaded tribologically by hard particles or roughness peaks. The scratch test shows the behavior of a surface during abrasive stress. For that purpose a diamond tip (indenter) moves onto the material with either constant or progressive normal force. At first the material will be deformed elastically; with increasing force plastic deformation occurs till crack‐ and chip‐forming, depending on the ductility of the material. Using elastic and plastic indentation depth, friction, acoustic emission through cracks and the three‐dimensional analysis of the scratch, wear resistance to scratch‐stress can be characterized. The simulation of scratch tests is useful to verify material models comparing the relative easily and quickly accomplishable tests with the simulation results. Based on this verification new or existing material approaches can be adapted even better to applications. The article describes problems and solutions during implementation of the simulation of the scratch test for the steel C45 (normalized). The comparison with experimental results shows that this approach is successful. In the future a closed material model for this type of stress will be developed.     

High temperature wear testing of a Ni‐based superalloy pin on a cast iron disc

A pin‐on‐disc wear test rig is described, which allows to extract reproducible mechanical and microstructural wear data from very small sample volumes at temperatures up to 900°C. The friction and wear behavior of Alloy 80A against a cast iron is evaluated at temperatures from ambient to 800°C. The wear rate of Alloy 80A decreased with increasing temperature. This was attributed to the development of protective tribolayers, which prevented a direct contact between the two sliding partners. Energy Dispersive X‐Ray (EDX) mapping of surface wear products and Transmission Electron Microscopy (TEM) results for the evolution of subsurface microstructures are exemplarily presented for wear experiments performed for 10 min at 300°C (frequency: 20 Hz, load: 20 N, stroke: 1 mm). EDX investigations provide a good insight into material transfers and oxide layer generations during sliding wear. TEM‐micrographs revealed cell structure formation and very small nanograins directly beneath the surface.     

Verschleißbeständige induktiv hergestellte Beschichtungen (InduClad)

The lifetime of abrasive stressed components can be extended by coating. Deposition welding and also the new method InduClad are suitable procedures for the production of thick layers. Both these technologies were compared and their advantages and disadvantages were assessed. The results from wear investigation are considered as a final evaluation. Special attention will be paid to material‐technique aspects of the application of welding technology previously unusable like ionic or covalent bonded hard materials. Also, alternatives are presented to conventional metal‐matrix‐composites and especially the embedding of hard materials in metallic matrices will be evaluated. The results of wear tests in laboratory and real environment will help to evaluate the embedding of such not metallic hard materials. The thermal stress of the hard materials is significantly lower with InduClad than with typical arc processes. It successfully avoided the floating of the relative light hard materials. We will present the first application examples of not metallic materials in abrasive wear protection technology.     

Untersuchungen zum Erosionsverschleiß an schweißtechnisch hergestellten Beschichtungen

Erosion resistance of hard‐facing deposits Erosive wear is inflicted by flying, bumping and furrowing particles inside the gaseous medium. Especially air vents – fan blades are the principal victims ‐ and conveying systems are attacked by solid particle impingement if fly ash, raw‐meal, cement or clinker are involved. High load of particles in combination with high circular velocities cause enormous loss of material on exposed components. Hard‐facing deposits as produced by flux‐cored arc and plasma trans‐arc welding in form of wear plates or local overlays at pertinent places are able to diminish this effect. Secure dimensioning of above mentioned systems during project engineering status only is hardly possible. So far solutions for wear protection are mainly based on time‐ and cost‐intensive field tests on the part of the manufacturer or user of affected plants and equipment. Within the framework of presented investigations experiences in laboratory testing of hard‐facing materials for attacked components are discussed. Wear tests on platings by practically relevant media give information about influencing factors as well as wear‐ and damage‐mechanism.     

Effect of load on tribofilms at the contact interface under dry sliding conditions at 500 °C

This paper presents a study of the effect of load on the retention of the tribofilms formed at the interface of a dry sliding contact between exhaust valve material, Nimonic alloy (N 80A) and valve‐seat material, ductile cast iron (GGG‐40), at a temperature of 500 °C. The role of tribofilms in influencing friction and wear behaviour at elevated temperature is highlighted. Reciprocating pin‐on‐disc experiments were conducted using a hemispherical shaped pin sliding against a flat disc at 20 Hz oscillating frequency, 2 mm stroke at loads of 20 N to 50 N. Low coefficient of friction, in the range of 0.13 to 0.15, was observed at loads up to 40 N whereas at a load of 50 N, the average coefficient of friction increased to 0.29. Optical and scanning electron micrographs with energy dispersive spectroscopy analysis indicate evidence of formation and retention of well compacted and strongly adhering tribofilms at loads up to 40 N. At 50 N, even though more abrasive wear is seen, initial deterioration and subsequent reforming of the tribofilms with increasing sliding time is observed. Overall, more wear was observed for the valve‐seat material as compared to the valve material. Raman spectroscopy primarily indicates the presence of hematite on the worn surfaces at loads of 20 N to 40 N, whereas magnetite presence is strongest at the highest load of 50 N. Increase in tribofilm hardness was observed with increase in contact load whereas the thickness of the tribofilm was not significantly affected by the contact load.     

Optimum selection of novel developed implant material using hybrid entropy‐PROMETHEE approach

Optimum selection of appropriate biomaterial with unlike properties for the femoral head material is one of the toughest tasks. Therefore, in this article, a series of implant materials for the femoral head by vacuum casting induction furnace containing cobalt‐30chromium (Co‐30Cr) as a base material and three alloying elements (i. e. molybdenum, nickel and tungsten) were developed and evaluated for physical, mechanical and tribological properties. Density, hardness, compressive strength, coefficient of friction and volumetric wear were considered as material selection criterions. The weight of each criterion has been determined by entropy method, while the ranking of the alternatives has been carried out by the preference ranking organization method for enrichment evaluations (PROMETHEE) method. From this ranking results, it is found that the cobalt‐30chromium‐4molybdenum‐1nickel‐2tungsten (Co‐30Cr‐4Mo‐1Ni‐2W) material at given parameters is the best implant material for the femoral head component of hip joint replacement.     

Eigenschaften und Anwendungen von Chemisch Nickel‐Dispersionsschichten

Properties and applications of electroless nickel composite coatings This paper discusses the variety of composite electroless coatings used in different industrial applications. The inclusion of particulate matter within electroless nickel deposits can add entirely new properties to the plated layer. Composites with hard particles like diamond, silicon carbide and boron carbide provide greater wear resistance and the possibility for adjustable friction properties. Composite electroless nickel with diamond or ceramics has found wide applications in the textile, automotive and mechanical engineering industry. Friction joints in automotive engines constitute an important field of application for diamond coatings. Modern internal combustion engine designs require that the crankshaft and camshaft be fitted at a specific relative angle. In order to establish the correct angle during assembly and maintain it over the life of the engine, axial press‐fit joints in combination with centrally located retention bolts are employed. Failure of either the joints or the bolts can result in serious damage to the engine. The torque transfer ability of these engine components can be significantly increased by incorporating a friction foil that is diamond‐coated on both sides. Composite coatings with coarser diamond particles can be used for the coating of precision tools in the semiconductor industry. Enhanced lubricity can be achieved by incorporating solid lubricants in electroless nickel deposits. Composite coatings with PTFE or PFA offers non‐stick surfaces with antiadhesive properties and good resistance against adhesive wear. Because of the temperature and softness limitations these coatings are best suited for lower temperature and light loading applications. Electroless nickel boron nitride coatings can withstand temperatures up to 600 °C. This coating reduces coefficient of friction and wear in dynamic applications. A further application is the coating of molds for rubber and plastic components.     

Einsatz von Hartstoffbeschichtungen bei Spindellagern

Application of hard surface coatings for spindle bearings The demands on modern Machine Tools ascends continuously with the requirements of the production for high quality and short‐time processings. Particularly the increase of the processing‐ and removal times of the last years dues to higher loads of the main spindle bearing. The bearing as a central machine component characterises the performance of the Machine Tool for the cutting process and defines the reliability of the main spindle. The majority of the applicated spindle bearings are ball bearings. A large amount of the spindle fall‐outs is caused by a non adequate or defecitive lubrication and is effected by the tribological properties of the bearing elements. For the reduction of friction and wear nowadays several materials, coatings and lubrication additives are applied. Actual researches focus on the development of hard surface coatings (a‐C:H:W) with a nano structure for the rolling contact of ball bearings to increase their reliability. In this article the test of nano structured hard surface coating systems for the reduction of friction, warming and wear are presented. Thus the coating systems are verificated for the application in spindle bearings by pretesting. According to the evaluation the inner and outer raceway of standard‐hybrid bearings are coated and the adhesion in reference to rotational speed, resistance and wear performance at high acceleration is analysed. Concluding the emergency running properties at dry‐running condition is evaluated to identify the field of application for the coatings.