Tribologisches Verhalten von Kunststoffen bei tiefen Temperaturen

Tribological Behaviour of Thermoplastics at low Temperatures The lubrication of sliding bearings for application to low temperatures is difficult, caused by the special failure after long standing of the most lubricants. An alternative is given by so-called „self-lubricated”︁ thermoplastic materials. Thermoplastic based composites with different filler materials have a good mechanical and thermal load capacity up to temperatures T = 200°C. The addition of sliding modifiers gives low friction coefficient and wear. Unknown is the behaviour of these materials at low temperatures. The aim of this work is to develope a test facility to estimation the tribological behaviour of materials at temperatures up to T = – 196°C and to investigate the application of different thermoplastic materials in friction with a steel of typ 100Cr6 as the counterbody under dry wear condition. Advanced thermoplastics, e.g. PPS, PAEK, PES or PI and PTFE with different fillers using for the investigations at temperatures T = − 40°C, room temperature and T = 160°C. The typical failure mechanism depending on the proof temperature are discussed.     

Latest progress on tribological properties of industrial materials

Wear is closely related to friction and lubrication; the study of these three subjects is known as tribology. In science and technology it is concerned with interacting surfaces in relative motion. Soft or hard film coating, alloying and composite structuring have all been developed to control wear and friction. This is achieved by improving materials and surfaces with some characteristics that improve resistance to friction and wear. In recent years, several new solid lubricant and modern lubrication concepts have been developed to achieve better lubricity and longer wear life in demanding tribological applications. Most of the traditional solid lubricants were prepared in the form of metal, ceramic and polymer–matrix composites. They have been used successfully in various engineering applications. Recent progress in thin-film deposition technologies has led to the synthesis of new generations of self-lubricating coatings with composite or multilayered architectures, by using multiplex surface treatments. In this study, typical wear behaviors of representative materials of metallic alloys, ceramics, polymeric materials, and composites are reviewed in relation to their friction behaviors. Additionally, modeling for the wear prediction is outlined.     

Lubricious zinc oxide films: synthesis, characterization and tribological behaviour

Solid lubricants that are effective over an extreme range of operating temperatures are necessary for the development of new generation high-performance gas turbine engines with increased propulsion capability. While oxides have the potential to perform as high-temperature lubricants, they typically have high friction and create abrasive wear debris at low temperature. The objective of this work was to create oxides that have good tribological properties at room temperature through control of microstructure and stoichiometry. Zinc oxide films were grown by pulsed-laser deposition. The stoichiometry and microstructure of the films were controlled by adjusting substrate temperature and oxygen partial pressure during pulsed-laser deposition. Chemistry and microstructure were probed using SEM, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Friction coefficients and wear life were measured using a ball-on-flat tribometer. The degree of similarity of the coatings to bulk ZnO was RT, vac<RT, O2<300°C, vac<300°C, O2. Coatings with oxygen deficiency and nanoscale structure have low friction (i.e. μ<0.2) and long wear lives (i.e., greater than 106 cycles) at room temperature. As the chemistry and crystal structure of a coating approaches that of bulk ZnO, its tribological properties degrade and can become load/speed sensitive. An important result of this study is that oxides can be made to provide good tribological properties at room temperature. Thus, there is significant potential to produce low-friction, low-wear oxide coatings for wide-temperature range applications by controlling nanostructure and oxygen vacancies. This revised version was published online in November 2006 with corrections to the Cover Date.     

Eine Cermet-Glasschmiermittelkombination für Reibpaarungen bei Arbeitstemperaturen von 650–1100°C

A cermet/lubricating glass-combination for friction pairs at working temperatures 650–1100°C The function and the efficency of technical plants are limited by the used materials and their behaviour under working conditions. At elevated temperatures, the corrosion and wear resistance and the thermal shock behaviour are as necessary as mechanical stability at high operating temperatures. Metals and ceramics often cannot meet the conditions. Dynamic applications may require lubricatings, metals surfaces may be too soft and not very oxidation-resistant. Metal-ceramic materials, -cerments-, use a combination of the properties of their microstructural parts. This paper shows a combination of a cermet and a lubricating glass with interesting aspects for high temperature operation.     

轮缘固体润滑剂对轮轨减摩及损伤性能影响

用MMS-2A滚动摩擦磨损试验机完成试验工作,对比干态和3种不同固体润滑剂作用工况,分析干态和3种不同固体润滑剂作用后的轮轨摩擦性能和固体润滑剂的有效作用时间,探究固体润滑剂对轮轨摩擦性能的影响;分析不同工况下轮轨表面磨损量和表面裂纹,同时对裂纹的长度、角度、深度进行统计,分析固体润滑剂作用对轮轨损伤性能影响。结果表明:固体润滑剂具备减摩润滑作用,其中1号效果最佳,将干态下的摩擦系数0.5降低到0.2左右;固体润滑剂通过降低接触界面的摩擦系数减小轮轨界面的切向摩擦力,降低轮轨表面的磨损量,其中固体润滑剂1降低车轮和钢轨的磨损量最大,分别降低95.3%和97.1%;固体润滑剂主要通过抑制疲劳裂纹的长度来抑制轮轨疲劳裂纹的生长和扩展,通过正应力挤压作用使轮轨表面疲劳裂纹开口紧闭,缓解裂纹根部分支现象,有效抑制轮轨疲劳裂纹生长与扩展行为.     

Minderung von Reibung und Verschleiß von Bauteilen aus Aluminium mit diamantähnlichen Kohlenstoffschichten (DLC)

Reduction of friction and wear for parts made of aluminium by diamond-like carbon coatings Reduction of friction and wear of machine parts and tools is usually achieved by separating the participating surfaces. This is predominantly done by liquid lubricants. Solid lubricant coatings replace them where hydrodynamic lubrication is not possible or not active. Among the hard and friction reducing layers diamond-like carbon films (DLC) have distinguished themselves as the most interesting representatives. They are deposited on metallic and ceramic parts in a glow discharge of a hydrocarbon gas at temperatures between 150 and 200 °C. Those low deposition temperatures, their very low dry sliding friction coefficient of 0.05 to 0.1, and an elastic recovery of 90 % differentiate them from PVD coatings to a high degree. DLC can also be deposited on light metals with thicknesses of more than 30 μm. For closed films an outstanding protection against corrosion is established. Machining and forming of light metals can be done without cooling lubricants.     

Friction and wear behavior of carbon fiber reinforced brake materials

A new composite brake material was fabricated with metallic powders, barium sulphate and modified phenolic resin as the matrix and carbon fiber as the reinforced material. The friction, wear and fade characteristics of this composite were determined using a D-MS friction material testing machine. The surface structure of carbon fiber reinforced friction materials was analyzed by scanning electronic microscopy (SEM). Glass fiberreinforced and asbestos fiber-reinforced composites with the same matrix were also fabricated for comparison. The carbon fiber-reinforced friction materials (CFRFM) shows lower wear rate than those of glass fiber- and asbestos fiber-reinforced composites in the temperature range of 100°C-300°C. It is interesting that the frictional coefficient of the carbon fiber-reinforced friction materials increases as frictional temperature increases from 100°C to 300°C, while the frictional coefficients of the other two composites decrease during the increasing temperatures. Based on the SEM observation, the wear mechanism of CFRFM at low temperatures included fiber thinning and pull-out. At high temperature, the phenolic matrix was degraded and more pull-out enhanced fiber was demonstrated. The properties of carbon fiber may be the main reason that the CFRFM possess excellent tribological performances.     

含硫镍基合金与YJ2硬质合金对偶的高温摩擦特征分析

本文研究了通过热压法制备得到的含硫镍基合金与YJ2硬质合金对偶的摩擦特征。结果表明：在高温摩擦过程中，材料中的硫化物共晶体是主要的润滑组元，摩擦面的温度对其润滑效果有较大的影响；材料与YJ2对偶时的摩擦系数随着温度变化有所不同，但是磨损率都随着温度升高而增大，其高温下磨损形式主要为磨粒磨损和氧化磨损；YJ2硬质合金表面生成的氧化物对材料减摩性能有很大影响。     

Partikel- und Faserverbundwerkstoffe für Flüssigkeitsfreie Lager

Composite materials including particles and fibers as oil-less bearing materials Oil-less bearing can be fabricated by polymers and metals including solid lubricants (up to 10 w %) like PTFE, MoS₂ or graphite. If it is necessary by application to incorporate a greater content of solid lubricants, the mechanical properties of the composite materials are too weak. The mechanical properties of bearing material increase, when high tensile strength fibers are incorporated. In the case of graphite fiberreinforced polymers wear rate as well as coefficient of friction decrease, while the ultimate flexural strength increase rapidly. In the case of metallic matrices containing graphite fibers or steel wires the ultimate strength increases (above all the combination white metal/steel wire) as well as the wear rate decreases.     

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.     

Coatings for wear and lubrication

In this paper we review the recent advances in the tribological uses of r.f.-sputtered and ion-plated films of solid film lubricants (laminar solids, soft metals, organic polymers) and wear-resistant refractory compounds (carbides, nitrides, silicides). The sputtering and ion-plating potentials and the corresponding coatings formed are evaluated relative to the friction coefficient, wear endurance life and mechanical properties. The tribological and mechanical properties of each kind of film are discussed in terms of film adherence, coherence, density, grain si morphology, internal stresses and thickness and substrate conditions such as temperature, topography, chemistry and d.c. biasing. The ion-plated metallic films in addition to improved tribological properties also have better mechanical properties such as tensile strength and fatigue life.     

Solid lubricants: a review

The fundamental mechanisms of solid lubrication are reviewed with examples from well-known solid lubricants like the transition metal dichalcogenides and diamond-like carbon families of coatings. Solid lubricants are applied either as surface coatings or as fillers in self-lubricating composites. Tribological (friction and wear) contacts with solid lubricant coatings typically result in transfer of a thin layer of material from the surface of the coating to the counterface, commonly known as a transfer film or tribofilm. The wear surfaces can exhibit different chemistry, microstructure, and crystallographic texture from those of the bulk coating due to surface chemical reactions with the surrounding environment. As a result, solid lubricant coatings that give extremely low friction and long wear life in one environment can fail to do so in a different environment. Most solid lubricants exhibit non-Amontonian friction behavior with friction coefficients decreasing with increasing contact stress. The main mechanism responsible for low friction is typically governed by interfacial sliding between the worn coating and the transfer film. Strategies are discussed for the design of novel coating architectures to adapt to varying environments.     

A study of the dry friction characteristics of some cermets at high sliding speeds

Summary Satisfactory performance of rotary seal materials demands not only a relatively low hardness and high resistance to heat, but also good antifriction properties; the latter are required to ensure that the blade tips and rotary seal rings can readily cut into the inserts at high sliding speeds without seizing.The results of our study of the qualitative and quantitative characteristics of dry friction of cermet sealing materials in a wide sliding speed range (10–100 m/sec) showed that high temperatures attained by the surface layers of specimens tested at high sliding speeds lead to substantial changes in structure and properties of these materials, and that oxide films formed under these conditions prevent the onset of seizing. Graphite and boron nitride used as solid lubricants in the cermet sealing materials S-120 and UMB-4s act as protective antifriction additives. At sliding speeds higher than 70 m/sec, however, at which high temperatures are generated by friction, graphite burns out; as a result, both the friction coefficients and the rate of wear of material S-120 increase.Boron nitride is a more chemically stable solid lubricant; as a result, both the friction coefficient of material UMB-4s over the entire sliding speed range investigated and its rate of wear at high sliding speeds are lower than those of material S-120.     

Tribological and protective coatings by chemical vapour deposition

When steel and nickel-based alloys are to be used as substrate materials for the chemical vapour deposition of hard wear-resistant and corrosion-protective coatings because of their high mechanical strength, the criteria for choosing the correct grade have to be established. In this paper we contribute towards this goal. We also discuss the friction and wear behaviour of a number of refractory coatings, such as TiC, TiN, SiC, Cr₇C₃, Fe_xB and Al₂O₃, under different environmental conditions.Some industrial tribological applications at moderately high temperatures (350°C in a helium atmosphere) or where the environment precludes the use of fluid lubricants are presented to illustrate the technical and economic feasibility and the usefulness of such coated machine elements and wear parts.Finally we deal with a very special application, the industrial exploitation of which is only just beginning: a multiple refractory compound coating to improve the protection of niobium tubes in the core of a nuclear reactor from damage due to metallurgical corrosion by liquid steel at high temperature (1600°C) which would result from accidental failure of a fuel pin.     

Crystal growth of alkaline earth fluorides in a reactive atmosphere: Part III

A comparison of CF₄ and C₂F₄ as agents of reactive atmosphere processing (RAP) in the crystal growth of alkaline-earth fluorides is given. At temperatures much below the melting point of these metal fluorides, C₂F₄ decomposes into CF₄. CF₄ converts H₂O to HF, but has a much slower action on the dry metal oxides at ?1000°C, and, therefore, it is preferred as a secondary RAP agent to the fast-acting HF.     

Preparation and high-temperature tribological properties of CrAlVYN-Ag nanocomposite coatings

CrAlVYN-Ag coatings were successfully deposited by introducing the elements of V and Ag into CrAlYN hard coatings. Their microstructure and mechanical property as a function of the annealing temperature were investigated from room temperature (RT) (～25°C) to 800°C. Besides, the worn surfaces were analyzed after combined effects of temperature and friction to figure out the wear mechanisms at different temperatures. The coatings exhibited special surface morphologies and Ag diffusion after annealing at different temperatures. In addition, the x-ray diffraction results showed that the coatings suffered obvious oxidation once the temperature exceeded 600°C; as a result of this, the coating hardness decreased sharply. The friction coefficients were relatively high during the tribological tests from RT to 400°C because the abrasive wear mechanisms played a dominant role. The lower friction coefficients obtained at 600 and 700°C were mainly due to the self-lubricating mechanisms. However, the coating exhibited higher friction coefficient at 800°C, which was mainly ascribed to the severe oxidation wear of the coating.     

Synthesis of Iron-Based Friction Material by in Situ Reactive Sintering from Vanadium-Bearing Titanomagnetite

Based on the thermodynamic analyses, an iron-based friction material has been prepared directly from the vanadium-bearing titanomagnetite concentrates by means of a prereduction process and a final sintering process. Thermodynamically, ferrous oxides, titanium oxides, and vanadium oxides in the vanadium-bearing titanomagnetite concentrates can be converted to metal iron, titanium carbide, and vanadium carbide, respectively, by carbon at 1300°C in a vacuum of 10 Pa. During the process of prereduction, the percentage of ferrous oxides reduced to metal iron is about 96%, the percentage of FeTiO₃ converted into TiC is about 75%, and the percentage of V₂O₅ converted into VC is about 94%. During the process of final sintering, the samples were sintered at 1000°C for 3 h. The density, compressive strength, and Brinell hardness of this iron-based friction material are 5.07 g · cm^?3, 154.82 MPa, and 64 HBW, respectively. Its porosity ratio is about 18%. The stable coefficient of friction between this iron-based friction material and GCr15 is about 0.57 and the corresponding wear rate is 1.0145 × 10^?7 cm³ · J^?1. Consequently, the two-stage process presented in this paper can not only utilize the vanadium-bearing titanomagnetite concentrates effectively, but also find an alternative method to produce iron-based friction material economically.     

Influence of grain size on wear behavior of SiC coating for carbon/carbon composites at elevated temperatures

To improve the wear performance of SiC coating for C/C composites at elevated temperatures, the grain was refined by adding small amounts of titanium, in the raw powders for preparing this coating. The related microstructure and mechanical characteristics were investigated by scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy and nano-indention. The results show that the grain size of SiC coating decreased from ∼30 μm to ∼5 μm due to the addition of grain refiner. TiC formed by reacting titanium with graphite, can act as perfect heterogeneous nucleus for the nucleation and growth of β-SiC. The wear resistance and fracture toughness of SiC coating was improved by grain refinement. However, the increasing interfaces increased the friction resistance and resulted in the high friction coefficient of fine-grained coating at room temperature. As the temperature rose, oxides layer formed on the surface of fine-grained coating, which can reduce the adhesive wear and decrease the friction coefficient. The fine-grained coating exhibited relative low friction coefficient of ∼0.41 owing to a compact silica film formed on the worn surface at 600 °C, and the wear was dominated by plastic deformation and shear of silica film. The wear of coarse-grained coating was controlled by the fracture of SiC at high temperature.     

无机粘结固体润滑膜的研究进展

无机粘结固体润滑膜能显著降低摩擦系数,降低高温磨损并提高传动效率.剖析了硅酸盐、硼酸盐、磷酸盐3类无机粘结剂的结构特点与综合性能,重点结合无缝钢管热轧分析了磷酸盐粘结固体润滑膜的研究进展,再进一步对比分析了从层状材料、氟化物、软金属和氧化物、无机含氧酸盐到自修复润滑添加剂等方面的减摩与自修复作用机理;最后展望了无机粘结...     

Friction and wear behaviour of ion beam modified ceramics

In the present stud, the sliding friction coefficients and wear rates of carbide, oxide, and nitride materials for potential use as sliding seals (ring/liner) Were measured under temperature, environmental, velocity, and loading conditions representative of a diesel engine. In addition, silicon nitride and partially stabilized zirconia discs were modified by ion mixing with TiNi, nickel, cobalt and chromium, and subsequently run against-carbide pins, with the objective of producing reduced friction via solid lubrication at elevated temperature, Unmodified ceramic sliding couples were characterized at al temperatures by friction coefficients of 0.24 and above. However, the coefficient at 800° C in an oxidizing environment was reduced to below 0.1, for certain material combinations, by the ion implantation of TiNi or cobalt. This beneficial effect was found to derive from lubricious titanium, nickel, and cobalt oxides.