Verschleiß und Verschleißprüfung

Wear and wear Testing. The following six different wear mechanisms are briefly discussed: adhesive wear, abrasive wear, fatique wear, mechano-chemical wear and thermal wear. As to wear testing it is concluded that for obtaining a priori information on materials, laboratory testing can be quite useful, provided that the environmental conditions that prevail in practice are successfully reproduced in the laboratory. Further, it is always advisable to include in a test programme some reference materials on which practical information is available.     

Erzeugung und Charakterisierung porenbehafteter Prüfkörper für Schwingprüfung und Gießsimulation

A large number of specimens has been created and investigated for fatigue tests and the numerical simulation of porosity formation in castings. The specimens are made out of the alloy AlSi7Mg0.3, the porosity has been characterized by means of computer tomography. The obtained results are put into relation with production conditions, with emphasis on melt hydrogen content. Form and amount of porosity is investigated in conjunction with melt hydrogen content and the transition between solidification and gas porosity is documented. The evolution of pores of different size is scrutinized in detail.     

Feinst‐ und Ultrafeinkornhartmetalle: Tendenzen und Anwendungen

Submicron‐ and Ultrafine‐Grained Hardmetals: Tendencies and Applications Submicron‐ and ultrafine‐grained hardmetals are WC‐Co alloys with average WC grain diameters of ≤ 0.8 μm and ≤ 0.5 μm, respectively. The variation of grain size towards finer‐grain carbides has the advantage that both hardness and transverse rupture strength increase as grain size decreases. This combination of properties, which contrasts with the well‐known counter‐running relationship between hardness and transverse rupture strength found in conventional hardmetals, opens up a wide area of application for submicron and ultrafine grained hardmetals. Since their introduction, these hardmetals have firmly established themselves in metalcutting operations, predominantly in the areas of milling and drilling and to a lesser extent in turning and broaching. Submicron‐ and ultrafine‐grained hardmetals, particularly in combination with suitable coatings, are gaining increasingly in importance in the machining of highly heat‐treated and abrasive work materials.     

Ermüdungsverhalten und Dauerfestigkeit von Graphit und Aluminium – infiltriertem Graphit

Fatigue behaviour and endurance limit of graphite and of aluminium‐infiltrated graphite Fatigue properties of polycrystalline, isotropic graphite FU2590 and of FU2590 infiltrated with AlSi7Mg (FU2590/AlSi7Mg) were investigated in reversed bending tests at 25 Hz at numbers of cycles below 10⁷ and in tension‐compression tests at 20 kHz below 10⁹ cycles. The open porosity of Graphite (10‐11 Vol.‐%) was infiltrated with the aluminium alloy using the squeeze casting infiltration method, which led to an increase of the bending strength by 50 %, increase of tensile strength by 30 % and increase of stiffness by 15 %. Fully reversed tension‐compression loading of FU2590 delivers a mean endurance limit at 10⁹ cycles at the normalized maximum stresses (i.e. maximum tension stress of a cycle divided by the static strength) of 0,65±0,03. Mean numbers of cycles to failure of 10⁴ were found in fully reversed bending tests at the normalized maximum stress of 0,78. The infiltrated material shows approximately 30 % higher cyclic strength in reversed bending tests, and the mean endurance limit under tension compression loading increases by 15 %. The increased endurance limit of the infiltrated material is caused by the increased stiffness. The increased toughness of graphite due to the infiltration with aluminium is of additional beneficial influence at the higher cyclic stresses investigated in reversed bending tests and in static tests.     

Wechselverformung und Gefügeänderungen von Ck 15 und Ck 45

Microstructural Changes and Cyclic Deformation The crack initiation starts due to weakening and strengthening process during rotating bending. However a smaller plastic deformation amplitude is noticed at the same nominal stress compared to tension-compression stressed specimens. This results in a higher fatigue life. The different cyclic deformation behaviour was proofed by SEM (rotating bending specimens showed a lower slip line density compared to tension-compression specimens at the same nominal stress) and TEM investigations (the rotating bending specimens showed a smaller dislocation density at the same nominal stress). Furthermore it is showed, a correlation of cyclic stress strain data σ(ε_pls) between tension-compression and rotating bending specimens exists. This is also valid for the Manson-Coffin-relationship. the relation between lg ε_pls and lg N_B depends on the material (Ck 15, Ck 45) but not on the state of stress.     

Verschleißanalyse gewalzter und geschliffener Eisenbasislegierungsschichten mit und ohne Hartstoffverstärkung

In this research work the wear behavior of thermal sprayed wear resistant coatings, which are finished by incremental roller burnishing and by grinding in order to smooth the surface, are analyzed by means of the Pin‐on‐Disc test. Two different arc sprayed coatings WSC‐FeCSiMn and FeCrBSiMn are compared to each other. At first the microstructure of the smoothed coatings were characterized by investigation of the topography and morphology. After that the wear behavior was analyzed with two different counterparts made of stainless steel and ceramic. In order to determine the different wear mechanisms the wear traces have been investigated by scanning electron microscope.     

Kunststoffoptiken mit Antireflex‐ und Antibeschlageigenschaften durch Plasmaätzen und Beschichtung

Plastic optics exhibiting anti‐reflection and anti‐fogging properties produced by plasma etching and coating Plasma treatments are capable to generate antireflective surface structures on various polymers. On PMMA a self organized surface with nep‐like bumps exhibits excellent optical properties. Many other materials like polycarbonate, zeonex and lacquers can be etched after depositing a very thin initial layer to form a more holey structure. These surfaces attain high transmission values too and can be better stabilized by coatings than the nep‐ structure on PMMA. Interesting for practical applications are hydrophilic top‐layers to provide anti‐fogging properties in combination with improved transmission.     

Wälzverschleiß und -ermüdung von Bauteilen und Maßnahmen zu ihrer Einschränkung

Wear and Fatigue at Rolling contacts and Counter Measures Machine parts subjected to rolling contact fatigue, i.e. gears or rolling element bearings, are exposed to a very particular stressing condition. No comparable condition will occur for other technical applications. These typical conditions and their effects on the material behaviour are described comprehensively. An introductional overview for this are of technical knowledge is given, in particular for engineers not so much experienced with respect to this matter. The most important phenomena influencing the behaviour of parts subjected to rolling contact fatigue are presented as well as the physics of damage initiation and the appearance of damaged parts. It is demonstrated exemplarily, how the analysis of the damaging processes can be used to take counter measures. The referencing to the public literature has been done in a way to enable the reader to easily find material for a further improvement of his knowledge for particular items.     

Verschleiß von Maschinen und Werkzeugen beim Verarbeiten von verstärkten und gefüllten Kunststoffen

Wear of Processing Equipment and Moulds by Filled and Reinforced Plastics The introduction of filled and reinforced plastics into the market increased the problem of wear during processing. It is estimated that in Germany wear based losses are up to 500 Millions DM per annum. Special test methods have been developed for systematic analysis of wear phaenomena. A considerable progress has been achieved in solving these problems in close contact to the concerning industry.     

Oberflächen‐ und Dünnschichtanalytik – unverzichtbares Werkzeug für Schichtentwicklung und ‐produktion

Surface and thin film analysis – indispensable tool for coating development and ‐production Development and production of thin films for functional coating on special materials is unalterable combined with a permanent quality control and therefore use of sophisticated analysis and measurement techniques. The field of interest is belonging to all steps of the production chain, starting with the characterization of the substrate surface (e. g. glass, plastics), followed by polishing and cleaning processes up to depth profiling of complex multilayers. The typical analyses are focused onto topographical and chemical features and their influence onto the product functionality. The use of surface and thin film analytics for problem oriented characterization is demonstrated by a few examples, which deal with surface roughness, contamination, impurities and dopand profiles as well as composition variations in the surface near region.     

Die Faser- und Fadenverstärkung von plastischen und spröden Matrixmaterialien

Fibre- and Filament-Reinforcement of Plastic and Brittle Matrix Materials The tensile strength of a fibre-reinforced material depends on the stress-strain behaviour of the two components and on the volume percentage, the orientation and the geometry of the fibres. For production and application of the composite material at elevated temperatures the chemical reactions between fibre and matrix are of critical importance. It may be necessary to incorporate an intermediate layer in order to inhibit an excessively strong reaction or to increase the bond strength. Feasible fibre-reinforced composites with metallic matrices are discussed. Nonmetallic inorganic materials are rather difficult to reinforce because of their brittle fracture properties. Development trends in the field of fibrereinforced materials are outlined.     

Verschleiß und Verschleißschutz beim Spritzgießen

Wear and Wear Protection for Injection Moulding Increased power installations at injection moulding machines for higher polymer output rates require improved wear protection measures since the so called ?standard steels”? cannot cope with these demands. This publication describes the adhesive, abrasive and corrosive wear phenomena which are taking place in plasticating units of injection moulding machines as well as the causing factors and resulting effects by means of examples. The influence of different polymers and additives on the service life of the machinery components is also being considered. Finally the article presents solutions to achieve an effective reduction of wear by processing and design related measures, suitable metal surface treatment and adequate material selection for the plasticating unit.