Zusammenhänge zwischen Temperaturabhängigkeit des Spannungsintensitätsfaktors und dem Verschleiß

Relationships between thermal variability of the critical stress intensity factor and wear. The aim of these investigations was to establish to what extent relationships exist between the critical stress intensity factor and the wear resistance of very hard, refractory materials, in order to obtain a further value to characterize the technological behaviour of these materials. Investigations showed that such relationships exist when wear occurs with a slight rise in temperature within the material. It was also found that at higher temperatures, wear was conditioned by plastic deformations in the thinner surface layers and by the influence of the gaseous environment.     

Mikrostruktur‐Untersuchungen zum Schwingungsverschleißverhalten von Nickelkomposit‐ und Ni‐P‐Schichten

Microstructural and oscillating sliding wear studies of nickel composites and electroless Ni‐P layers In many industrial applications, oscillating sliding wear leads to serious damage of construction components. To avoid this, different layers of electroplated nickel and nickel composites as well as chemically deposited nickel phosphorus layers are used and/or tested. The performance of these layers under oscillating sliding wear was characterized. Additionally microstructure characterisations took place regarding grain size, particle content and distribution as well as concerning crystallization and development of tetragonal phase nickel phosphide. These results correlate well with the Martens hardness of the layers and contribute to understand the oscillating sliding wear characteristics of the examined layers. Heat treated Ni‐P layers achieve twice the hardness of nickel dispersion layers; however, fail under oscillating sliding stress by embrittlement, cracking and debonding. On the other hand dispersion‐hardening nano composites with TiO₂ clearly exhibit a more favourable tribological behaviour. A solid content of approx. 3 vol‐% leads to dispersion and fine grain hardening effects, which cause good protection against oscillating sliding wear; thereby the Ni‐matrix remains ductile. The incorporation of very hard particles (SiC) intensifies the oscillating sliding wear process due to the abrasive effect of the particles.     

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.     

Verschleißverhalten ledeburitischer Chromstähle mit Niob und Titan

Wear Behavior of Ledeburitic Cr-Steels with Niobium and Titanium By addition of niobium, titanium, titanium and carbon to a steel with 2% C and 12% Cr alloys with MC-Carbide content of 1; 2,5 or 5 vol.% were produced. The wear behavior of these alloys was investigated in comparison to common ledeburitic Cr-steels by means of a slow turn-test and the pin-on-disc method. The influence of carbides (amount, hardness and distribution) is described as well as a change in the matrix, caused by varying austenitizing and tempering temperature, Except for the alloys with 2,5 and 5 vol.% TiC and an alloy with 2,5 vol.% NbC at high matrix hardness, which show increased wear as compared to the ledeburitic Cr-steels, the wear rate is lowered by addition of MC-carbides. In the pin-on -disc test the wear rate is more significantly lowered by increasing the content of ratained austenite than by carbides.     

Entwicklung und Verschleißverhalten von Si3N4-Schneidkeramik

Development and wear behaviour of silicon nitride ceramic Cutting tools based on silicon nitride ceramic have been employed successfully in industrial ranges of application especially in cutting of grey cast iron. Nevertheless their availability is still limited due to various reasons, depending on the specific material properties. In order to improve the wear behaviour and the reliability of these tools a new silicon nitride ceramic matrix, bonded with grains of carbides, was developed. The paper presents results obtained during investigations on material specific wear mechanisms in face milling and turning. The responsible wear mechanism in turning are the high tool temperatures. They leads to a softening of the grain boundary phase so that the Si₃N₄-grains can be removed by the chip flow. The wear in milling is due to the high mechanical load accompanied with the frequency in period of cutting     

Zum Korrosions‐ und Verschleißverhalten von Nickeldispersionsschichten mit Nanopartikeln

Corrosion and Wear Behaviour of Nickel Dispersion Coatings with Nano Particles The present study describes the results of the electrochemical deposition of Nickel dispersion coatings from a Watts electrolyte with nano‐scaled particles. Subsequently, the incorporated particles lead to different microstructures and have impact on the mechanical properties. The corrosion and wear behaviour of these layers are of high interest regarding their applications. By means of potentiodynamic measurements and optical characterisation, the corrosion behaviour can by evaluated in correlation to the applied particles and additives. Unfortunately, an improvement of corrosion protection could not be measured. From investigations by means of oscillation tribometer, it can be shown that the incorporated particles improve the wear behaviour.     

Untersuchungen zu Zusammenhängen zwischen Schichtmorphologie und Herstellungsbedingungen an amorphen Siliziumnitridschichten

Electron microscopic investigations of magnetron sputtered amorphous SiN_x-coatings showed, that morphology changes with variation of working gas pressure and substrate position corresponding to the Structure Zone Model by Thornton. Increasing working gas pressure and displacement of substrate to larger radial distances influence columnar structures. Energy of particles and adatom mobility decrease with increasing pressure. In positions far from the centre of deposition there are more particles with oblique incidence. This leads to a shadowing mechanism. Columnar diameter increases and packing density decreases. The influence of working gas pressure and angle of incidence bears also an effect on the behaviour of mechanical stress. Coatings with coarse columnar structures have lower mechanical stress than coatings with fine columnar structures.     

Gefüge und Anlaßverhalten von Weißen Bändern

Structure and Annealing Behaviour of White Etching Areas Due to a high number of revolutions combined with high load beneath the surface of the rings of roller bearings so called white etching areas will accure in a distance of about 10 μm to 250 μm under the race way. Two different kinds of WEA's were observed: the 30° WEA's and the 80° WEA's were built up depending on the direction of the stresses beneath the Hertzian Contact region. To investigate the structure and the annealing behaviour of the WEA's, influenced by three different heat treatments, the inner ring of a ball bearing was used for preparation of the section samples. It was seen that a special temperature must be exceeded to introduce a significant microstructural change in the area of the WEA's. The measurement of the microhardness showed that the hardness decreases in the region of the WEA's, but that the adjacent areas posess a higher microhardness. To see the different behaviour of thermal reaction of a near surface sample with 15–20 Vol% of WEA's and a core sample, a thermoanalytical test was made which showed that the surface-sample had an exotherm behaviour, in relation to the core-sample, because it posessed a higher energetic level.     

Tribomechanische und -chemische Vorgänge an dem Wälzlagerstahl 100 Cr 6

Tribological Processes of the Ball Bearing Steel 100 Cr 6 . Tribomechanical and tribochemical processes of the ball bearing steel 100 Cr 6 were investigated under the influence of ultra high vacuum and different gases by the pin/ring method. The conditions for adhesive wear indicated by prow formation were optimal in ultra high vacuum. Pressures of oxygen, nitrogen and air greater than 10^?6 Pa increase the lubrication by formation of thin films, measured by ellipsometry. Increasing nitrogen pressure produces a surface hardening, which can be observed by nitrided wear particles. The presence of pure oxygen creates permanently oxide films with a thickness of 10 nm. This causes abrasive wear.     

Untersuchung der Reaktionsvorgänge zwischen gasförmigen und festen Metallen

Reaction of gaseous with solid metals . The reaction of gaseous zinc and cadmium with solid copper, silver, palladium and palladium silver alloys were investigated at various temperatures. Besides the cleanliness of the metal surfaces various other factors influence the zink tak up e. g. the shape of the surface. More than up to now it has to be kept in mind, that the zinc atoms spread as directed atomic beams. This results in possibilities of influencing the zinz up take.     

Verschleißprüfung und Verschleißverhalten von Hartmetallen

Wear testing and wear behaviour of cemented carbides Wear resistance is not a mater constant but a quantity of a system. For the judgement of a case of wear or for the choice of the suitable grade of cemented carbide it is necessary to investigate exactly the limiting conditions and the appearance of wear. The wear test can only be considered with exactly defined limiting conditions and only be compared with application of similar limiting conditions.     

Betrachtungen über mikrobiell induzierte Korrosionsvorgänge und deren biologischen Hintergrund

Studies on events of microbially induced corrosion and their biological background On a real cooling water system, damaged by microbiallyinduced corrosion (MIC), the brown layer found in the tubes has been examined for aerobic and anaerobic backteria, which belong to different metabolic groups. With regard to the low input of organic substrates the tubes for cooling water represent a lean location. Instead, several populations of aerobic, fermenting denitrifying and anaerobic bacteria develop under these conditions, situated on the tube' surface in the biofilm. On the basis of their metabolic activities the microbes contribute to those chemical reactions that cause the calssical types of corrosion. At the moment it is impossible to determine the magnitude of the microbial influence upon corrosion because thepopulation densities are still unknown. This essay offers a first glance at a complex system of inorganic elements, organic substrates and living organisms interacting in the biofilm.