Modifizierung der Gasabgabe von Edelstahloberflächen durch Ionenimplantation

Several years ago there were established a new ion-implantation technique, the so called Plasma source ion-implantation. This technique was applied on stainless steel samples to implant ions of nitrogen or oxygen into the surface in a controlled manner and to create barrier layers of nitrides or oxides, respectively. With the help of surface-analytical methods it could be shown that oxygen or nitrogen were incorporated homogeneously in a certain depth region below the outermost surface. Some measurements of the outgassing behavior of these plasma treated surfaces will be shown. The results are discussed as originated from the surface modification by the plasma treatment and the creation of the implantation layer.     

Veränderung des elektrochemischen Korrosionsverhaltens und der mechanischen Eigenschaften von C/Al-Verbunden durch Faserbeschichtungen aus SiC und pyrolytischem Kohlenstoff

Changes of the electrochemical corrosion behavior and the mechanical properties of C/Al-composites due to SiC and pyrolytic carbon fiber coatings The following contribution describes the modification of the electrochemical and mechanical behavior of carbon fiber reinforced pure aluminum (C/Al-composite) due to two different fiber coatings. Tests include potentiodynamic corrosion tests, Transmission electron microscopy, bending tests and single fiber-“push in”-tests. The potentiodynamic corrosion tests were carried out in 3,5 wt.% NaCl solution. The results give evidence of a considerable decrease of the corrosion resistance of the C/Al-composites due to the application of the pyrolytic fiber coating. The SiC coating improves the corrosion resistance of the composite. However, the mechanical properties of the composites were harmed by the SiC coating. The pyrolytic carbon coating leads to a remarkable energy dissipation due to “stick-slip” effects on the interface under load. Consequently, the application of suitable multilayers of pyrolytic carbon and SiC fiber coatings could result in improved electrochemical and optimized mechanical properties of the C/Al-composite.     

Nanostrukturierung von Kupferoberflächen durch Sauerstoff‐induzierte Rekonstruktionen

Nanostructuring of Copper Surfaces by means of Oxygen induced Reconstructions For metal single crystals the topography of vicinal surfaces can be changed in a controlled fashion by means of oxygen adsorption. This self‐organized phenomenon will be demonstrated for several vicinal copper surfaces. For densely packed copper surfaces with terrace lengths of ≤ 1 nm oxygen adsorption causes a doubling of terrace length and step height, whereas an oxygen‐induced mesoscopic faceting into periodic nano‐stripes is observed for regular monoatomic stepped surfaces with longer terraces. The width of the resulting nano‐stripes depends on the orientation of the clean vicinal surfaces and values of 10 to 50 nm have been observed. The thermal stability of the surfaces is found to increase with the stripes width, some structures are stable for temperatures up to 800 K.     

Verringerung der Belagbildung durch beschichtete Oberflächen

Fouling on heat exchangers is a well known but unsolved problem in the area of heat transfer. This additional layer could be formed by crystallization, particles, biological systems or by chemical reaction. It was estimated that the costs due to fouling in industrialized countries are about 0.25 % of the GDP (6.2 bn. Euro for Germany, 2008). Due to the isolating effect of the fouling layer, the total heat transfer of the equipment is declined. To maximize the operation time between cleaning cycles of the heat exchanger and to minimize cleaning time, a defined change in the molecular interaction between fouling layer and heat transfer surface is required. PACVD (Plasma Assisted Chemical Vapor Deposition) coatings can realize this and have shown their potential to mitigate fouling. Especially modified DLC (Diamond Like Carbon) were investigated. The operation time of a heat exchanger in lab scale could be extended by the factor of 10 with a tailor made surface.     

Reibung und Verschleiß von Polymer-Verbundwerkstoffen

Friction and Wear of Polymer Composites Polymer composites are more and more used as structural components which are very often subjected to friction and wear loadings under use. This paper describes the principle microstructure in polymer composites and their friction and wear properties as a function of microstructural composition. Special attention is focussed on the behavior of these materials under sliding situations against steel and under severe abrasive loading (wear by rough abrasive paper). Models to describe the tribological properties of composites by modified rules of mixtures and/or by terms combining mechanical and microstructural parameters of the partners in contact are introduced.     

Klebflächenvorbehandlung von Aluminiumoberflächen mit Haftvermittler

Surface pretreatment for adhesive bonding of aluminum with adhesive mediator The influence of three steps pretreatment degreasing, blasting and primer and the two steps pretreatment degreasing and blasting on the adhesive behaviour of aluminum alloy AlMg4,5Mn0,5 were investigated. The investigations were preformed using two cold hardening two‐components epoxy adhesives, one hot hardening one‐component epoxy adhesive and one cold hardening two‐components polyurethane adhesive. The three steps pretreatment indicate that the adhesion bonding strength by epoxy adhesives are higher than that by two steps pretreatment. On the other hand, the adhesion bonding strength was similar by using polyurethane adhesive independence of the pretreatment method. Leaving out the pretreatment step degreasing after corund blasting caused by using, PU, EP 2 and EP 3 adhesives a significant decreasing of the bonding strength in comparison with the only degreased specimen. This degreasing process was used to remove the residual blasting medium from the aluminum surfaces after blasting. The topographical structure of the surfaces after corund blasting was covered by further pretreatment with primer as a consequence of higher primer viscosity, which causes a decreasing in the surface roughness. The chemical composition of pretreated surfaces by three steps was different from that by two steps.     

Funktionale Oberflächen auf Duplex‐Stahl durch Laserfeinbeschichten

Functional surfaces on duplex stainless steel by lasercladding The product‐lubricated axial and radial bearings installed in multistage high‐pressure pumps inevitably encounter severe mixed friction conditions as the pumps start and stop. This leads to extremely high tribological loads on the bearing components, compounded by the effects of a highly corrosive pumped fluid. The present paper describes a laser cladding process which produces near‐net‐shape coatings of new, highly corrosion and wear resistant functional layers which can be deposited directly on high‐alloy stainless steels without requiring additional buffer layers and without affecting the mechanical properties and corrosion resistance of the substrate. The results cover the solidification behaviour of the coatings as well as the microstructure resulting from various heat treatment conditions. In addition, the technological properties of the coatings and the resulting composites are discussed. The coating systems are tested as to their corrosion resistance and tribological characterization in a pump‐specific tribological system.     

Transparente und leitfähige Veredelung von Kunststoffoberflächen

Deposition Techniques for Transparent Conducting Thin‐Films on Glass and Polymer Substrates We report on thin films deposited at atmospheric pressures on glass and polymer substrates with various techniques. The introduced thin‐film materials show intrinsic properties being suitable for different applications while maintaining the principle properties of the substrates themselves (e. g. shape. rigidity/flexibility, transparency). With the main focus on optical and electronic applications the properties of the deposited films can be adjusted by the choice of coating material (e. g. metal oxide, CNT), the film's shape (compact, particulate) and the deposition process itself. We compare deposition and properties of different TCO‐materials with CNT‐based thin film techniques and demonstrate approaches for the integration of these processes in production lines.     

Werkstoffanstrengung bei Wälzbeanspruchung – Einfluß von Reibung und Eigenspannungen

Material Stressing under Rolling Contact – Influence of Friction and Residual Stresses Material stressing of parts in rolling contact is in the main made up by the normal load to be transmitted, by surface friction due to slippage of the body in rolling contact and by residual stresses. The effects of varying slippage rates are described as well as the additional influence of residual stresses on magnitude, position and direction of load. By the aid of mere mechanical reflections the formation of flat and steep White Bands can be interpreted which are observed in long-lived ball bearings subjected to high stresses. The report shows that residual stresses and friction must not be neglected when describing the material stressing by rolling contact. This especially applies to residual stresses originating from rolling contact.     

Klebflächenvorbehandlung von Aluminiumoberflächen mit SIP‐Haftvermittler

Surface pretreatment for adhesive bonding of aluminium with adhesive mediator SIP The present contribution describes the influence of different surface pretreatments including adhesive mediator SIP for adhesive bonding of aluminium alloy AlMg4,5Mn0,4. The investigations were performed using two cold hardening two‐components epoxy‐adhesives, one hot hardening one‐component epoxy‐adhesive and one cold hardening two‐components polyurethane‐adhesive. The adhesive bonds with epoxy‐adhesives show after three‐step pretreatment degreasing + corundblasting + SIP coating the highest adhesive strength values whereas adhesive bonds with polyurethane‐adhesive showed a decrease of bond strength as compared with the delivering surface condition.     

Mikrostrukturelle Veränderungen von Magnesium‐Druckgusslegierungen nach langzeitiger thermischer Beanspruchung

Microstructural Changes of Pressure Die Cast Magnesium Alloys after Long‐Term Thermic Loading The expansion of the application of pressure die cast magnesium alloys for automobiles requires the development of new alloys and the comprehensive assessment of available alloys on aggravated conditions, too. Such conditions are also given at higher temperatures, which can cause the creep of the material and lead to the component failure. Because the microstructural stability decisively depends on the thermic loading, this paper deals with the change of the microstructure and the hardness of the alloys AZ91, AM50 and AE42 after a long‐term annealing at 150 °C and 200 °C in comparison to the pressure die as‐cast condition. The results reveal clear differences of the microstructural stability of the alloys AZ91 and AM50 on the one hand and the alloy AE42 on the other hand. Due to the long‐term annealing at 150 °C the alloys AZ91 and AM50 show chiefly an intense precipitation of Mg₁₇Al₁₂ from the Al‐rich eutectic α‐phase. Furthermore at 200 °C, it is observed the coagulation and coarsening of these precipitates, too. The last appearances are connected with a weakening of the material. Regarding the alloy AE42, the changes of the precipitation state are not so intensely and do yet not lead to a microstructural weakening.     

Die thermische Stabilität von Eigenspannungen in kugelgestrahlten Oberflächen

Thermal Stability of Residual Stresses in Shot Peened Surfaces . In industry shop peening represents a well-known process to improve the fatigue properties of metallic components. However, the beneficial effect of the induced compressive residual stresses can be reduced if a component is subjected to higher temperatures during service. In this work the relief of the residual stresses as a function of time and temperature is calculated for a 12 %-chromium steel. Specifically, the results can be used for the prediction of the stress relief behaviour of gas turbine compressor blades. This model can also be applied to the determination of the mechanisms which are responsible for the residual stress relief. At temperatures above approximately 300 °C in this material the dominating mechanism is diffusion controlled creep whereas at lower temperatures the stress relief is caused by logarithmic creep.