Reaktive Nanometer‐Multischichten als maßgeschneiderte Wärmequellen beim Fügen

Reactive nanometer multilayers as tailored heat sources for joining The use of traditional joining techniques like soldering or brazing for heat sensitive microstructures often results in damaging or stress induced deformation of the components. Therefore a technology would be desirable, where heat is produced locally and only for a short time. A very promising approach is the application of socalled reactive nanometer multilayers. Reactive nanometer multilayers consist of several hundreds or a few thousands of alternating layers wi^th thicknesses in the nanometer range that can exothermic react wi^th each other. After a local activation of the chemical reaction by an electrical spark or a laser pulse, a self‐sustaining reaction starts, which propagates parallel to the multilayer surface resulting in a stable intermetallic single layer. The peak temperature of the reaction can be above 1000 8C, but the maximum temperature is only reached for several ten milliseconds. Therefore, the heat remains localized in the vicinity of the solder layers surrounding the reactive multilayer. During the entire process the components to be joined exhibit temperatures close to room temperature. We will show new results concerning the fabrication of reactive nanometer multilayers by magnetron and ion beam sputter deposition and the fabrication of free standing nanometer multilayers.     

Plasmapolymerschichten als Basis für maßgeschneiderte funktionale Oberflächen

Plasmapolymer coatings for tailor‐made functional surfaces The tailoring of surface properties via polymer coatings is currently a strongly pursued topic in various fields ranging from microsystem technology to bioanalytics. A precise tuning of surface properties, however, is only possible if chemically well‐defined processes are used that usually require reactive surface moieties to which molecules can be coupled. In this contribution we summarize studies that aimed at the modification of inert surfaces. For this purpose reactive groups at the surfaces are generated by plasma polymerisation of allyl amine which results in layers that contain amino groups. Initiator molecules for free radical polymerization processes are then coupled to these amino groups resulting in surfaces from which polymers can then be grown via surface‐initiated polymerization. Using these processes, polymer monolayers with very different properties can be generated by simply using different monomers.     

Zum Einfluss der Topographie der Stahloberfläche auf Fehler beim Stückgut‐Feuerverzinken

About the Influence of the Topography of the Steel Surface on Faults during Hot Galvanizing of Part Loads The topography of the steel surface can influence the formation of layers during hot galvanizing in many ways. Information is given on galvanizing faults caused by impressions in the steel surface (rolling and drawing ridges). Flux remainders accumulated in these impressions can be encapsulated in the zinc coating during hot galvanizing. This leads to cavities and pores in the coating or to sponge‐like zinc raisings at its surface. The flux remainders from the zinc coating can boil during powder coating and lead to blisters and pimple‐like rises in the coating. Therefore, steel surfaces designed for galvanizing should be even or only have flat impressions.     

Veränderung von Stahloberflächen durch Reibung

Steel Surfaces after Fricton Processes. Steel surfaces which have been treated by friction under different conditions are investigated by scanning-electron-microscopy. The well-Known differences in the treatment by either reciprocating or continuous sliding may be separated in pictures of high magnification very accurately. Liquid lubricants during boundary lubrication from layers of certain solidity on the surfaces. The addition of antiwear-additives gives a better adhesion of the layers on the substrate. The behaviour of additives containing phosphorus are investigated thoroughly and compared with competing results given in the literature. It is stated by magnified surface pictures that the original conditions of the surfaces have minor influence on the wear process.     

Gezieltes Beizen von Apparaten aus chemisch beständigen Stählen

Controlled Pickling of Apparatus made of Chemical-Resistant Steels Examples of material failure and corrosion trials are used to show that the chemical resistance of austenitic steel depends in many ways on the surface condition. Pickling is the best method for removing layers of oxide in preparation for passivation. Internal tensile stresses which are created near the surface by mechanical working, e.g. by turning, drilling and grinding, can assume higher values than those caused by shaping and welding. As a result stress corrosion cracking often occurs only in the region where the surface has been worked. Because the stresses responsible for this phenomenon rapidly fall off below the surface, it is usually possible to reduce them by pickling to the point at which damage of this kind is prevented. The amount of material which must be removed by pickling is determined by trials and pickling must be controlled accordingly.     

Mikrowellen‐PECVD für kontinuierliche Großflächenbeschichtung bei Atmosphärendruck

Microwave PECVD for continuous wide area coating at atmospheric pressure Plasma processes are applied for a variety of surface modifications. Examples are coatings to achieve an improved corrosion and scratch protection, or surface cleaning. Normally, these processes are vacuum based and therefore suitable to only a limited extend for large area industrial applications. By use of atmospheric pressure plasma technology integration in continuously working manufacturing lines is advantageously combined with lower costs and higher throughput. Microwave plasma sources present powerful modules for plasma enhanced chemical vapour deposition at atmospheric pressure. At Fraunhofer IWS processes and equipment as well as application specific materials are developed. The coatings are suitable for scratch resistant surfaces, barrier and corrosion protective layers or anti‐reflex layers on solar cells. The film properties achieved are comparable with those produced by low pressure processes.     

Der Nachweis dünner Fremdschichten auf Kontaktoberflächen

The detection of thin contaminated layers on contact surfaces . Today electrical contacts must satisfy requirements which are growing steadily. The detection of very thin contaminated layers at contact surfaces therefore becomes very important. Clad gold contacts were contaminated with very small amounts of Zink. Contact resistance measurements and surface analysis measurements by AES and SIMS were shown to be adequate for the detection of this surface contamination.     

Randzoneneigenschaften und Oberflächenausbildung geschliffener Aluminiumoxidkeramik

Surface Integrity and Surface Structure of Ground Alumina Ceramic During the sinteoring process ceramics undergo a volumetric shrinkage and thus are far from meeting high demands on their form and size accuracy. To meet these demands in most cases finishing processes with diamonds are necessary. The machining processes influence the surface topography as well as the surface integrity of the components. The surface integrity of machined ceramics can be characterised by cracks and residual stresses. In order to improve the knowledge about surface layers of machined ceramics this paper describes the influence of the grinding process on surface structure and surface integrity. The influence of the setting quantities of the process on crack population and residual stresses and stress gradients will be discussed.     

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.     

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.     

Laserakustik für Schicht‐ und Oberflächenprüfung

Laser‐acoustics for Testing Coatings and Material Surfaces A laser‐acoustic test method is presented, which can be used for the non‐destructive characterization of coatings and material surfaces. The method measures the dispersion of surface acoustic waves induced by short laser pulses. The technique is based on the fact that the propagation velocity of the wave depends on the frequency in coated and surface modified materials. Measuring the dispersion of the surface acoustic wave enables to determine important properties of the material surface. Three examples demonstrate that the laser‐acoustic method can solve very different problems of surface engineering. The wear resistance of diamond‐like carbon film with a thickness of few nano‐meters was evaluated. The elastic modulus of thermally sprayed coatings which are typically some hundred micro‐meters thick was measured, which allows to conclude on the defect structure of the coatings. The depth of sub‐surface damage layers in semi‐conductor materials was determined, which are created when the wafer is sliced from the ingot.     

Elektrisch leitfähige kohlenstofffaserverstärkte Kunststoffe (CFK) mit freiliegender Funktionsschicht

Efficient lightweight requires intelligent materials that meet versatile functions. One approach is to extend the range of properties of carbon‐fiber‐reinforced plastics (CFRP) by plating the fiber component. Functions such as thermal and electrical conductivity, contactability, solderability, and adhesion promoting are integrated on this road. When processing the metallized carbon fibers to carbon‐fiber‐reinforced plastics the functional layer is covered by the matrix polymer. Thus, it is no longer accessible for further proceeding. In this work, different strategies for the production of carbon‐fiber‐reinforced plastics with accessible functional layers are analyzed. Thereby, selective uncovering of the functional layer as well as proceeding the carbon‐fiber‐reinforced plastics and metal‐layers without damages are important criteria. An evaluation of the processes was carried out using microstructural investigations and adhesive tensile testing. Correlations between electrical conductivity measurements, wetting and joining experiments, surface machining and solderability can be derived.     

Niedrigemittierende Außenoberflächen bei Wärmedämmverbundsystemen – ein Studie zur Vermeidung von Algenwuchs

Algae growth on the outside surface of thermal insulating composite systems (TICS) occurs because of long‐lasting wetting. The present techniques for its avoidance are without long‐term effect. Especially, dew and frost are an essential reason for its occurrence because of the highly thermal insulation of the TICSs. In the following report, it will be investigated by an algorithm on the basis of a worst case scenario for outside condensation whether outside condensation on TICSs can be counteracted by a low‐emissivity outside surface as it is well‐proven on highly insulating window glazing. The calculations showed that outside condensation on TICSs with heat transfer coefficients (U) values from 0.1 to 0.2 W/(m² K) cannot be avoided theoretically by thermal emissivity values ε in the range of 0.05 till 0.1. However, because the most critical scenario conditions for outside condensation are very stringent and, in addition, the calculations have shown that outside condensation is only possible for relative outdoor humidity rH_o ≥ 95%, it can be deduced that the occurrence of outside condensation will be very improbably in praxis for TICSs with U values from 0.1 to 0.2 W/(m² K) and ε values from 0.05 to 0.1. A weathering and soiling resistant surface with ε ≤ 0.1 can be realized by aluminum which may be additionally passivated by a titanium dioxide coating. Because of the hydrophilic property, this coating shows also self‐cleaning effect and quickly drying of the surface after rain. The latter may counteract algae growth, too.     

Berührungslose Prüfung von Kunststoffen mittels photothermischer Wärmewellenanalyse

Remote Testing of Polymers with Photothermal Analysis of Thermal Waves After an introduction to thermal waves a comparison is made of photoacoustic detection methods (gas cell, piezoceramic) and photothermal detection arrangements (front surface and rear surface methods). Previously only photoacoustic methods have been applied to polymer related problems, while the advantages of photothermal measurements – remote and nondestructive evaluation – have been demonstrated on metals. The experimental part of this paper presents first steps to apply photothermal analysis of thermal waves to some problems of polymers: thickness measurement of thin layers; on-surface and subsurface defects; delamination of bonding and coating curing reactions; glass fibre content; orientation of fibres and molecules; aging processes. The present results indicate that the method can be used for nondestructive remote quality assurance of thin layers and foils. Further development is required to apply the method to nondestructive testing of thick walled components.     

Röntgendiagnostik plasma‐gestützt abgeschiedener dünner Schichten

X‐ray diagnostics of plasma deposited thin layers Grazing incidence x‐ray diffractometry (GIXD) and x‐ray reflectometry (XR) have been introduced as well suited tools for investigations of plasma deposited thin layers. They are non‐destructive techniques, therefore a sample can be reused and measured with other techniques. A combination of GIXD and XR can give a range of interesting information about chemical, physical and crystallographic properties of thin films. Conclusions can be drawn how plasma deposition techniques and plasma parameters influence the film growth. In three examples we present the analysis of phase and chemical composition, defect structure and measurements of kinetic process parameters.     

Randschichtzustände von normalisiertem und vergütetem 42 CrMo 4 nach konsekutiven Kugelstrahl- und Festwalzbehandlungen

Near surface materials states of normalized as well as quenched and tempered SAE 4140 after consecutive shot peening and rolling treatments The near surface states of normalized as well as quenched and tempered SAE 4140 after consecutive shot peening and rolling treatments are presented and discussed. Especially in the normalized state separately shot peened or rolled specimens reveal characteristic differences in the near surface dislocation structures and in the thickness of the subsurface areas influenced by the mechanical treatments. In case of the consecutive application of shot peening and rolling, a sequence effect occurs in such a way that the finally applied surface treatment determines the microstructure of the very surface and the subsurface materials layers.     

Werkstoffzuverlässigkeit in der Tribologie

The Reliability of Materials in Tribology. The reliability of materials is, in general, reduced by lack of knowledge or the disregard of reaction mechanisms, by the disturbance of chemical or physical conditions of equilibrium and by changes in systems (e. g. combinations of materials, manufacturing processes, interaction with the environment etc.) entailing serious consequences. In the field of tribology, the following examples may be encountered:

• – Reaction mechanisms: Irreversible single threshold value: Transition from a metastable to a stable system; Crystallisation of synthetic materials; Abrasion phenomena with coating layers. Reversible threshold value: Volume change due to changes in physical state; Reversible structural transition. Irreversible cumulative threshold value: Influence of light on the resinification of lubricants; Crack development in the case of fatigue failures; Structurally unstable surface layers; Structural ageing phenomena.
• – Equilibrium: Wear/repolishing equilibrium; Tribological equilibrium of the surface structure; Compatibility of bearing materials; Consumption of additives in lubricating oil; Tribology and corrosion.
• – Interactions and system changes: General influence of basic materials; Interactions and catalysis; Evaporation of synthetic materials; Cleaning systems; Vibration.

     

Struktur und Eigenschaften nichtrostender Stähle nach einer Plasmaimmersionsionenimplantation und einer Plasmanitrierung

Structure and properties of stainless steels after plasma immersion ion implantation and plasma nitriding Stainless steels can be nitrided at temperatures ≤ 400 °C to increase their hardness and wear resistance without a decreasing of their excellent corrosion resistance. Structure and properties of the surface layers produced by plasma nitriding and plasma immersion ion implantation in this temperature range were tested. There are negligible differences in the structure of the produced surface layers in spite of different interaction principles of the used technologies. However there are clear differences between the case of different steels. The case of ferritic chromium steels mainly consists of ε-nitride. Whereas the cases of austenitic and ferritic austenitic steels are characterized by expanded austenite. The corrosion resistance of the steels is reduced by nitriding only, if evident CrN-formation occurs.     

Kommunikationsoberfläche Membran‐ Vorbild für moderne Nanoanalytik

A central event in the life of a cellular system is the interaction between the exterior and the interior compartments. Biochemical signals arrive at the cellular surface, bind to their membrane bound receptor followed by a conformational change triggering the release of an internal chemical or electrical signal.This basic principle is followed by all our perceptive abilities like sense of smell or taste, but also by different signal transduction pathways involved in nerve conductivity, vision, sense of touch or hearing. To follow and mimic this principle of parallel registration is one of the aims of modern nanobiotechnology. If we are able to specifically biofunctionalize small arrays of a solid surface, which could be an electrode or a semiconductor, this approach will enable us to build up devices called “biochips” or “biosensors” that allow the determination of bioactive molecules with high specificity at lowest concentrations. Potential pharmacological active substrates might be screened as well as new receptors may be determined. Applications in genomics as well as proteomics are realistic. The major prerequisite for such a broad spectrum of applications is the fabrication of receptive surfaces. Biomolecules have to be surface‐adsorbed in a highly reproducible, oriented and well organised fashion, a task which in biology is taken by the cellular membranes as external or internal receptive surfaces. The physical principles like hydrogen bonds, electrostatic or hydrophobic interactions that lead to such an organized surface are well known. To synthesize molecular building blocks and to position them onto an otherwise unspecific surface is one of the challenges of nanobiotechnology combining biological knowledge and chemical skills with biophysical techniques that allow to handle or analyze even single molecules.