Günter Bräuer

Reduction of wear at hot forging dies by using coating systems containing boron

The near surface area of forging dies is exposed to high mechanical loads. Additionally thermal and chemical stresses appear during the hot forging process. Depending on the number of forged parts, several kinds of stresses occur in the near surface area, which lead to the initial failures of forging dies. Wear is the main reason for production downtimes with a ratio of 70%. Furthermore, thermal and mechanical cracks are typical causes for failures causes as well as plastic deformation. In order to reduce wear, the abrasion resistance of the forging die surface has to be increased. Hence, different methods like plasma nitriding and optional additional thin hard coatings (TiN, TiCN, TiC, TiBN and TiB2) were successfully examined. Recently developed Ti–B–N coatings in specific multilayer designs are thermally stable, wear-resistant and anti-adhesive regarding the sticking of work piece material. This paper presents the wear reduction possibilities of boron-containing multilayer coating systems applied to forging dies by using the plasma enhanced chemical vapor deposition treatment. A basic mechanical and analytical characterization of different coating systems is realized in the first stage of the project. Best qualified multilayer coating variants were applied to forging dies for experimental investigations. As a result of the tests, wear can be reduced significantly by using thermally stable boron multilayer coatings. To receive realistic wear values under production conditions, an automated forging process was used for testing. After 3,000 forged parts, the coatings were examined by tactile measurement, SEM and EDX analyses to characterize the occurring wear.

New sputtering concept for optical precision coatings

The deposition of optical precision coatings on glass by magnetron sputtering is still a challenging problem regarding particle density and long term stability of coating plants due to target material erosion. A novel approach to increase process stability and reduce drifts is the usage of cylindrical cathodes. These cathodes allow a particle free deposition process as they have virtually no redeposition zones that can lead to destruction of coatings by arcing caused by surface charges. In the present paper optical single layers as well as multilayer coatings were sputtered by means of reactive magnetron sputtering using a double cylindrical cathode setup. The particle density is determined and compared to particles produced with planar magnetrons. A new sputter coater concept will be presented wherein the magnetrons are attached to a rotating disc coater in a sputter-up configuration. The process was stabilized by means of oxygen partial pressure control. Preliminary optical properties as well as deposition rates of different oxide films will be presented.

Optical properties of silicon titanium oxide mixtures prepared by metallic mode reactive sputtering

In this paper different SiO(2)-TiO(2) mixtures are prepared by metallic mode reactive sputtering. The samples were sputtered from cylindrical targets in a sputter-up configuration using an additional plasma source for oxidization. The different ratios of SiO(2) and TiO(2) in the mixtures are prepared by a target sputtering power variation. Optical film properties of the mixtures such as refractive index, which is determined by ellipsometric measurements, and optical bandgap, which is measured by photometric (transmission) measurements, are investigated. The thin-film structure is investigated by x-ray diffraction analysis and the stress of the films is presented. It is shown that the metallic mode reactive sputtering in the present configuration is applicable to continuously tune optical and mechanical properties. Finally the sputtered mixed materials are compared with other optical standard materials such as Nb(2)O(5), Ta(2)O(5), HfO(2), and Al(2)O(3).

Large area deposition

The preferred process for deposition of high precision thin films on large areas (glass panes of up to 3.2 m in width, transparent plastic foils of up to 2 m in width or large metal sheets) is magnetron sputtering.

Surface and coating technologies

The surface of an object is what defines our perception of it. Surfaces are not generally perfect, but their utility value and aesthetic appeal can be enhanced by suitable treatment. Coating techniques can be used to improve the way materials and products look and perform. Important examples include wear-resistant coatings on tools or machine parts and thin films on panes of glass that optimise transmission or reflection in selected parts of the electromagnetic spectrum. Many innovative products would not even exist without the special properties provided by thin films. Prominent examples are computer hard discs, optical data storage media like CDs, DVDs and Blu-ray, flat displays and thin-film solar cells.

Investigations of Electron Beam Hardening on TiAlN Coated Heat-Treatable Steel

In this investigation, an electron beam hardening (EBH) procedure was applied to heat-treatable steel 51CrV4 coated with Ti(1-x)AlxN hard coatings, where x ranged from 0.3 to 0.6. The coatings with variable composition and mechanical properties were deposited by reactive magnetron sputtering. For electron beam surface hardening following hard coating deposition, the energy distribution within the energy transfer field caused a nearly constant hardening temperature on the treated material surface. Morphology, composition, and mechanical properties of the coatings remained mostly unchanged, whereas the coating-substrate interface and the steel surface region were highly modified. Diffusion of the near-interface coating elements into the substrate occurred, and the corresponding region of the substrate showed clear changes in morphology and composition. These changes can be correlated with substantial improvements of the coating adhesion properties. Based on temperature measurements and calculations of electron penetration depths, a plausible description of the observed effects was derived. The EBH caused a significant improvement of delamination resistance, especially for coatings with insufficient adhesion properties.

Matching of maximum gauge factor and TCR zero crossing of Me-DLC

Metal containing diamond-like carbon (Me-DLC) is a promising material for temperature compensated thin film strain gauges with high strain sensitivity. The discussed material offers gauge factors above 10 at zero crossing of the temperature coefficient of resistance. With Ni-DLC the best results so far were obtained. Based on the results from static deposition an industrially suited process under dynamic conditions was investigated. In both cases gauge factors of approximately 10 could be realized. But there is still room for further improvement. Additionally, Fe-DLC seems to be an interesting alternative. First investigations show gauge factors up to approximately 8 with reasonable temperature compensation.

Fabrication of Magnetic Layers for Electromagnetic Microactuators

For designing and fabricating magnetic microactuators, both soft and hard magnetic materials may be required. For soft magnetic materials, a high saturation flux density Bs and a great relative permeability µr is desirable; for forming efficient permanent magnets, hard magnetic materials require a high maximal energy product |BH|max. In the area of soft magnetic materials, investigations on NiFe81/19, NiFe45/55, and CoFe were carried out, while an example for a hard magnetic material providing a high energy product is SmCo. Since patterned thin-film magnets feature inferior magnetic properties compared to bulk magnets, a method of determining their magnetic properties was developed.

Metallurgical investigation of electron beam welded duplex stainless steel X2CrNiMoN22-5-3 with plasma nitrided weld edge surfaces

Abstract Duplex stainless steel is common in thick-walled components such as longitudinal welded pipes in the oil and gas industries and as parts of various machines in the chemical and food industries. Electron beam welding is a very suitable method for welding such components. Due to the high power density of the electron beam combined with the decreased evaporation temperature in a vacuum atmosphere, steel with a sheet thickness of up to 150 mm can be welded in one pass. In the case of the electron beam welding of duplex stainless steels, vacuum atmosphere in the working chamber causes a nitrogen effusion from the weld pool. The microstructure of the resulting weld is characterized by an unacceptable high ferrite content, which is the main reason for both low impact toughness and low pitting corrosion resistance. This work focuses on the influence of nitrided weld edge surfaces on metallurgical properties of the resulting welded joint. The aim here is to investigate the effect of increased nitrogen content at the weld edges on nitrogen loss during EB-welding. The welds produced within the experimental work were characterized by means of microstructural analysis and the use of optical and energy dispersive X-ray spectroscopy. It was shown that nitrided weld edge surfaces can compensate nitrogen loss from the weld pool and decrease the ferrite content in the resulting weld.