Oberflächenbeeinflussung von Modellschlagleisten durch Stoßkontakte mit Betonpartikeln

The influencing of the surface of an impeller bar pattern by impact contacting with concrete particles The wear appearing as a result of an impact strain by abrasion particels in an impact- crusher was simulate with a special test machine. With the impact wear test machine were investigated the effects of impacts at different groups of materials to investigate the wear behaviour versus the number of contacts. In view of the abrasive behaviour of the materials the tests demonstrate the necessitiy to consider the penetrating ability of the abrasive particels in the surface of the sample. By means of microphotos was developed a structural model for the abrasion of ductile areas of the material.     

Das Kriechverhalten von Warmarbeitsstählen mit 5% Chrom

Creep Behaviour of Hot-Work Tool Steels Comparison of four steels with varying hardening and annealing treatment. Creep test of up to 200 h duration under constant stress at 550°C. Investigation of carbides by x-ray diffraction of electrochemical residues and electron diffraction of extraction replicas. Marked strengthening at the beginning of creep due to carbide precipitation followed by a decrease in strength due to carbide growth and formation of cells. Up to 1000 h the steel X 40 CrMo V 51 seems to offer the best creep strenght when hardened from 1100°C.     

Oberflächenpräzisionsbearbeitung mit Ionenstrahlen

Low energy ion beam processing becomes more and more established in the development and manufacturing of high precision surfaces as a final complementary step of the conventional surfaces polishing of special optical and mechanical parts. The presented paper gives a comprehensive overview about different ion beam processing techniques and demonstrates the applicability of the ion beam figuring to the final correction of high precision surfaces.     

Untersuchung von Oberflächenschutzschichten von Gasturbinenlegierungen

Investigations on protective coatings on gasturbine alloys. It has been found by investigations of specimens of a combustion chamber pilot plant and also by experiences with gasturbines that aluminide or chromium aluminide coatings are only slightly protective under working conditions of industrial gasturbines. Chromium coatings have a distinctive better protective efficacy and are surpassed in this quality by silicide coatings. It was possible to give information on the development of silicide phases on Nimonic 105. Under the conditions of corrosive attack a surface layer of Nickelolivine is formed and the silicide phases are changed in direction of ternary phases. Even when chromium sulfides are formed in the silicide layer the specimens are stable under the test conditions. By investigations on an airfoil made from B 1900 with a protective coating of Aluminium and Silicon the presence is shown of a ternary Laves phase with Silicon.     

Charakterisierung des tribologischen Verhaltens von keramischen Gleitpaarungen mit moderner Oberflächenanalytik

Characterization of the Tribological Behaviour of Ceramic Sliding Couples with Modern Surface Analysis Methods Dry friction and wear tests were performed in ambient atmosphere with various self-mated couples of SiC, Al₂O₃, Si₃N₄ and ZrO₂. The temperature was varied between 22 °C and 1000 °C and the sliding velocity between 0.03 m/s and 5 m/s. Normal force, temperature and sliding velocity are kept constant during the tests. The materials and wear mechanisms were characterized by various surface analytic methods – optical microscopy, scanning electron microscopy, transmission electron microscopy, electron microprobe analysis, IR-spectroscopy, X-ray diffraction, auger electron spectroscopy and X-ray photoelectron spectroscopy. High wear/low wear transitions could be explained. On the basis of these results new ceramic materials with lower friction and/or wear were selected or successful developed.     

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.     

Modellierung der Stängelkristallitbildung beim Hartlöten von Kohlenstoffstählen mit Kupfer

Simulation of columnar crystallite formation in brazed seams of copper‐brazed carbon steels When brazing steels of different carbon content with copper filler metal, columnar crystallites form on the carbon‐rich iron surface if the width of the brazing gap is smaller than 100 μm. Braze seams with such microstructures were described as early as the 1950ies and it was found out, that the strength of such a joint is significant enhanced, if this crystallites penetrate the entire seam. Extensive experimental investigations in recent years confirm, that the final average length of the crystallite increases superproportionally with decreasing brazing gap width and is almost inversely proportional to the difference in carbon content of the joined steels. Although many attempts to explain this phenomenon are known from literature, the mechanism of columnar structure formation has not been clarified properly until now. The aim of the present work was to develop an appropriate physical model, that describes the growth of crystallites as a function of carbon content in the base materials, the initial brazing gap width and the applied process parameters (temperature, time). The model is an appropriate tool for a general choice and development of filler metal‐base material combinations forming columnar crystallites in the braze seam.     

Der Einfluß von Temperatur und Zeit beim Schweißen von Baustählen mit Strahlen hoher Intensität

Temperature and Time Dependent Fusion Welding with Beams of High Intensity By a special set-up very high local and time-dependent temperature gradients were measured in the weld zone of beam affected areas. Under certain weld conditions a leading preheat wave does not exist. As to the resulting microstructure in the beam, the characteristic steep temperature curves do not allow any prediction. Zones of enlarged hardness were reduced by different heat-treatments.     

Konstruieren mit neuen hochfesten Stählen mit niedrigem Ausdehnungskoeffizienten

Designing with new high-strength low-expansion steels The potential of high-strength low-expansion steels has been illustrated by a series of specific design examples through comparing performance against that of alternative materials. The new products have advantages where large temperature excursions are encountered in piping and pressure vessel applications. The benefits to be gained through using the alloys in the design of labyrinth seals are also demonstrated. Finally the position with respect to diesel engine combustion chamber components is examined, and the alloys are shown to be better than alternatives. Apart from the different design requirements in the above applications, other possible applications are suggested, based on this work which has shown one of their main design merits to be low expansivity coupled with low moduls resulting in very low thermal stresses.     

Verhalten von Stählen unter Hohlladungsbeschuß

Behaviour of Steels under Shaped Charges Bombardement. There is at present not too much known about the behaviour of steel under the very high pressures of some 100 kbars as they will be produced by the hydrodynamic jet force stream of a shaped charge. In a short revue the hithero existing knowledge of the formation of a jet force stream is given as the phenomens in the penetration process of a material. It is recognized by bombardement tests on iron and steels of different compositions and of different heat treatments that there are some changes of the structure near the boundaries of the penetration channels. There is given some information by light- and electronmicroscopical investigations about the occurence during the hydrodynamic penetration process of the jet force stream and about the behaviour of the different structures under local concentrated pressures of shock waves. Microprobe-analyses and scanning electron microscope micrographs supply the understanding.     

Erfahrungen mit Warmwasserbereitern aus nichtrostenden Stählen

Experience with Water Heaters of Stainless Steel . Different stainless steels and their importance in the construction of domestic water heaters. Types of corrosion and their importance in water heating practice. Important aspects for manufacture. Experience gained with stainless steel water heaters.     

Verzug von Stählen infolge Wärmebehandlung

Distortion of Steels Due to Heat Treatment Distortion comprises size and shape distortion. Size distortion is brought about by thermal stresses and structural changes, mainly by hardening and tempering. Thermal stresses cause size-dependant, structural changes size-in dependent distortion. Size-distortion is a system property. Tempering at room temperature over a long period of time influences the size stability. Material anisotropy leads to directional distortion. Shape distortion or warpage originates in residual stresses and differences within the material. Further a nonsymmetrical temperature distribution or geometry of the part have to be considered.     

Zur Zähigkeit von Vergütungsstählen

On Toughness of Quenched and Tempered Steels Toughness as consumed fracture energy is dependent on fracture mechanism. Grain size and loading conditions influence the transition from ductile dimple fracture to brittle cleavage fracture. In quenched and tempered steels packet size and particle distribution are of importance as well as brittle intergranular fracture modes by grain boundary segregation of impurities in ferrite (temper embrittlement) or precipitates in austenite. Anisotropy of toughness arises from banded structures.     

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.     

Oberflächenbehandlung nach spanender Formgebung durch ein einfaches Zusatzverfahren

A supplementary mechanical treatment to strengthen surfaces after machining In this work, a surface treatment is presented in which a hard metal tool insert with rounded edges is pressed on a machined surface at low speed and optimized pressure. This treatment can be executed on the same lathe used previously for machining. The effects on surface topography and surface layer properties (microhardness and X-ray peak halfwidth profiles, as well as residual stresses) have been quantitatively determined. In copper specimens, the surface treatment leads to compressive residual stresses and to strong surface layer deformation and, thus to an increase of near-surface hardness. This effect decreases the amplitude of plastic deformation in the surface layer during fatigue and results in a 25% increase of the fatigue strength at 10⁷ cycles. In Al-2024 T6, the surface treatment causes high compressive residual stresses, an increase in superficial hardness and smoothing of the surface topography. This results in an improvement of the fatigue strength at 10⁷ cycles of 48%.