Modifizierte Nickelbasisstandardlote für korrosiv belastete Bauteile

Modified nickel based standard brazing filler metals for units under corrosive loads Nickel‐based alloys are presently used as brazing filler metals for components which undergo mechanical stress in corrosive conditions, f. e. heat exchangers. When soldering chrome containing steel parts with nickel based brazing filler metals additionally containing boron and silicon a reaction of chrome and boron can occur. This evolution of chromium borides, depositing on grain boundaries, causes a lack of chrome in the steel part. A drop of the chrome content in the parts below 13 % leads to a loss of corrosion resistance. It is possible to change the microstructure of brazing joints by modification with chromium and molybdenum. Continuous brittle phases could be successfully avoided with this modification. Furthermore it could be shown that the choice of additives, the heating respectively cooling rate and the brazing temperature have important influence on the microstructure evolution and therefore on the mechanical and corrosive properties of joints.     

Werkstoffoptimierung für schwingbeanspruchte Bauteile

Choice of Optimum Materials for Fatigue Loaded Structures . In many modern lightweight structures, repeated loads must be considered. The fatigue properties under these loads are determined by the material choosen as well as the design quality achieved and the production methods used. For satisfactory service behavior the following materials properties must be established: By means of many examples, these properties are discussed in some detail. It is shown that the high static strengths achieved in some modern materials generally lead to a deterioration of the properties mentioned above; therefore the successfull use of these materials requires detail design of very high quality, special production methods and effective non-destructive inspection procedures.     

Erprobungsmethodik für zyklisch überelastisch beanspruchte Bauteile unter Torsion – Bauschinger‐Kenngrößen für 54SiCr6

Power transmission contains several torsion‐stressed parts. Especially shafts and springs are numerous considered. Helical springs as a special type of springs are mainly stressed by torsion load. During operation the spring's load is basically elastic. In some cases, like overload or machine disaster, the load exceeds the spring's yield stress. For a single event the deformations can be calculated easily by using flow charts. However in other cases the spring will be stressed several times with alternating plastic load. Therefore the calculation will not be as easy as in the single load case. Especially the hardening and softening mechanisms have major influence on material behavior. For high strength steel this material behavior is not fully investigated right now. Present article shows a way how to investigate several important Bauschinger parameters based on plastic torsion load for the high strength steel 54SiCr6. Finally it can be shown that 54SiCr6 is influenced by the Bauschinger effect. On the other hand the needed material characteristic can be investigated by the shown methodology. Based on the identified data, analytical and numerical calculation of alternating plastic torsion load can be done.     

Derzeitiger Stand der Lebensdauervorhersage für Bauteile

The State of the Art in the Fatigue Live Evaluation of Components For fatigue life estimations of components many compromises must be entered in the utilization of available fatigue design data. The parameters of the chosen design data which do not fit the component to be evaluated are in most cases taken into consideration by very global factors. These factors and the inaccuracies of Miner's Rule provide only a rough estimate of the fatigue life of a component. When the component is allready available, these uncertainties can be reduced by performing a fatigue test with service like load-time histories and a relative Miner's Calculation. For the same reason the total knowledge about the service fatigue behaviour of similar components should be taken into account in the life estimation.     

Die Bedeutung der Werkstoffauswahl für die Gebrauchstauglichkeit von Chemieapparaten Auswahlkriterien und Prüfverfahren

Materials selection and service properties of chemical plants – criteria of selection and testing methods . Materials selection and technical design – operating temperature and limit of stress – corrosion and abrasion resistance – corrosion testing methods – testing of corrosion behavior of welded joints.     

Schützende Oberflächen für metallische Werkstoffe

Coatings for Metallic Materials . The most important coating techniques are characterized and critically described. Among the various possibilities to protect the surface of metallic materials against mechanical, chemical or mechanical-chemical attack, the coatings which are looked upon are ranging from metallic coatings over nonmetallic anorganic to the organic ones.     

Gesenkschmieden hochfester Magnesium‐Knetlegierungen für Bauteile der Automobil‐ und Luftfahrtindustrie

Die‐forging of high strength magnesium wrought alloys for the automotive and aerospace industry Forging is an attractive method to produce complex components from magnesium alloys. In this context it is important to choose adequate processing parameters. Magnesium forgings provide superior quality, they are pressure sealed, free of pores and shrinkage and have excellent mechanical properties. The potential of magnesium forgings is very promising, but usage of magnesium forgings is still limited mainly due to the present cost situation.     

Empfehlungen zur Werkstoffauswahl und zu den Schweißdaten für NH3-Lagerbehälter und NH3-Kesselwagen

Recommendations for Selection of Material and welding Electrodes for NH₃-storage Vessel and NH₃-Transport Container In liquid ammonia mostly only weld seams show cracks. Extensive SEM-investigations have shown that these are hydrogen induced cracks. During weld tests with the base materials St E 335 and St E 460 in different charges high yield strengths were determined in the weld material. Very often the yield strength values increase after stress relieving. This is caused by precipitation, which leads to a bracing of the lattice, thus raising the yield point. To ensure one of the base material adapted yield strength in the weld it is only possible in very rare cases with suitable weld additives. In the St E 460 with nitrogen and vanadium the yield strength value in the weld is even by use of the wire S 1 and neutral powder over 600 N/mm². It was found out that hydrogen induced cracks in the weld above 550 N/mm² yield strength occur very likely below 550 N/mm² occur very little. In the base material St E 355 the yield strength was limited for this reason in the weld with 500 N/mm² in the base material St E 460 limited with 550 N/mm². Proof has to be furnished for all welding procedures, sheet charges and weld additives applicable by means of welding probes.     

Einfluß korrosiver Umgebung auf die Lebensdauer zyklisch beanspruchter Bauteile

Influence of a corrosive environment on the fatigue life of cyclic loaded structures Fatigue life of structural components in practice is effected by corrosive environments, too. The failure mainly is caused by the interaction of cyclic straining and corrosive attack. Extensive research and test programmes during the last two decades had been carried out to investigate the parameters influencing corrosion fatigue. Results of the most effective parameters on corrosion fatigue are given in the present paper. The amount of degrading effect on fatigue properties depends on the susceptibility of the material to corrosive environment, the structural shape and the environment itself. The various parameters determing fatigue behaviour are superimposed in a synergistic manner, so their effects cannot simply be added. That may be the reason for very different conclusions on the effect of corrosion on fatigue life from ?disastrous”? to ?neglegible”?. Though there is still a number of unclear points, the good agreement of results of welded specimens (V-shaped specimens) and welded tubular joints indicates a positive outlook for the application of small specimen corrosion fatigue data for the design of structural components.     

Oberflächenschutzschichten für metallische Hochtemperatur-Werkstoffe. Teil 2: Schutzschichten auf Superlegierungen und hochschmelzenden Metallen

Protection of High Temperature Metallic Materials against Oxidation , part 2; Protective Layers on Superalloys and High Temperature Materials. The structures of typical protective coatings of superalloys and Nb-alloys are briefly described and possible reasons for their failure are given. The importance of self-healing properties and of the reliability of such protective layers in any technical application is stressed. An order of magnitude of the duration of protection for different alloys is indicated for several coating types.     

Bedeutung von Prüfmethoden für die Auslegung verschleißbeanspruchter Bauteile

Test Methods and Dimensioning of Tribologically Loaded Parts Owing to the complexity of tribological systems the testing of wear components is of particular significance. Here is an effort to show the advantages and disadvantages of product tests, component tests and model tests. Even with model tests good results for the products are attainable when relevant parameters are systematically varied. Hereto some examples are given.     

Oberflächenschutzschichten für metallische Hochtemperatur-Werkstoffe. Teil 1: Entwicklungstendenzen,Prüfung und Herstellung von Schutzschichten

Protection of High Temperature Metallic Materials against Oxidation . Part 1: Development Trends, Testing and Preparation of Protective Layers. A comparison is given of the chemical compositions of industrial Co- and Ni- high-temperature alloys used in the past years. Due to their relatively low Cr and Al contents the more recent super-alloys require additional oxidation protection. Theoretically, the refractory metals would allow much higher working temperatures than the super-alloys, but alloys based on such metals need a much more perfect oxidation protection. The fabrication testing and methods for such protective layers are briefly reviewed. The second part of this paper will describe some specific protective layers for super-alloys and refractory metals.     

Tribologische Untersuchungen an Gleitpaarungen aus ZrO2, POM und Stahl für den Einsatz als wassergeschmierte mikromechanische Bauteile

Tribological studies on sliding pairs of ZrO₂, POM and steel for applications as water‐lubricated micro‐mechanical components Micro‐tribological tests were carried out on varying mated sliding pairs of TZP‐ZrO₂, polyoxymethylene (POM) and steel 17‐4PH in air and distilled water using a laboratory tribometer (system: flattened ball‐on‐disc) under unidirectional sliding. The effects of relative humidity in air or water lubrication, respectively, the surface pressure and the sliding speed were studied with the self‐mated zirconia. The results show that zirconia can be a favourable material for tribologically high‐loaded micro‐mechanical components at water lubrication, particularly, in comparision with already used polymeric materials. Self‐mated zirconia resulted also during unlubricated sliding in air in lower friction and wear than the steel/steel, POM/steel or POM/ZrO₂ pairs, respectively. Keywords: precision engineering, micromechanical components, sliding wear, friction, water lubrication, zirconia, polyoxymethylene, steel 17‐4 PH.     

Stabilität von Druckeigenspannungen unter zyklischer Beanspruchung für autofrettierte Bauteile aus Aluminium

Autofrettage provides the possibility for increasing the fatigue strength of internal pressurized components. This technique introduces compressive residual stresses, applying a single pressure overload prior to the service load. Whereas a lot of investigations for steel materials have been done so far, this report refers to the potential of the autofrettage process for the aluminum wrought alloy EN AW‐6082‐T5. In order for residual stresses to ensure a reliable increase of the stress amplitude, they must not be relaxed. A significant increase in lifetime at a load amplitude of Δp = 500 bar is shown for T‐shaped bore intersection specimens that are autofrettaged at a pressure of 1500 bar. The introduced residual stresses did not relax after 2.5×10⁶ number of cycles. Only for a load with a maximum equivalent stress above the yield strength the components initial compressive residual stress distribution is changed and even partially transferred to the tensile section. Therefore, using autofrettage is appropriate to increase the fatigue strength of aluminum components.     

Chancen und Hemmnisse für den Metallschaumeinsatz

Chances and inhibitions for the use of metal foam Materials represent more and more the initial key to market success. New developments in material research produce frequently innovative product designs. Metal foam is such an material innovation. It's been characterized by disintegrating solid structures into cellular structures. Metal foam combines excellent properties such as mass‐rigidness‐relation, vibration‐ and acoustic damping, crash‐absorption and thermal insulation effects. Despite its characteristics there is not a single application known in mass production. To investigate its reasons was the purpose of a 1999 initiated opinion poll by the Fraunhofer‐Institute in Chemnitz.