Elektronenstrahlschweißen an Atmosphäre – von der Entwicklung bis zum industriellen Einsatz

Non vacuum electron beam welding – from development to industrial application Attributable to the increasing degree of standardisation in many fields of industrial manufacturing, the saving of resources and thus the demand for light weight constructions and also the rapid development on the material sector have made joining tasks increasingly complex. This involves the joining method which must meet the metallurgical demands of the base materials to be welded and also the method’s profitability. In this connection, electron beam welding in atmosphere – NV‐EBW ‐ as a joining method is getting more and more important and is, from the side of the industry, becoming increasingly popular. NV‐EBW combines the many, well‐known advantages of electron beam welding in vacuum with the possibility to work under normal ambient pressure. With an equipment efficiency of more than 50 % and very high, achievable welding speeds of up to 60 m/min for aluminium materials, the electron beam in atmosphere is an efficient and profitable tool for welding. Under the direction of Professor U. Dilthey, the ISF has for many years and in close contact with industrial partners carried out research work in the field of the NV‐EBW technology. At that, elementary contribution to the development of rotationally‐symmetrical orifice assemblies and also to the testing and optimization of the method with regard to respective welding tasks has been carried out.     

Einfluß der Behandlungstemperatur beim plasmaunterstützten Gasphasenborieren mittels BCl3

The influence of the glow discharge using BCl₃-H₂-Ar-atmosphere on the characteristics of the obtained boride layers has been investigated by optical emission spectroscopy for different treatment temperatures. Several species have been identified in the discharge. A special effect in respect to corrosive reactions can be ascertained for the density ratio of the species B*/Cl⁺* that is influenced among other factors by the treatment temperature. Considering the discharge conditions it is possible to suppress corrosive reactions on the substrate surface if the process temperature is stepped.     

Untersuchungen zum Temperaturwechselverhalten von Gußeisen – Teil I: Einflußfaktoren auf das Temperaturwechselverhalten,experimentelle Untersuchungen und deren Ergebnisse

Test examining the temperature shift behaviour of cast iron – Part I: Influence on temperature shift behaviour experimental studies, and their results The first part of this article describes and discusses the most important influence on the temperature shift behaviour of cast iron materials. For some unalloyed and low – alloyed cast iron types the resistance to thermal shocks is measured using a test unit observing the temperature shift behaviour. Metallographic studies on tested materials round up the statements judging materials behaviour under thermal testing.     

Betriebsfestigkeit in der Fahrzeugentwicklung – von der Theorie zum Produkt

Durability Evaluation in the automotive engineering – from theory to product The procedures for durability evaluation in the automotive engineering are represented, especially the methods, load assumption, fatigue testing and the regulations for the release and quality control. By practical examples of the vehicle development from chassis, aggregate and body the procedure is described, in particular the used experimental and virtual simulation methods     

Untersuchungen zum Verschleißverhalten von Metall/Metall – Gleitpaarungen aus CoCrMo‐Legierungen

Investigation of the Wear Behaviour of Metal/Metal Bearings of Co Cr Mo – Alloys CoCrMo‐alloys are successfully used for long‐term implants, because of their corrosion and wear resistance as well as their mechanical properties. In order to improve CoCrMo‐alloys for metal‐on‐metal bearings the influence of carbon content on wear behaviour is investigated. Casted or forged CoCrMo‐alloys with a carbon content from 0.008 to 0.48 wt % were studied in ring on disc oscillating tests. Friction torque, weight loss and surface roughness, as well as light and scanning electron microscopic investigations of the sample surface were used to characterize the wear behaviour. – All alloys show similar friction torque and weight loss. But the surface roughness and the wear mechanisms are depended on the carbon content.     

Experimentelle Charakterisierung und zweidimensionale Simulation der mikrostrukturbestimmten Ermüdungsrissausbreitung in einer β‐Titanlegierung

In this project the initiation and propagation of short fatigue cracks in the metastable β‐titanium alloy TIMETAL®LCB is investigated. By means of an interferometric strain/displacement gauge system (ISDG) to measure the crack opening displacement (COD) and the electron back scattered diffraction technique (EBSD) to determine the orientation of individual grains the microstructural influence on short crack initiation and growth can be characterized. Finite element calculations show a high influence of the elastic anisotropy on the initiation sites of cracks. Crack propagation takes place transgranulary along slip planes as well as intergranulary along grain boundaries. The crack growth rate depends strongly on the active mechanism at the crack tip which in turn is influenced by crack length, the applied stress and the orientation of the grains involved. The value of the steady state crack closure stress changes from a positive value at low applied stresses (roughness induced) to a negative one at higher applied stresses (due to plastic deformations at the crack tip). The crack growth simulation is realised by a two‐dimensional boundary element technique, which contains the ideas of Navarro und de los Rios. The model includes the sequence of the applied stress amplitude as well as the experimental measured roughness induced crack closure.     

ESCA – Untersuchungen zum Aufbau von Oxid-Schichten auf austenitischen Stählen nach Salpetersäurebeanspruchung.

ESCA – Investigations of the Passive Films Formed on Austenitic Stainless Steels in Nitric Acid By means of ESCA the composition and the thickness of passive films formed on austenitic stainless steels were investigated after the attack of nitric acid at various temperatures and acid concentrations. The outermost layers of the oxide film consist of SiO₂, then a layer rich of Cr-oxid follows, containing also some Mo in the four- and six-valent state. Ni does not contribute to the oxide film. Cr is also enriched in the metal just below the oxide film.     

Einfluß der Abkühlgeschwindigkeit auf die δ-Ferrit-Ausscheidung im austenitischen Schweißgut

Influence of the Cooling Rate on the Separation of δ-Ferrite in Austenite Weld Metal There exists a lot of literature concerning the significance of δ-ferrite in welding joints of austenitic stainless steels. An information about the influence of the cooling rate on the primary cristallisation is even more limited. The present results show, that the δ-ferrite-quantity measured at room temperature is hardly influenced by the cooling rate. Furthermore the cooling rate seems to influence the primary cristallisation. The well-known result was verified, that the orientation of the polished section plane yield different δ-ferrite-quantities. Moreover it is shown, that the toughness and therefore the critical crack length increases with decreasing δ-ferrite-quantity.     

Flussmittelfreies Hartlöten unter reaktiver Prozessgasatmosphäre – ein alternatives Verfahren zum Fügen von Aluminiumwerkstoffen

Flux‐free brazing under reactive process gas atmosphere – an alternative process for joining of aluminium materials Due to the high affinity of aluminium towards oxygen, joining of aluminium materials has ever been a challenge. In particular the efficiency of the process and the abandonment of fluxes during controlled atmosphere brazing have been within the focus of current research projects. The specific addition of reactive gases to the inert process gas atmosphere offers a suitable possibility of aluminium brazing without the use of fluxes. Under the application of hydrogen chloride the activation of the brazing and the workpiece surfaces is to be initiated, thus leading to dissolving the oxide layers. Moreover, the strongly reducing gas silane is used, which specifically removes oxygen and water residuals from the controlled atmosphere. Through a suitable controlled atmosphere brazing process the combination of both, reductive and activating additions, is to be used and tested upon their influence on the gas mixtures and materials used [1–5].     

Einfluß der Wärmeermüdung im Tieftemperaturbereich (77 K ⇔︁ 373 K) auf mechanische Eigenschaften der (α + β)-Ti-Legierung

Effect of the low-temperature thermal cycling (77 K ⇔︁ 373 K) on certain mechanical properties of a two-phase (α + β)-titanium alloy The paper reports an investigation on the effect of low-temperature thermal cycling (LTTC) within (77 K ⇔︁ 373 K) range on select mechanical properties and crystal lattice parameters of the constituent phase, α and β, of a double-phase titanium alloy as determined at temperatures of 295 K and 77 K. Fatigue tests were conducted under plane bending conditions at stresses exceeding the material endurance limit. It was found that the LTTC effects were closely related to the number of thermal cycles applied: after 100 cycles the fatigue strength at the two temperatures rose by 30% as compared with the no-LTTC condition: after 500 LTTC cycles a pronounced drop in the fatigue strength was observed ′ 87% at temperature of 295 K and 30% at 77 K. Microscopy and X-Ray studies showed that twinning had a significant effect on both the LTTC and mechanical fatigue processes. Residual stresses arising during the LTTC treatment were found to be a stimulating factor in the development of deformational processes occurring in the loaded material.