Verhalten von Hochtemperatur-Lötverbindungen bei schwingender Belastung und erhöhten Temperaturen

Fatigue behaviour of High Temperature Brazed Joints tested at elevated temperatures Fatigue testing, on a systematic and statistical basis, was carried our on high temperature brazed joints produced in the base metal NiCr20TiAl joined with BNi-5 and BAu-4 filler metals. The single-stage tests were conducted with various temperatures of 500 and 700 °C. Microscopic examination of the fracture surfaces (SEM) yielded information about crack initiation and propagation and the fracture behaviour of the joints.     

Das Kriechverhalten von stickstofflegierten,austenitischen Stählen mit erhöhter Festigkeit bei Raumtemperatur

The Creep Behaviour at Room Temperature of Higher Strength Austenitic Steels containing Nitrogen. The mechanical properties of special austenitic steels with increased Cr and Ni contents and N₂ content up to 0,35 % have been investigated. In the as-received condition i.e. annealed and water quenched, the 0,2 % offset yield strength of these steels ranges from 400 to 500 N/mm². However, regardless of these increased yield strengths, the stress-strain characteristics are the same as for conventional austenitic steels. Since first plastic deformations correspond to an applied stress equal to 50 % of the 0,2 % yield strength, in practical applications the creep behaviour of these steels may be significant. Therefore, the creep behaviour at room temperature of the base metals and weldments has been investigated to determine the influence of thermal and mechanical treatments after annealing. The elastic limit of airquenched steels is significantly higher than of water-quenched, even though the 0,2 % yield strengths are essentially the same. This different stress-strain dependence influences the creep behaviour of the steel. The cold working of these steels by plastic straining in both tension and compression results in a useful strain hardening effect only when the direction of applied stress is the same as the stress during cold working. When the direction of stressing was reversed, a considerable Bauschinger-effect was observed.     

Heißrißgefahr beim Elektronenstrahl-Schweißen metastabiler austenitischer Werkstoffe

The Risk of Hot Cracking during Electron Beam Welding of Metastable Austenitic Steels Electron beam welding of austenitic steels is an economic process for joining heavy section structures. Beside the technological advantages as there are low weld distortion, small shrinkage ratio and deep weld effect resulting from the concentrated heat input several problems arise when a metastable austenitic steel is electron beam welded. The high cooling rate may lead to a primary austenitic solidification of the weld pool increasing the risk of hot cracking. Therefore investigations in electron beam welding with the tulip-shape seam technology were carried out. The results show that the primary austenitic solidification and in consequence the risk of hot cracking can effectively be interfered by the addition of ferrite forming elements. With regard to industrial application an additional alloying wire filler offers itself to be a suitable procedure.     

Ermittlung des Versagensverhaltens thermisch gespritzter MCrAlY/IN617-Verbundwerkstoffe im Zugversuch bei Temperaturen bis 800 °C im Rasterelektronenmikroskop

Fracture mechanisms of Thermally Sprayed MCrAlY/lN617 Composite Materials during Tensile Tests up to 800 °C Tensile strength of thermally sprayed MCrAlY/IN617 composite materials has been prooved at temperatures up to 800 °C in a SEM. For these investigations two different qualities of composite materials have been developed. One sort of composite material had been produced with a good quality, the other one was produced with defects in the coating layer. The tensile strength of the good homogeneous material shows no dependence with increasing temperature, whereas the inhomogeneous composite materials develop better strength values with increasing temperature. The inhomogeneous coating always breaks in the near of the defect.     

Thermal analysis by a constant heat flow

A new method of and apparatus for thermal analysis is described, whereby the heat flow fed by the oven to the sample is kept constant as a function of time. The measurement gives the change of enthalpy in heating or cooling the sample. From this enthalpy–temperature relationship quantitative thermodynamic results are easily obtained. Transitions of first and second order in polymers can be measured in one run.     

Beitrag zum Lebensdauerverhalten und zur zerstörungsfreien Bewertung geschweißter und fehlerbehafteter ultrafester Stähle

Relationship between fatigue behaviour and non-destructive assessment of weld defects of TIG-welded ultra-high strength steels With respect to the influence of welding defects on the fatigue properties of welded high strength special steels and on the dynamic load carrying capacity of joints in welded constructions, a minimum of information is available. For this reason, the preparation of an assessment standard for classifying weld defects was considered practical, whereby the character of the defects was to be determined using non-destructive testing methods. The investigations were concerned with a special method of producing specimens containing defined and reproducable defects, with the characterization of the defects using X-ray and ultrasonic techniques, and with the determination of the influence of the weld defects on the fatigue strength of TIG-welded joints. As a result of the investigations, a relationship between allowable and critical defect size with respect to an assessment standard has been sought. By introducing weighting factors for various types and sizes of defects occurring in welds the efficiency of non-destructive testing methods for the assessment of weld defects is considerably increased.     

Bedeutung und Vorteile des Einsatzes von Fetten in der Fischernährung

Fische sind, je nach Art, auf die Zufuhr von Fettsäuren der n-3- und/ oder n-6-Reihe angewiesen. Fette sind gut verdauliche Energiequellen für Fische. Durch ein zweckmäßiges Protein/Energie-Verhältnis (Hochenergiefutter) sind eine günstige Futterverwenung, ein schnelles Wachstum sowie eine rationelle Protein- und Energienutzung zu erreichen. Mit Hilfe von (fettreichem) Hochenergiefutterlassen sich die Kotabgabe, die N-Ex-kretion und die P-Ausscheidung der Fische stark reduzieren. Damit wird ein wesentlicher Beitrag zur Verringerung der Gewässerbelastung mit Nährstoffen geleistet. Durch die Wahl von Fischölen als Futterkomponenten kann die Fettsäurezusammensetzung der Fische positiv beeinflußt werden. Fische mit hohem Gehalt an n-3-Fettsäuren stellen wertvolle Nahrungsmittel dar, die zur Prophylaxe und Therapic von Herz-Kreislauf-Erkrankungen geeignet sind. Importance and benefit of using lipids in fish nutrition. According to species fish require fatty acids of the n-3 and/or n-6 type. Lipids are well digestible energy sources for fish. By appropriate protein:energy ratio (high energy feed) favourable diet utilization, fast growth and efficient protein and energy utilization may be achieved. Feeding fat enriched high energy diets leads to considerable reduction of faecal, nitrogen and phosphorus excretion of fish. This contributes to a decrease in the nutrient load of waters. When using fish oils as dietary ingredients the fatty acid composition of fish can be influenced positively. Fish containing high levels of polyunsaturated fatty acids are valuable foodstuffs which are beneficial to prophylaxis and therapy of cardiovascular diseases.