No abstract

No abstract

No abstract

Direct Metal Laser Sintering has real potential for rapid-manufacture applications in the PM arena, reducing lead times and cutting costs. But it has been hampered by the limited range of suitable powders available and their cost. A research group led by Fraunhofer scientists made their own powders and took a closer look...

No abstract

T he aluminium alloy AA 6013 is of increasing signi cance with regard to the aircraft M. SCHNEIDER industry. In addition to its mechanical properties, corrosion resistance, especially against H. POHL local corrosion phenomena ( i.e. pitting corrosion and crevice corrosion), is very important in structural applications. In this work, the authors present the use of electrochemical noise analysis ( EN A) in combination with a corrosion cell design, which was developed for the investigation of crevice corrosion. It is shown that EN A is a very useful technique for the early detection of crevice corrosion processes in the earliest stages of attack.BCJ /1989

The Electrochemical Noise Analysis (ENA) is a novel technique employed to investigate dynamic properties of electrochemical systems. The influence of chromate inhibitors on the corrosion activity of an AA 2024 surface in a chloride containing sodium solution was studied by the measurement of current noise under potential control. The noise analysis clearly shows the efficiency of the chromate inhibitor on the crevice corrosion as well as the sufficiency of the ENA as a useful tool as an inhibitor screening process. The measurement under crevice condition was carried out in-situ in an artificial crevice. Die Elektrochemische Rauschanalyse (ENA) ist eine noch junge Methode zur Untersuchung der dynamischen Eigenschaften eines elektrochemischen Systems. Der Einfluss eines Chromatinhibitors auf die Korrosionsaktivität einer AA 2024 Oberfläche wurde anhand der Messung des Stromrauschens unter Potentialkontrolle untersucht. Die Rauschanalyse zeigt die Wirkung des Chromatinhibitors auf die Spaltkorrosion sehr klar und beweist außerdem, dass die ENA ein hilfreiches Werkzeug bei der Suche nach Inhibitoren sein kann. Die Messungen unter Spaltbedingungen wurden in-situ in einem künstlichen Spalt durchgeführt.

Solid solution hardening and strain hardening are the dominating strengthening mechanisms to achieve a high yield stress and ultimate tensile strength in Cr-Mn-N steels for drill collars. The fatigue limit can be improved more effectively by solid solution hardening than by strain hardening, but the attainable hardness due to soluble elements is restricted by other metallurgical demands. Strain hardening significantly increases the strength and the fatigue limit is improved too, but to a lesser extent. The reason for this behaviour is the introduction of internal stresses of the I, I1 and 111 kind by forging the drill collars. This results in macroscopic stresses which are varying over the cross section and in stresses of a microscopical scale which lead to an early loss of linearity in the elastic line of the stress strain curve and to the well known Bauschinger effect. Cyclic softening and hardening is accompanied by a rearrangement of the dislocation structure as revealed by transmission electron microscopy. The results indicate that a multiaxial and homogeneous cold working to produce a stable dislocation structure and to avoid large directional internal stresses is extremely important to achieve high fatigue strengths. Crack growth and crack closure measurements were performed for determination of the effective cyclic threshold stress intensity range for evaluation of the influence of the grain size on the fatigue limit. 1 NOMENCLATURE A, = elongation after fracture c = fatigue ductility exponent da/dN = fatigue crack growth rate dG = grain size tap, = plastic strain amplitude i = strain rate c; = fatigue ductility coefficient Kmai = maximum stress intensity factor AK = cyclic stress intensity factor range AK,h = threshold stress intensity factor range AK,,,, = effective threshold stress intensity factor range N = number of cycles Nf = number of cycles to failure N, = number of cycles to crack initiation R = load ratio (R = um,n/a,,,) Rp0,* = yield strength R, =tensile strength u = stress u, = stress amplitude pr = relative permeability 2 = reduction of area after fracture Au = stress range