Kristallseigerungen und eutektische Carbidausscheidungen in Eisen-Kohlenstoff-Vanadin-Legierungen

Untersuchung des Einflusses der Legierungszusammensetzung auf Kristallseigerung und Ausscheidung eutektischer Carbide von Eisen-Kohlenstoff-Vanadin-Legierungen mit 0,35 bis 2,10% C sowie 0,60 bis 4,40% V. Aussagen über den Einfluß des Kohlenstoffgehaltes auf die Seigerung des Vanadins und die Carbidbildung bei gleichbleibendem Gesamtvanadingehalt. Vergleichende Betrachtung über die Wirkung der Legierungselemente Chrom, Molybdän, Wolfram und Vanadin auf Kristallseigerung und eutektische Carbidausscheidung.     

Binary search trees with binary comparison cost

We introduce a new variant of the cost measure usually associated with binary search trees. This cost measure BCOST, results from the observation that during a search, a decision to branch left need require only one binary comparison, whereas branching right or not branching at all requires two binary comparisons. This is in contrast with the standard cost measure TCOST, which assumes an equal number of comparisons is required for each of the three possible actions. With BCOST in mind we re-examine its effect with respect to minimal and maximal BCOST trees, minimal and maximal BCOST-height trees, and introduce a class of BCOST-height balanced trees, which have a logarithmically maintainable stratified subclass. Finally, a number of other issues are briefly touched upon.This work was partially supported by NATO Grant GR 155.81, Natural Sciences and Engineering Research Council of Canada Grant No. A-5692, and National Science Foundation Grant No. MCS-8116522.     

Concept and procedure of the IRC test for assessing hydrogen assisted weld cracking

The self restraining Instrumented Restraint Cracking (IRC)-test enables the determination of weld joint reaction forces and -moments responsible for hydrogen assisted cracking. With help of continuous measurements during cooling of the weld, the effects of crack inducing parameters can be detected in detail. The IRC-test can be applied to procedure development and procedure qualification welding, making use of current fabrication practice at restraint intensities of the to-be-fabricated structure. It is easy to carry out and the results are quickly at hand.     

Kristallseigerungen und eutektische Carbidausscheidungen in Eisen-Kohlenstoff-Wolfram-Legierungen

Untersuchungen zur Kristallseigerung und Primärcarbidausscheidung von Eisen-Kohlenstoff-Wolfram-Legierungen mit 0,5 bis 2,2% C und 1,0 bis 12,4% W sowie < 0,35% Si, < 0,55% Mn, < 0,03% P und < 0,04% S. Aussagen über die Kristallseigerung des Wolframs in Abhängigkeit vom Kohlenstoffgesamtgehalt bis zum Erreichen der Carbidsättigung der Mischkristalle. Zusammenhang zwischen dem Anteil an Primärcarbiden und wachsenden Kohlenstoffgesamtgehalten bei konstantem Wolframgehalt. Ermittlung unterschiedlich hoher Anteile der beiden Carbide M₆C und M₃C. Einfluß einer Homogenisierung auf die Beseitigung der Kristallseigerung und die Ausscheidung wolframreicher Carbide.     

Current routes in polycrystalline CuInSe2 and Cu(In,Ga)Se2 films

Local electrical transport measurements with scanning probe microscopy on polycrystalline (PX) p-CuInSe₂ and p-Cu(In,Ga)Se₂ films show that the photovoltaic and dark currents for bias voltages smaller than 1 V flow mainly through grain boundaries (GBs), indicating inversion at the GBs. Photocurrent for higher bias flows mainly via the grains. Based on these results and our finding of 100 meV GB band bending we deduce the potential landscape around the GBs. We suggest that high grain material quality, leading to large carrier mobilities, and electron–hole separation at the GBs, by chemical and electrical potential gradients, result in the high performance of these PX solar cells.     

Fertilizers, agronomy and N2O

N₂O is emitted from agricultural soils due to microbial transformation of N from fertilizers, manures and soil N reserves. N₂O also derives from N lost from agriculture to other ecosystems: as NH₃ or through NO ₃ ^- leaching. Increased efficiency in crop N uptake and reduction of N losses should in principle diminish the amount of N₂O from agricultural sources. Precision in crop nutrient management is developing rapidly and should increase this efficiency. It should be possible to design guidelines on good agricultural practices for low N₂O emissions in special situations, e.g. irrigated agriculture, and for special operations, e.g. deep placement of fertilizers and manures. However, current information is insufficient for such guidelines. Slow-release fertilizers and fertilizers with inhibitors of soil enzymatic processes show promise as products which give reduced N₂O emissions, but they are expensive and have had little market penetration. Benefits and possible problems with their use needs further clarification.     

Characterization of silicon phases in spray-formed and extruded hypereutectic Al–Si alloys by image analysis

The silicon phases in the spray-formed and extruded hypereutectic Al–Si alloys (AlSi18, AlSi25 and AlSi35) have been quantitatively evaluated by means of image analysis technique. The influence of silicon content in the alloys, thermal conditions during spray forming of the alloys and hot extrusion of the spray-formed alloys on the size, shape, dispersion and orientation of the silicon phases have been studied and discussed. In general, the silicon phases are greatly refined and uniformly distributed in the spray-formed Al–Si alloys. This improvement in the silicon phases is further facilitated by low thermal input as well as fast cooling conditions during spray forming. The silicon particles in the as-extruded Al–Si alloys appear more homogeneous and regular than those in the as-deposited Al–Si alloys but exhibit a certain amount of anisotropy and a tendency to preferred orientation. The silicon particles, depending on the particle size and shape, may fracture or coarsen during extrusion.     

Heterogeneous phase equilibria as a basis for crevice corrosion modelling

The presented crevice corrosion model is intended to provide basic understanding of formation and dissolution of passivating layers during time dependent metal dissolution in an already deoxygenated crevice. It operates along a constant cathodic polarization curve in subsequent time steps with time dependent anodic polarization curves and corrosion currents. The anodic polarization curves are determined by dissoluted ionic chromium and respective Nernst potentials as well as by the mass of precipitated passivating chromiumhydroxide layers. All chemical reactions including diffusion of chloride into the model crevice configuration are assumed to be at equilibrium during the respective time steps. The amounts of passivating chromiumhydroxide masses are determined by lever-rule application at increasing chromium and chloride contents in aquaeous solution of the quaternary water-chromium-hydrogen-chloride phase diagram at various Nernst potentials. For this purpose, the established water–chromium Pourbaix diagram had to be redrawn in terms of ternary water-chromium-hydrogen phase diagrams for constant potentials. It was tentatively extended to the quaternary chloride including diagram based on literature results. This included solubility of chromiumchloride in hydrochloric acid and most probable effects of chloride ions on chromiumhydroxide solubility at saturation with chromium metal. The results of the interactive corrosion process are based on a crevice geometry drawn from previous publications and given initial solution concentrations as well as assumed polarization curves for time steps of one second. It is shown, how the process starts with concentration changes of chromium, chloride and hydrogen in the crevice, the subsequent formation of the passive layer and the corresponding decrease in the corrosion current and increase in the mixed potentials. In the presence of the chromiumhydroxide phase, however, chromium and hydrogen remain at low levels in the equilibrium aqaeous solution while chloride is increasing. The saturated solution reaches the four phase equilibrium concentration including saturation by chromium, chromiumhydroxide and chromiumchloride at corresponding Nernst potentials. The further increase in total chromium and chloride concentrations of the crevice then leads to initiation and propagation of crevice corrosion by formation of non-passivating chromiumchloride at the expence and finally, the total dissolution of passivating chromiumhydroxide, at decreasing mixed potentials and increasing currents. Due to the low solubility of chromiumchloride in hydrochloric acid, the latter is finally formed with the result of the well-known increase in crevice acidity. Thus, it is demonstrated that the acidification itself is not a requirement for crevice corrosion but rather a consequence of it.