TY - JOUR A1 - Krasnorutskyi, S. A1 - Keil, D. A1 - Schmigalla, S. A1 - Zinke, M. A1 - Heyn, Andreas A1 - Pries, H. T1 - Metallurgical investigations on electron beam welded duplex stainless steels N2 - Thick-walled components made of duplex stainless steels are used in the semi-finished products as well as in machinery, apparatus and plant construction. Electron beam welding (EBW) of these components may be recommended for economic and quality reasons. To guarantee the necessary mechanical and technological properties and the corrosion resistance, the duplex stainless steels are welded with filler material and afterwards undergo a post-weld heat treatment. The present work shows interim results of investigations concerning the development of an electron beam multi-process technology for welding these steels without filler material and post-weld heat treatment. The studies were performed on standard duplex stainless steel of type 1.4462 (X2CrNiMoN22-5-3). When welding duplex stainless steels, the cooling rate and the chemical composition have a crucial influence on the final result. Based on fundamental investigations relating to the influence of the process parameters on the effusion of nitrogen and the cooling rates, the resulting austenite formation, mechanical properties and the corrosion resistance were taken into account to develop appropriate electron beam multi-process techniques. The ferrite content was measured metallographically and by magnetic induction, the impact toughness was measured at –40 °C and the determination of critical pitting temperatures was performed using electrochemical noise measurements. KW - Nichtrostender Stahl KW - Duplex KW - Schweißen KW - Lochkorrosion KW - Mikrostruktur KW - Stickstoff KW - Ferrit KW - Schweißwerkstoff KW - Duplex stainless steels KW - EB-welding KW - Pitting corrosion KW - Microstructure KW - Fracture toughness KW - Nitrogen KW - Ferrite KW - Weld metal KW - Welding without filler PY - 2012 U6 - https://doi.org/10.1007/BF03321393 SN - 0043-2288 SN - 1878-6669 VL - 56 IS - 11/12 SP - 34 EP - 40 PB - Springer CY - Oxford AN - OPUS4-28005 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bender, S. A1 - Goellner, J. A1 - Heyn, Andreas A1 - Schmigalla, S. T1 - A new theory for the negative difference effect in magnesium corrosion N2 - An unusual feature known as the negative difference effect (NDE) can be observed in magnesium when recording corrosion current density–potential curves. More hydrogen is evolved at a more positive potential which does not occur in conventional metals. Several models have been proposed in the literature in order to explain the phenomenon of NDE. They succeed in explaining some effects, and fail to deal with others. A new model, which explains the NDE by two electron consuming processes, is presented in this paper. By potentiostatic investigations of magnesium in a chloride electrolyte, measurements of hydrogen evolution and chemical analysis of the electrolyte the new model was experimentally verified. KW - Magnesium KW - Negativer Differenzeffekt KW - Korrosion KW - Korrosionsmechanismus KW - Current density-potential-curve KW - Magnesium alloys KW - Magnesium corrosion KW - Negative difference effect KW - Polarization measurements PY - 2012 U6 - https://doi.org/10.1002/maco.201106225 SN - 0947-5117 SN - 1521-4176 VL - 63 IS - 8 SP - 707 EP - 712 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-25162 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmigalla, S. A1 - Heyn, Andreas T1 - Determination of critical pitting temperatures for Ni-Cr-Mo alloys using electrochemical noise measurements N2 - The determination of critical pitting temperatures (CPT) in various test solutions like ferric chloride solution according to ASTM G48 or 'Green Death' solution is a common test method for the comparative assessment of the pitting corrosion resistance of highly alloyed steels and Ni–Cr–Mo alloys. In addition to the well-known disadvantages of standard methods, like long test times, subjective examination, and large scatter, for the highest alloyed Ni–Cr–Mo alloys no stable pitting corrosion can initiate even at the highest test temperatures. This paper describes the limitations of standard test methods and shows how these problems can be solved by an alternative test solution and an adjusted test method. By capturing and examining the current noise under potentiostatic conditions during continuous heating in a 4.5 M calcium chloride solution the transition from metastable to stable pitting corrosion as a criterion for CPT can be detected in a reproducible way. KW - Critical pitting temperature KW - Electrochemical noise KW - Ni Cr Mo alloys PY - 2013 U6 - https://doi.org/10.1002/maco.201206910 SN - 0947-5117 SN - 1521-4176 VL - 64 IS - 8 SP - 700 EP - 707 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-29072 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmigalla, S. A1 - Bender, S. A1 - Heyn, Andreas A1 - Schmidt, J. A1 - Hort, N. T1 - Investigation of biodegradation behaviour of an Mg-1Ca alloy influenced by heat treatment and applying plasma-chemical oxidation layers N2 - The degradation behaviour of an Mg-1Ca alloy is investigated in vitro to figure out the possibilities of influencing the degradation behaviour of such an alloy by applying heat treatment as well as the use of a coating system based on plasma-chemical oxidation. It is shown that an optimised solution annealing (T4-heat treatment) can reduce the degradation rate while an additional ageing between 240 and 300 °C (T6-heat treatment) increases it. A coating generated by plasma-chemical oxidation reduces the degradation rate in the immersion test. Its effect is depending on the former heat treatment of the Mg-1Ca alloy as well as on the parameter during plasma-chemical oxidation. KW - Biodegradation KW - Magnesium alloys KW - Plasma-chemical oxidation KW - Magnesium KW - Thermal treatment KW - Corrosion KW - Electrochemistry PY - 2013 U6 - https://doi.org/10.1002/maco.201106433 SN - 0947-5117 SN - 1521-4176 VL - 64 IS - 7 SP - 578 EP - 584 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-28933 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -