TY - JOUR A1 - Rosemann, P. A1 - Schmidt, J. A1 - Heyn, Andreas T1 - Short and long term degradation behaviour of Mg-1Ca magnesium alloys and protective coatings based on plasma-chemical oxidation and biodegradable polymer coating in synthetic body fluid N2 - The main problem limiting the application of magnesium alloys as biodegradable implant material is its high degradation rate. In order to slow down the corrosion rate an extrusion process and specific coating systems based on plasma-chemical oxidation (PCO) and organic dip coating with poly(ʟ-lactid-co-caprolacton) (PLLC) were applied on Mg–1Ca magnesium alloy. The additional PLLC coating is used to delay the start of substrate corrosion, while the purpose of the PCO coating is to decrease the substrate corrosion rate. The corrosion behaviour was investigated in synthetic body fluid (SBF) through measurement of the hydrogen evolution rate in long term tests and polarisation and electrochemical noise measurements in short term tests. The results showed significant differences between the cast and extruded alloys and a decrease of the corrosion rate due to corrosion product formation. The combination of both coating systems resulted in a significant delay of metal substrate corrosion and all coating systems showed good correlation between short and long term tests. The combination of the three investigation methods provides the possibility to gain more information about the degradation behaviour and break down of protective coatings. KW - Coatings KW - Corrosion KW - Electrochemical noise KW - Magnesium KW - Plasma-chemical oxidation PY - 2013 U6 - https://doi.org/10.1002/maco.201206590 SN - 0947-5117 SN - 1521-4176 VL - 64 IS - 8 SP - 714 EP - 722 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-29074 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bender, S. A1 - Holzhausen, U. A1 - Heyn, Andreas T1 - Investigations of the aqueous corrosion of pretreated magnesium alloys by means of electrochemical noise measurements N2 - An important possibility to improve the corrosion behaviour of magnesium alloys is the application of protective coatings. The quality of such coatings depends mainly on the pretreatment and the exposure conditions after pretreatment. Since magnesium surfaces change much faster under atmospheric conditions than those of almost any other technical material, it is necessary to pay special attention to this particular feature. The activity of acid-pickled surfaces of the magnesium alloys AZ31 and AZ91 in dependence on the exposure time and the humidity conditions was investigated with electrochemical noise (EN) measurements. In addition to pickling, plasma chemical vapour deposition processes open new possibilities for an economical, as well as ecologically quite safe, pretreatment. The results of EN investigations after acid pickling as well as specific plasma oxidation treatments of the two magnesium alloys after exposure to air with different humidities are presented. KW - Corrosion KW - CVD KW - Electrochemical noise KW - Magnesium alloys KW - Pretreatment PY - 2013 U6 - https://doi.org/10.1002/maco.201206741 SN - 0947-5117 SN - 1521-4176 VL - 64 IS - 8 SP - 708 EP - 713 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-29073 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 - Sarmiento Klapper, Helmuth A1 - Heyn, Andreas A1 - Burkert, Andreas A1 - Göllner, J. T1 - The effect of passive layer stability on electrochemical noise signals arising from pitting corrosion of stainless steels N2 - Electrochemical noise (EN) enables corrosion research and monitoring in real time and with high sensitivity. In the case of submicroscopic nucleation events of pitting corrosion it has been observed that the cathodic process plays a decisive role in the mechanism as well as in the origin of EN signals, which depend not only on the metallic dissolution reaction but also on the electron-consuming process. EN signals arising from the nucleation process of localized corrosion on stainless steels can only be recorded due to the inhibition effect on the cathodic process achieved by the spontaneous formation of the passive layer. In consequence, passive layer stability becomes a significant factor in influencing EN signals. The way in which the passive layer stability affects the acquisition and analysis of EN signals arising from pitting corrosion on stainless steels is discussed in detail. KW - Cathodic reaction KW - Electrochemical noise KW - Pitting corrosion KW - Stainless steel PY - 2013 U6 - https://doi.org/10.1002/maco.201206739 SN - 0947-5117 SN - 1521-4176 VL - 64 IS - 8 SP - 671 EP - 674 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-29071 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Burkert, Andreas A1 - Klapper, H.S. A1 - Lehmann, Jens T1 - Novel strategies for assessing the pitting corrosion resistance of stainless steel surfaces N2 - Pitting corrosion is one of the most common mechanisms of surface damage on stainless steels. Electrochemical methods have been preferentially applied for the evaluation of the pitting corrosion resistance of stainless steels in the laboratory. Nevertheless, some of them are not reliable enough and in general the application of electrochemical methods in the field becomes difficult because of required deep understanding of corrosive phenomena and measurement technology. Therefore, new approaches for the evaluation of the pitting corrosion susceptibility of stainless steel surfaces in the laboratory as well as in the field are necessary. In the present paper two novel strategies including electrochemical noise measurements under anodic polarization for laboratory testing, and an indicator test to assess the susceptibility of stainless steel surfaces to pitting corrosion in the field are introduced. Experimental results concerning the influence of surface treatments on the pitting corrosion resistance on stainless steels have confirmed that final surface condition has a significant effect on their future pitting corrosion susceptibility. In addition, the pitting corrosion resistance of stainless steel surfaces was observed being specifically dependent on the achieved surface topography and in some cases independent on the roughness parameters of the surface. KW - Electrochemical noise KW - Pitting corrosion KW - Stainless steel KW - Surface treatments PY - 2013 U6 - https://doi.org/10.1002/maco.201206749 SN - 0947-5117 SN - 1521-4176 VL - 64 IS - 8 SP - 675 EP - 682 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-29011 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -