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"Ochrona przed Korozją" (Corrosion Protection) No. 02/2011

Application of novel investigations technique in zinc layer microstructure analysis
Wydział Inżynierii Materiałowej, Politechnika Warszawska
Common use and development of novel investigations technique is useful to get complementary information on zinc layers microstructure. Different techniques application, which are able to analyze materials microstructure in wide range of scale, give possibility to imaging all microstructure elements. That kind results are easier for interpretation of zinc layer growth mechanism. Zinc layer formation in hot-dip zinc galvanizing technique is growing too fast to analyze it, so most of results are present microstructure after layer formation. Classical approach to properties analysis of zinc layer is based on cross-section microstructure observations by application of light microscopy. This technique is useful for investigation of zinc layers complicated structure. Microstructure of different phases is revealed by chemical etching. However for complete characterization of the zinc layer microstructure, it is necessary to apply other techniques like Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), Focused Ion Beam (FIB). These techniques are more suitable for microstructure investigations in wide range of scale. Sophisticated phase analysis are also important during zinc layer investigations. That investigations are possible with synchrotron radiation. This paper contains description of different techniques and results which revealed zinc layer microstructure. Presented results can be used for novel approach on zinc layer composition.
Key words: hot-dip zinc galvanizing, zinc layer, zinc layer microstructure, electron microscopy
Controlling of corrosion resistance of magnesium alloys using hybrid method
Wydział Inżynierii Materiałowej,
Politechnika Warszawska
The small specific mass and advantageous properties, make magnesium alloys attractive constructional and functional materials. There is however an important obstacle to their wider use, namely their poor resistance to corrosion and frictional wear, while no surface treatments are available which would effectively prolong their service life. A prospective solution is to produce diffusion chromium nitride or titanium nitride composite layers on the surface of these alloys using a hybrid treatment in which, the alloy surface is pre-coated with a chromium or titanium layer and then subjected to glow discharge assisted nitriding. Thanks to their diffusion character, the layers thus obtained increase the resistance of the alloy to corrosion and frictional wear. The paper presents the results of the investigations, which determines the effect of the various variants of the diffusion chromium and titanium nitride surface layers on the corrosion resistance of magnesium alloys.
Key words: magnesium alloys, chromium nitride and titanium nitride layers, hybrid method, microstructure, corrosion and wear resistance
The influence of grain size on the corrosion resistance of 7475 aluminium alloy
Wydział Inżynierii Materiałowej, Politechnika Warszawska
In this study, the corrosion resistance of 7475 aluminium alloy with nano- and micrograin size and various precipitates was investigated in 0.1M NaCl. The potentiodynamic polarization measurements showed that nanocrystalline samples have a lower corrosion potential and lower corrosion current compared to microcrystalline one. The observations of surface morphology revealed the galvanic corrosion related to the presence of intermetallic particles. For microcrystalline sample, the intergranular corrosion attack was observed.
Key words:aluminium alloys, grain size, pitting corrosion
Corrosion resistance of nickel/carbon nanotubes (Ni/CNTs) nanocomposite layers produced by electrochemical method
Wydział Inżynierii Materiałowej, Politechnika Warszawska
The paper is focused on presentations of examination results of corrosion properties of nanocomposite Ni/CNTs layers produced by electrochemical method. For comparison purposes the nanocrystaline nickel layers were also examined. Characteristics of disperse phase and structures of Ni/CNTs and Ni layers are presented. Corrosion examinations were realized by the methods: potentiodynamic and electrochemical impedance spectroscopy (EIS) in 0.5M solution of NaCl. Polarization characteristics j = f(E) and corrosion parameters jcor and Ecor of the studied materials are determined. Spectral characteristics in the forms of the Nyquist and Bode plots and the corresponding electrical circuits of the studied corrosion systems are established by applying the EIS method. An estimation of the material destruction after corrosion examinations is obtained by using the scanning electron microscopy approach.
Key words: nanocrystalline Ni layers, nanocomposite Ni/CNTs layers, carbon nanotubes CNTs, corrosuion resistance
Corrosion resistance of sintered austenitic stainless steel aisi 316L after active screen glow-discharge nitriding
Wydział Inżynierii Materiałowej, Politechnika Warszawska
Instytut Mechaniki Precyzyjnej, Warszawa
Instytut Inżynierii Materiałowej, Politechnika Krakowska
Wydział Inżynierii Materiałowej, Politechnika Warszawska
The paper presents comparative results of examinations of microstructure and properties of the nitrided layers produced on sintered 316L austenitic stainless steel by low-temperature glow-discharge assisted nitriding with the samples placed on the cathode or in the plasma region (active screen glow-discharge nitriding). It has been shown that in this process a change of the polarization parameters affects essentially the thickness, surface topography, chemical composition, and phase composition of the nitrided layers produced on the sintered 316L steel samples, thereby affecting their wear resistance and corrosion resistance. The low-temperature glow-discharge nitriding of sintered 316L steel samples, irrespective of whether placed on the cathode or in the plasma region, appeared to increase significantly the wear resistance and the corrosion resistance.
Key words: austenitic stainless steel, sintered austenitic stainless steel, glow-discharge nitriding, S phase, wear resistance, corrosion resistance