Effects of compositional and structural features on corrosion behavior of nickel–tungsten alloys |
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Authors: | Andrzej Królikowski Ewelina Płońska Andrzej Ostrowski Mikołaj Donten Zbigniew Stojek |
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Institution: | (1) Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland;(2) Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland |
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Abstract: | Ni–W alloys were electrodeposited onto copper foil from citrate solution. Coatings containing from 11 to 21 at.% W and having
7–52 μm in thickness were obtained. The structure of these alloys was analyzed by X-ray diffraction and by using electron
and light microscopy techniques. Alloys with 11 and 15% W are composed of two phases: solid solution of W in fcc Ni and solid
solution of Ni in bcc W. An increase in W content in the Ni–W alloys to ca. 18–19% of W resulted in the grain refinement and
the transition to amorphous structure. The corrosion behavior of obtained Ni–W and unalloyed Ni coatings was studied in 0.5 M
NaCl solution by means of electrochemical impedance spectroscopy, potentiodynamic polarization and light microscopy. Comparing
to pure Ni, the obtained Ni–W coatings exhibited a clearly decreased corrosion resistance (in terms of corrosion current density
and polarization or charge transfer resistance at the open circuit potential). Despite of the quite wide range of composition
of the alloys under test, the related grain refinement, and the transition to the amorphous structure, no clear relation between
the corrosion rate and W content was detected. This behavior can be a result of the interplay of the activating effect of
grain refinement or preferential dissolution of W from one side and diffusion barrier action or inhibition provided by the
surface film of W oxidation products from the other side. The differences observed in the corrosion resistance of Ni–W coatings
are more related to their morphological imperfections arising from various deposition conditions than to the W content. Some
samples showed a rather non-uniform nature of corrosion (pronounced attack along cracks). An inversion in the dissolution
behavior of Ni–W and unalloyed Ni was observed with increasing anodic potential. Contrary to pure Ni, Ni–W coatings were resistant
to pitting corrosion in NaCl solution.
Contribution to the Fall Meeting of the European Materials Research Society, Symposium D: 9th International Symposium on Electrochemical/Chemical
Reactivity of Metastable Materials, Warsaw, 17th–21st September, 2007. |
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Keywords: | Ni– W alloys Coatings Electrodeposition Corrosion resistance Structure |
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