The Corrosion Behavior of Sputter-Deposited Nanocrystalline W-Cr Alloys in Nacl and NaohaSolutions

Abstract

The corrosion behavior of the sputter-deposited nanocrystalline W-Cr alloys was
studied in 0.5 M NaCl and alkaline 1 M NaOH solutions at 25°C, open to air using
immersion tests and electrochemical measurements. Chromium metal acts synergistically
with tungsten in enhancing the corrosion resistance of the sputter-deposited W-Cr alloys so
as to show higher corrosion resistance than those of alloy-constituting elements in both 0.5
M NaCl and 1 M NaOH solutions. In particular, the nanocrystalline W-Cr alloys containing
25-91 at% chromium showed about one order of magnitude lower corrosion rates (that is,
about 1-2 × 10^-3 mm.y^-1) than those of tungsten and chromium metals even for prolonged
immersion in 0.5 M NaCl solution at 25°C. On the other hand, the corrosion rate of the
sputter-deposited W-Cr alloys containing 25-75 at % chromium was decreased significantly
with increasing chromium content and showed lowest corrosion rates (that is, 1.5-2.0 × 10^-3 mm.y^-1) after immersed for prolonged immersion in 1 M NaOH solution. The corrosion rates
of these nanocrystalline W-(25-75)Cr alloys are nearly two orders of magnitude lower than
that of tungsten and more than one order of magnitude lower corrosion rate than that of
sputter-deposited chromium metal in 1 M NaOH solution. The corrosion-resistant of all the
examined sputter-deposited W-Cr alloys in 0.5 M NaCl solution is higher than in alkaline 1
M NaOH solution at 25°C. Open circuit potentials of all the examined W-Cr alloys are
shifted to more noble direction with increasing the chromium content in the alloys after
immersion for 72 h in both 0.5 M NaCl and 1 M NaOH solutions at 25°C, open to air.

Keywords: Sputter deposition, nanocrystalline W-Cr alloys, corrosion test, electrochemical
measurement, NaCl and NaOH solutions.

DOI:  10.3126/jncs.v25i0.3300

Journal of Nepal Chemical Society Volume 25, 2010 pp 53-61