ASTM B651-83(1995)

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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Designation: B 651 – 83 (Reapproved 1995)
Standard Test Method for
Measurement of Corrosion Sites in Nickel Plus Chromium
or Copper Plus Nickel Plus Chromium Electroplated
Surfaces with Double-Beam Interference Microscope
This standard is issued under the fixed designation B 651; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope the same conditions for the same length of time. Differences in
the average values of the radius or half-width or of penetration
1.1 This test method provides a means for measuring the
into an underlying metal layer are significant measures of the
average dimensions and number of corrosion sites in an
relative corrosion resistance of the systems. Thus, if the pit
electroplated decorative nickel plus chromium or copper plus
radii are substantially higher on samples with a given electro-
nickel plus chromium coating on steel after the coating has
plating system, when compared to other systems, a tendency
been subjected to corrosion tests. This test method is useful for
for earlier failure of the former by formation of visible pits is
comparing the relative corrosion resistances of different elec-
indicated. If penetration into the semi-bright nickel layer is
troplating systems and for comparing the relative corrosivities
substantially higher, a tendency for earlier failure by corrosion
of different corrosive environments. The numbers and sizes of
of basis metal is evident.
corrosion sites are related to deterioration of appearance.
Penetration of the electroplated coatings leads to appearance of
5. Apparatus
basis metal corrosion products.
5.1 Double-Beam Interference Microscope (lateral magni-
1.2 The values stated in SI units are to be regarded as the
fication about 1003), capable of producing, with white light, a
standard.
visible group of interference fringes, and equipped with a
1.3 This standard does not purport to address all of the
calibrated fine focus and a graduated bifilar (movable cross
safety concerns, if any, associated with its use. It is the
hair) eyepiece.
responsibility of the user of this standard to establish appro-
5.2 Magnifier or Microscope (103 to 203), with light
priate safety and health practices and determine the applica-
source.
bility of regulatory limitations prior to use.
5.3 Rule, graduated in millimetres, and a scriber for pro-
2. Referenced Documents ducing visible lines on the specimen surface.
5.4 Microscope, with a magnification capability of 5003,
2.1 ASTM Standards:
equipped with a bifilar eyepiece, for making measurements on
B 487 Test Method for Measurement of Metal and Oxide
opaque surfaces.
Coating Thickness by Microscopical Examination of a
5.5 Equipment for mounting and polishing of specimens for
Cross Section
microscopical cross-sectional measurements.
3. Summary of Test Method
6. Specimen Preparation
3.1 The depths and diameter of corrosion pits or the widths
6.1 Clean the corroded specimen surface with an agent or
of corrosion crevices, and the number of pits per square
agents that remove soil and corrosion products, but do not
millimetre or crevices per linear millimetre on a specimen
significantly change the surface of the corrosion sites. Scouring
surface, are determined using optical aids (magnifier, micro-
powder may be used to remove insoluble corrosion products,
scope, and interference microscope). The values are compared
organic solvent to remove road tar, water accompanied by
to dimensions and numbers of corrosion sites obtained from
gentle abrasion with a cloth to remove lightly adherent soil, etc.
other specimens.
6.2 Mask with paint or tape that portion of the specimen
4. Significance and Use surface on which no measurements of pits or cracks will be
made. Alternatively, a gasketed cell pressed onto the surface
4.1 Different electroplating systems can be corroded under
may be used. The opening in the gasket will define the area to
be stripped.
This test method is under the jurisdiction of ASTM Committee B-8 on Metallic
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.08.03
NOTE 1—If pitted, the area selected for measurement should contain at
on Decorative Coatings.
least 100 pits or be as large as 50 by 50 mm. If the area contains cracks,
Current edition approved August 26, 1983. Published December 1983. Originally
the location for measurement should contain at least 100 cracks, or be at
published as B 651 – 78. Last previous edition B 651 – 78.
least 50 mm long.
Annual Book of ASTM Standards, Vol 02.05.
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B 651
perpendicular to the predominant crack direction.
6.3 Strip the chromium anodically at 6 to 8 V in a solution
containing about 50 g/L of sodium carbonate (Na CO ).
2 3 7.2 Calculate the number of pits as pits per square millime-
6.4 Remove masking material, if desired.
tre, or the number of cracks as cracks per millimetre. Enter
result in Table 1 under “pit density” or “crack density.”
NOTE 2—If tape was employed for masking, its removal is recom-
mended. When the specimen rests on tape, it will allow the specimen to
8. Determination of Mean Dimensions of Pits or Cracks
settle slowly. This gradual movement interferes with measurements of
penetration with the interference microscope. 8.1 Observe one pit or crack with the interference micro-
scope.
7. Procedure for Determination of Average Number of
8.1.1 Using the bifilar eyepiece, count the number of eye-
Pits or Cracks
piece scale units occupied by the major diameter of the pit, or
7.1 Using the 103 to 203 magnifier, count the number of
by the width of the crack. If the crack width varies, or if the pit
pits in a known area or the number of cracks intersecting a line outline is irregular, estimate the average. Enter “width” value
of known length. Where uncertainty exists as to whether
in Table 1.
localized blemishes are corrosion sites when the magnifier is 8.1.2 Adjust the elevation of the microscope tube so that
employed, use the 1003 microscope for verification. Extreme
interference fringes appear in the deepest part of the pit or the
accuracy is not necessary; values within 6 10 % of the true crack (the portion seen in the field of view) being measured;
value are adequate.
enter the reading on fine-focus knob under B in Table 1. Using
7.1.1 For surfaces where the number of pits is more than the fine-focus knob only, raise the tube so that the fringes
about 1000/cm , count the pits bounded by lines seen in the
appear on the uncorroded surface surrounding the corroded
eyepiece reticle of the 1003 microscope enclosing a k
...