ASTM B651-83(2001)
(Test Method)Standard Test Method for Measurement of Corrosion Sites in Nickel Plus Chromium or Copper Plus Nickel Plus Chromium Electroplated Surfaces with the Double-Beam Interference Microscope
Standard Test Method for Measurement of Corrosion Sites in Nickel Plus Chromium or Copper Plus Nickel Plus Chromium Electroplated Surfaces with the Double-Beam Interference Microscope
SCOPE
1.1 This method provides a means for measuring the average dimensions and number of corrosion sites in an electroplated decorative nickel plus chromium or copper plus nickel plus chromium coating on steel after the coating has been subjected to corrosion tests. The method is useful for comparing the relative corrosion resistances of different electroplating systems and for comparing the relative corrosivities of different corrosive environments. The numbers and sizes of corrosion sites are related to deterioration of appearance. Penetration of the electroplated coatings leads to appearance of basis metal corrosion products.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:B651–83 (Reapproved 2001)
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 B651; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Significance and Use
1.1 This test method provides a means for measuring the 4.1 Different electroplating systems can be corroded under
average dimensions and number of corrosion sites in an the same conditions for the same length of time. Differences in
electroplated decorative nickel plus chromium or copper plus the average values of the radius or half-width or of penetration
nickel plus chromium coating on steel after the coating has into an underlying metal layer are significant measures of the
beensubjectedtocorrosiontests.Thistestmethodisusefulfor relative corrosion resistance of the systems. Thus, if the pit
comparing the relative corrosion resistances of different elec- radii are substantially higher on samples with a given electro-
troplating systems and for comparing the relative corrosivities plating system, when compared to other systems, a tendency
of different corrosive environments. The numbers and sizes of for earlier failure of the former by formation of visible pits is
corrosion sites are related to deterioration of appearance. indicated. If penetration into the semi-bright nickel layer is
Penetrationoftheelectroplatedcoatingsleadstoappearanceof substantially higher, a tendency for earlier failure by corrosion
basis metal corrosion products. of basis metal is evident.
1.2 The values stated in SI units are to be regarded as the
5. Apparatus
standard.
5.1 Double-Beam Interference Microscope (lateral magni-
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the fication about 1003), capable of producing, with white light, a
visible group of interference fringes, and equipped with a
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- calibrated fine focus and a graduated bifilar (movable cross
bility of regulatory limitations prior to use. hair) eyepiece.
5.2 Magnifier or Microscope (103 to 203), with light
2. Referenced Documents
source.
2.1 ASTM Standards: 5.3 Rule, graduated in millimetres, and a scriber for pro-
B487 Test Method for Measurement of Metal and Oxide ducing visible lines on the specimen surface.
Coating Thickness by Microscopical Examination of a 5.4 Microscope, with a magnification capability of 5003,
Cross Section equipped with a bifilar eyepiece, for making measurements on
opaque surfaces.
3. Summary of Test Method
5.5 Equipmentformountingandpolishingofspecimensfor
3.1 The depths and diameter of corrosion pits or the widths microscopical cross-sectional measurements.
of corrosion crevices, and the number of pits per square
6. Specimen Preparation
millimetre or crevices per linear millimetre on a specimen
surface, are determined using optical aids (magnifier, micro- 6.1 Clean the corroded specimen surface with an agent or
scope, and interference microscope). The values are compared agents that remove soil and corrosion products, but do not
to dimensions and numbers of corrosion sites obtained from significantlychangethesurfaceofthecorrosionsites.Scouring
other specimens. powder may be used to remove insoluble corrosion products,
organic solvent to remove road tar, water accompanied by
gentleabrasionwithaclothtoremovelightlyadherentsoil,etc.
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.08.03
on Decorative Coatings.
CurrenteditionapprovedAugust26,1983.PublishedDecember1983.Originally
published as B651–78. Last previous edition B651–78.
Annual Book of ASTM Standards, Vol 02.05.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B651
6.2 Mask with paint or tape that portion of the specimen 7.1.3 For surfaces with more than about 5 cracks per
surface on which no measurements of pits or cracks will be millimetre, count the number of cracks on the surface image
made. Alternatively, a gasketed cell pressed onto the surface that cross a 1003 microscope reticle line of known length.
may be used. The opening in the gasket will define the area to 7.1.4 For a surface with fewer than about 5 cracks per
be stripped. millimetre, lightly scribe a straight line up to 50 mm long on
the specimen surface. Using a magnifier or, if necessary, a
NOTE 1—If pitted, the area selected for measurement should contain at
1003 microscope, count the number of cracks in a known
least 100 pits or be as large as 50 by 50 mm. If the area contains cracks,
length of line, or all the cracks in 50-mm length, whichever
the location for measurement should contain at least 100 cracks, or be at
comes first.
least 50 mm long.
6.3 Strip the chromium anodically at 6 to 8 V in a solution
NOTE 3—Ifthecrackstendtobeoriented,scribethelineapproximately
containing about 50 g/L of sodium carbonate (Na CO ). perpendicular to the predominant crack direction.
2 3
6.4 Remove masking material, if desired.
7.2 Calculate the number of pits as pits per square millime-
tre, or the number of cracks as cracks per millimetre. Enter
NOTE 2—If tape was employed for masking, its removal is recom-
result in Table 1 under “pit density” or “crack density.”
mended. When the specimen rests on tape, it will allow the specimen to
settle slowly. This gradual movement interferes with measurements of
penetration with the interference microscope.
8. Determination of Mean Dimensions of Pits or Cracks
8.1 Observe one pit or crack with the interference micro-
7. Procedure for Determination of Average Number of
scope.
Pits or Cracks
8.1.1 Using the bifilar eyepiece, count the number of eye-
7.1 Using the 103 to 203 magnifier, count the number of
piece scale units occupied by the major diameter of the pit, or
pitsinaknownareaorthenumberofcracksintersectingaline
bythewidthofthecrack.Ifthecrackwidthvaries,orifthepit
of known length. Where uncertainty exists as to whether
outline is irregular, estimate the average. Enter “width” value
localized blemishes are corrosion sites when the magnifier is
in Table 1.
employed, use the 1003 microscope for verification. Extreme
8.1.2 Adjust the elevation of the microscope tube so t
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