1、Designation: B 651 83 (Reapproved 2006)Standard Test Method forMeasurement of Corrosion Sites in Nickel Plus Chromiumor Copper Plus Nickel Plus Chromium ElectroplatedSurfaces with Double-Beam Interference Microscope1This standard is issued under the fixed designation B 651; the number immediately fo
2、llowing the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test met
3、hod provides a means for measuring theaverage dimensions and number of corrosion sites in anelectroplated decorative nickel plus chromium or copper plusnickel plus chromium coating on steel after the coating hasbeen subjected to corrosion tests. This test method is useful forcomparing the relative c
4、orrosion resistances of different elec-troplating systems and for comparing the relative corrosivitiesof different corrosive environments. The numbers and sizes ofcorrosion sites are related to deterioration of appearance.Penetration of the electroplated coatings leads to appearance ofbasis metal co
5、rrosion products.1.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices an
6、d determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B 487 Test Method for Measurement of Metal and OxideCoating Thickness by Microscopical Examination of aCross Section3. Summary of Test Method3.1 The depths and diameter of corrosion pits
7、or the widthsof corrosion crevices, and the number of pits per squaremillimetre or crevices per linear millimetre on a specimensurface, are determined using optical aids (magnifier, micro-scope, and interference microscope). The values are comparedto dimensions and numbers of corrosion sites obtaine
8、d fromother specimens.4. Significance and Use4.1 Different electroplating systems can be corroded underthe same conditions for the same length of time. Differences inthe average values of the radius or half-width or of penetrationinto an underlying metal layer are significant measures of therelative
9、 corrosion resistance of the systems. Thus, if the pitradii are substantially higher on samples with a given electro-plating system, when compared to other systems, a tendencyfor earlier failure of the former by formation of visible pits isindicated. If penetration into the semi-bright nickel layer
10、issubstantially higher, a tendency for earlier failure by corrosionof basis metal is evident.5. Apparatus5.1 Double-Beam Interference Microscope (lateral magni-fication about 1003), capable of producing, with white light, avisible group of interference fringes, and equipped with acalibrated fine foc
11、us and a graduated bifilar (movable crosshair) eyepiece.5.2 Magnifier or Microscope (103 to 203), with lightsource.5.3 Rule, graduated in millimetres, and a scriber for pro-ducing visible lines on the specimen surface.5.4 Microscope, with a magnification capability of 5003,equipped with a bifilar ey
12、epiece, for making measurements onopaque surfaces.5.5 Equipment for mounting and polishing of specimens formicroscopical cross-sectional measurements.6. Specimen Preparation6.1 Clean the corroded specimen surface with an agent oragents that remove soil and corrosion products, but do notsignificantly
13、 change the surface of the corrosion sites. Scouringpowder may be used to remove insoluble corrosion products,1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.08.03on Decorative Coatings.Current ed
14、ition approved April 1, 2006. Published April 2006. Originallyapproved in 1978. Last previous edition approved in 2001 as B 651 83 (2001).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
15、information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.organic solvent to remove road tar, water accompanied bygentle abrasion with a cloth to remove lightly adher
16、ent soil, etc.6.2 Mask with paint or tape that portion of the specimensurface on which no measurements of pits or cracks will bemade. Alternatively, a gasketed cell pressed onto the surfacemay be used. The opening in the gasket will define the area tobe stripped.NOTE 1If pitted, the area selected fo
17、r measurement should contain atleast 100 pits or be as large as 50 by 50 mm. If the area contains cracks,the location for measurement should contain at least 100 cracks, or be atleast 50 mm long.6.3 Strip the chromium anodically at 6 to 8 V in a solutioncontaining about 50 g/L of sodium carbonate (N
18、a2CO3).6.4 Remove masking material, if desired.NOTE 2If tape was employed for masking, its removal is recom-mended. When the specimen rests on tape, it will allow the specimen tosettle slowly. This gradual movement interferes with measurements ofpenetration with the interference microscope.7. Proced
19、ure for Determination of Average Number ofPits or Cracks7.1 Using the 103 to 203 magnifier, count the number ofpits in a known area or the number of cracks intersecting a lineof known length. Where uncertainty exists as to whetherlocalized blemishes are corrosion sites when the magnifier isemployed,
20、 use the 1003 microscope for verification. Extremeaccuracy is not necessary; values within 610 % of the truevalue are adequate.7.1.1 For surfaces where the number of pits is more thanabout 1000/cm2, count the pits bounded by lines seen in theeyepiece reticle of the 1003 microscope enclosing a knowna
21、rea of specimen surface (probably about 0.5 mm2).7.1.2 For surfaces where the number of pits is less thanabout 1000/cm2, lightly scribe lines 10 mm or less apart toform a rectilinear grid on the surface. Count the number of pitswithin a scribed area, by using the magnifier, or the 1003microscope, wh
22、ichever has the necessary resolution to assurepit identification. Determine the area that contains about 100pits, or, if the area exceeds 25 cm2, count the number of pits ina 25-cm2area.7.1.3 For surfaces with more than about 5 cracks permillimetre, count the number of cracks on the surface imagetha
23、t cross a 1003 microscope reticle line of known length.7.1.4 For a surface with fewer than about 5 cracks permillimetre, lightly scribe a straight line up to 50 mm long onthe specimen surface. Using a magnifier or, if necessary, a1003 microscope, count the number of cracks in a knownlength of line,
24、or all the cracks in 50-mm length, whichevercomes first.NOTE 3If the cracks tend to be oriented, scribe the line approximatelyperpendicular to the predominant crack direction.7.2 Calculate the number of pits as pits per square millime-tre, or the number of cracks as cracks per millimetre. Enterresul
25、t in Table 1 under “pit density” or “crack density.”8. Determination of Mean Dimensions of Pits or Cracks8.1 Observe one pit or crack with the interference micro-scope.8.1.1 Using the bifilar eyepiece, count the number of eye-piece scale units occupied by the major diameter of the pit, orby the widt
26、h of the crack. If the crack width varies, or if the pitoutline is irregular, estimate the average. Enter “width” valuein Table 1.8.1.2 Adjust the elevation of the microscope tube so thatinterference fringes appear in the deepest part of the pit or thecrack (the portion seen in the field of view) be
27、ing measured;enter the reading on fine-focus knob under B in Table 1. Usingthe fine-focus knob only, raise the tube so that the fringesappear on the uncorroded surface surrounding the corrodedsite, and so that the center of the fringe group is aligned withthe location of the penetration measurement.
28、 The best fringeorientation is perpendicular to the major pit diameter or crackdirection. Enter the reading on fine-focus knob under A inTable 1. Subtract B from A to obtain penetration P and enter theTABLE 1 Measurements of Corrosion Pits and Cracks in Nickel Plus Chromium or Copper Plus Nickel Plu
29、s Chromium Plated SurfacesSAMPLE NO. _ EXPOSURE MEDIUM _ EXPOSURE TIME _Pit or crack density (7.2) _ pits/mm2_ cracks/mm2Pit or crack dimensions (8.1.1) pit diameter _ mcrack width _ mThicknesses of deposits (8.2) copper _ msemibright nickel _ mbright nickel _ mother nickel layer _ mchromium _ mPene
30、tration of Crack or Pit into the Semibright Nickel or Copper LayersTotal Penetration (P)(8.1.2)Penetration into Semibright Nickel(8.3)Penetration into Copper (8.4)A _ m _ m _ mB _ mA-B _ m mean penetration into semibright mean penetration into copper_ m _ mB 651 83 (2006)2value into Table 1. (Fine-f
31、ocus knobs are generally calibrateddirectly in micrometres, necessitating no further conversion.)NOTE 4If the bottoms of the corrosion sites do not produce visiblefringes, treat the specimen with a suitable agent to clean or to brighten thesites. Then repeat the steps in 8.1 on ten pits or cracks. A
32、 15-s soak in awater solution of 5 % H2SO4, by weight, followed immediately with awater rinse, is often helpful.8.2 Section the specimen in the location of the abovemeasurements. Mount, polish, etch, and measure (Note 5) thethickness of each deposit; enter the values into Table 1 underrespective val
33、ues of “Thickness.” Employ a microscope havinga magnification capability of at least 5003.NOTE 5For a guide to the procedure for measuring the thickness ofeach deposit consult Test Method B 487.NOTE 6A suggested etchant is 1 part by volume glacial acetic acid, 1part concentrated nitric acid, (sp gr
34、1.42) and 1 part glycerin.Approximateetch time is 30 s.8.3 For the determination of penetration by corrosion intothe semi-bright nickel layer, subtract the value of thickness ofall deposits above the semi-bright layer (obtained in 8.2) fromeach value of penetration P (obtained in 8.1.2); enter eachv
35、alue of penetration into Table 1 into the column designated “semi-bright penetration.” Calculate the arithmetic mean of thevalues and enter the “Mean Penetration,” Psinto Table 1.8.4 For determination of penetration into the copper layer,subtract the thickness of all the layers above copper from the
36、 1penetration value (A B)inTable 1. Calculate the arithmeticmean of the differences, and enter “Mean Penetration,” PcuintoTable 1.9. Report9.1 Report the following information:9.1.1 Sample number or identification,9.1.2 Exposure medium,9.1.3 Exposure time,9.1.4 Thickness of deposits,9.1.5 Pit or cra
37、ck density,9.1.6 Pit or crack dimensions: width and penetration,NOTE 7Level A (Table 1) is the reading on the calibrated fine-focusknob corresponding to the specimen surface plane. Level B is the readingon the calibrated fine-focus knob corresponding to the maximum depth ofthe pit or crack. ABis the
38、 depth of the pit or crack.9.1.7 Semi-bright penetration, and9.1.8 Copper penetration.10. Precision and Bias10.1 Precision of individual penetration measurements canbe as good as 61 m. It is determined by the care with whichthe interference fringes, which move laterally across the fieldof view as th
39、e focus knob is turned, are positioned (either in thecorrosion site or on the top surface).10.2 Bias of individual penetration measurements can be asgood as the precision, since the method has no built-in bias; itcan be even better than the precision when computed as astatistical average. Bias is de
40、termined by the precision and bythe care with which the pits are cleaned of foreign material buthave had no metal removed by etching of any cleaning agent.10.3 Bias of individual pit diameter measurements andthickness measurements can be as good as 61 m. Suggestionsfor obtaining measurements of best
41、 bias are found in TestMethod B 487.10.4 Biases of the means obtained for penetration, sitediameter or width, and number are determined by the unifor-mity of distribution of pit size and density across the surfaceand by the number of individual pits measured that are used toobtain the mean. Values o
42、f number and size of corrosion sitesneed not be more accurate than 610 % of the true averagevalue.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determ
43、ination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or w
44、ithdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that
45、your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).B 651 83 (2006)3
