ASTM B651-1983(2015) Standard Test Method for Measurement of Corrosion Sites in Nickel Plus Chromium or Copper Plus Nickel Plus Chromium Electroplated Surfaces with Double-Beam Int.pdf

1、Designation: B651 83 (Reapproved 2015)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 B651; the number immediately foll

2、owing 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method

3、 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 corr

4、osion 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 corro

5、sion 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 and d

6、etermine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B487 Test Method for Measurement of Metal and OxideCoating Thickness by Microscopical Examination ofCross Section3. Summary of Test Method3.1 The depths and diameter of corrosion pits or the

7、 widthsof corrosion crevices, and the number of pits per squaremillimetre or crevices per linear millimetre on a specimensurface, are determined using optical aids (magnifier,microscope, and interference microscope). The values arecompared to dimensions and numbers of corrosion sitesobtained from ot

8、her 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 corrosi

9、on 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 issubsta

10、ntially higher, a tendency for earlier failure by corrosionof basis metal is evident.5. Apparatus5.1 Double-Beam Interference Microscope (lateral magnifi-cation about 100), capable of producing, with white light, avisible group of interference fringes, and equipped with acalibrated fine focus and a

11、graduated bifilar (movable crosshair) eyepiece.5.2 Magnifier or Microscope (10 to 20), 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 500,equipped with a bifilar eyepiece, for

12、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 change the

13、surface of the corrosion sites. Scouringpowder may be used to remove insoluble corrosion products,organic solvent to remove road tar, water accompanied bygentle abrasion with a cloth to remove lightly adherent soil, etc.1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand

14、Inorganic Coatings and is the direct responsibility of Subcommittee B08.05 onDecorative Coatings.Current edition approved March 1, 2015. Published April 2015. Originallyapproved in 1978. Last previous edition approved in 2010 as B651 83 (2010).DOI: 10.1520/B0651-83R15.2For referenced ASTM standards,

15、 visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1942

16、8-2959. United States16.2 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 sel

17、ected for 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 carb

18、onate (Na2CO3).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

19、. Procedure for Determination of Average Number ofPits or Cracks7.1 Using the 10 to 20 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 isemp

20、loyed, use the 100 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 100 microscope enclosing a kn

21、ownarea 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 100microscope,

22、 whichever 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 ina25cm2area.7.1.3 For surfaces with more than about five cracks permillimetre, count the number of cracks on the surface imag

23、ethat cross a 100 microscope reticle line of known length.7.1.4 For a surface with fewer than about five cracks permillimetre, lightly scribe a straight line up to 50 mm long onthe specimen surface. Using a magnifier or, if necessary, a100 microscope, count the number of cracks in a knownlength of l

24、ine, 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 squaremillimetre, or the number of cracks as cracks per millimetre.Enter re

25、sult 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 w

26、idth 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)

27、 being 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 measureme

28、nt. 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 thevalue into Table 1. (Fine-focus knobs are generally calibrateddirectly in micrometres, necessita

29、ting 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 theTABLE 1 Measurements of Corrosion Pits and Cracks in Nickel Plus Chromium or Copper Plus Nickel Plus Chromium Plated SurfacesSAMP

30、LE 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 _ mPenetration of Crack or Pit into t

31、he 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 _ mB651 83 (2015)2sites. Then repeat the steps in 8.1 on ten pits or cracks.

32、 A 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 v

33、alues of “Thickness.” Employ a microscope havinga magnification capability of at least 500.NOTE 5For a guide to the procedure for measuring the thickness ofeach deposit consult Test Method B487.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 B487.10.4 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 of

42、 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 determi

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