A number in parentheses indicates the year of last reapproval. This standard has been approved for use by agencies of the U. Department of Defense. This will determine the suit-ability of the method for measuring the thickness of thincoatings.

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A number in parentheses indicates the year of last reapproval. This standard has been approved for use by agencies of the U. Department of Defense. This will determine the suit-ability of the method for measuring the thickness of thincoatings. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.

This is especiallyapplicable to the chemicals cited in Table X2. Referenced Documents2. Summary of Test Method3. The thickness of the cross section is measured with anoptical microscope. NOTE 1—These techniques will be familiar to experienced metallogra-phers but some guidance is given in Section 5 and in Appendix X1 for lessexperienced operators.

Significance and Use4. Factors Influencing the Measurement Result5. See X1. Edge rounding can be caused byimproper mounting, grinding, polishing, or etching.

It isusually minimized by overplating the test specimen beforemounting. Removal ofcoating material during surface preparation for overplating cancause a low-thickness measurement. Excessive etching produces a poorly defined or wide linewhich may result in an erroneous measurement. Current edition approved Dec. Published December Originallyapproved in Last previous edition approved in as B — 85 DOI: United States The apparent boundary may be poorlydefined or very irregular instead of straight and well defined.

To verify the absence of smearing, the coating thickness shouldbe measured and the polishing, etching, and thickness mea-surement repeated. A significant change in apparent thicknessindicates that smearing was probably present during one of themeasurements. If possible, the magnification should be chosen so that thefield of view is between 1. Errors of several percent are notunrealistic unless the scale has been calibrated or has beencertified by a responsible supplier. The distance between twolines of a stage micrometer used for the calibration shall beknown to within 0.

Ifa stage micrometer is not certified for accuracy, it should becalibrated. A generally satisfactory means of calibration is toassume that the stated length of the full scale is correct, tomeasure each subdivision with a filar micrometer, and tocalculate the length of each subdivision by simple proportion.

The measurement will be no more accurate than thecalibration of the eyepiece. As calibration is operatordependent, the eyepiece shall be calibrated by the personmaking the measurement. If the final motionduring alignment of the hairline is always made in the samedirection, this error will be eliminated.

Poor quality lensescould preclude accurate measurements. Sometimes imagesharpness can be improved by using monochromatic light. A change intube length may occur when the eyepiece is repositioned withinthe tube, when the focus of the eyepiece tube is changed, and,for some microscopes, when the fine focus is adjusted or theinterpupillary distance for binoculars is changed.

Preparation of Cross Sections6. Some typicaletchants are described in Appendix X2. Test Report8. Precision and Bias9. Under good conditions, whenusing an optical microscope, the method is capable of giving anabsolute measuring accuracy of 0. It is not reasonable to specify only one set oftechniques, and it is impractical to include all suitable tech-niques. The techniques described in this appendix are intendedas guidance for metallographers not experienced in measure-ments of coating thickness.

For additional guidance see Meth-ods E3. Forhard, brittle coatings for example oxide or chromium coat-ings tightly wrapping the specimen in soft aluminum foilbefore mounting has proved successful. It is better to overplate zinc with cadmium and viceversa. If, before grinding,reference marks are inscribed on the side of the mount, anyinclination from horizontal is easily measurable.

Initial grinding should employ or gradeabrasive to reveal the true specimen profile and to removedeformed metal. This may beminimized by totally immersing abrasive papers in a lubricantduring grinding or by using a copious flow of lubricant. Ifabrasive particles do become embedded, they may be removedby applying a short, light hand polish with metal polish aftergrinding and before diamond finishing or by one or morecycles of alternate etching and polishing. Some typical etchants are given in Appendix X2.

The latter has a lower precision. Animage-splitting eyepiece is advantageous for thin coatings onrough substrate surfaces. Measurement of the image projectedon to a ground-glass plate is usually less satisfactory because ofthe lack of sharpness of the image and poor legibility of theruler when the projected image is visible.


Corrosion Testing Standards

More B Such measurements have been used to evaluate the quality of seal of an anodic coating. The test method does not prescribe the procedure for producing the anodic coating, nor the postanodizing treatment usually described as "sealing. The interpretation of results and correlation of data with service experience and other tests are not within the scope of this test method. The impedance of anodic coatings is defined in terms of resistance and capacitive reactance.


ASTM B487 - 85(2013)







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