Active Standard ASTM B765 | Developed by Subcommittee: B08.10
Book of Standards Volume: 02.05
Historical (view previous versions of standard)
Significance and Use
Porosity tests indicate the completeness of protection or coverage offered by the coating. When a given coating is known to be protective when properly deposited, the porosity serves as a measure of the control of the process. The effects of substrate finish and preparation, plating bath, coating process, and handling, may all affect the degree of imperfection that is measured.
Note 1—The substrate exposed by the pores may be the basis metal, an underplate, or both.
The tests in this guide involve corrosion reactions in which the products delineate pores in coatings. Since the chemistry and properties of these products may not resemble those found in service environments, these tests are not recommended for prediction of product performance unless correlation is first established with service experience.
1.1 This guide describes some of the available standard methods for the detection, identification, and measurement of porosity and gross defects in electrodeposited and related metallic coatings and provides some laboratory-type evaluations and acceptances. Some applications of the test methods are tabulated in Table 1 and Table 2.
1.2 This guide does not apply to coatings that are produced by thermal spraying, ion bombardment, sputtering, and other similar techniques where the coatings are applied in the form of discrete particles impacting on the substrate.
1.3 This guide does not apply to beneficial or controlled porosity, such as that present in microdiscontinuous chromium coatings.
1.4 Porosity test results (including those for gross defects) occur as chemical reaction end products. Some occur in situ, others on paper, or in a gel coating. Observations are made that are consistent with the test method, the items being tested, and the requirements of the purchaser. These may be visual inspection (unaided eye) or by 10× magnification (microscope). Other methods may involve enlarged photographs or photomicrographs.
1.5 The test methods are only summarized. The individual standards must be referred to for the instructions on how to perform the tests.
1.6 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
B276 Test Method for Apparent Porosity in Cemented Carbides
B374 Terminology Relating to Electroplating
B537 Practice for Rating of Electroplated Panels Subjected to Atmospheric Exposure
B542 Terminology Relating to Electrical Contacts and Their Use
B545 Specification for Electrodeposited Coatings of Tin
B605 Specification for Electrodeposited Coatings of Tin-Nickel Alloy
B650 Specification for Electrodeposited Engineering Chromium Coatings on Ferrous Substrates
B689 Specification for Electroplated Engineering Nickel Coatings
B733 Specification for Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Metal
B734 Specification for Electrodeposited Copper for Engineering Uses
B735 Test Method for Porosity in Gold Coatings on Metal Substrates by Nitric Acid Vapor
B741 Test Method for Porosity In Gold Coatings On Metal Substrates By Paper Electrography
B798 Test Method for Porosity in Gold or Palladium Coatings on Metal Substrates by Gel-Bulk Electrography
B799 Test Method for Porosity in Gold and Palladium Coatings by Sulfurous Acid/Sulfur-Dioxide Vapor
B809 Test Method for Porosity in Metallic Coatings by Humid Sulfur Vapor (Flowers-of-Sulfur)
B866 Test Method for Gross Defects and Mechanical Damage in Metallic Coatings by Polysulfide Immersion
B877 Test Method for Gross Defects and Mechanical Damage in Metallic Coatings by the Phosphomolybdic Acid (PMA) Method
ICS Number Code 25.220.40 (Metallic coatings)