ASTM B659-90(R2021) pdf free download

ASTM B659-90(R2021) pdf free download.Standard Guide for Measuring Thickness of Metallic and Inorganic Coatings
4. Reliability of Methods
4.1 All methods covered by this guide are sufficiently reliable to be used for acceptance testing ofmany electroplated and other coatings. That is, each method is capable of yielding measurements with an uncertainty of less than 10 % of the coating thickness over a significant range of coating thick- nesses when used by properly instructed personnel.
5. Nondestructive Methods
5.1 Magnetic Methods—These methods employ instruments that measure the magnetic attraction between a magnet and the coating or the substrate or both, or that measure the reluctance of a magnetic flux path passing through the coating and the substrate. These methods, in practice, are limited to nonmag- netic coatings on carbon steel (Test Method B499 and ISO 2178) and to electrodeposited nickel coatings on carbon steel or on nonmagnetic substrates (Test Method B530 and ISO 2361) and to nonmagnetic autocatalytically deposited nickel- phosphorus alloys on carbon steel (Test Method B499 and ISO 2176). Coating thickness gages of this type are available commercially. 5.2 Eddy-Current Method—This method employs an instru- ment that generates a high-frequency current in a probe, inducing eddy currents near the surface of the test specimen. The magnitude ofthe eddy currents is a function ofthe relative conductivities of the coating and substrate materials and the coating thickness. Because variation in the electroplating process can change the electrical properties of the coating and, hence, instrument response for a given thickness, the use of eddy-current instruments is usually limited to the measurement of nonconductive coatings on nonmagnetic basis metals (Test Method B244 and ISO 2360). These instruments are, however, also suitable for the thickness measurement of high- conductivity metal (for example, copper and silver) coatings on nonconductive substrates. Coating thickness gages of this type are available commercially.5.3 X-Ray Fluorescence Methods: 5.3.1 These methods cover the use of emission and absorp- tion X-ray spectrometry for determining the thickness of metallic coatings up to about 15 µm. The upper limit may be significantly above or below 15 µm depending on the coating material and on the equipment used. When exposed to X rays, the intensity of the secondary radiation emitted by the coating or by the substrate followed by attenuation by the coating is measured. The intensity ofthe secondary radiation is a function of the coating thickness. 5.3.2 In multiple coatings the X-ray method is generally applicable to the final metal coating. 5.3.3 Suitable equipment is available commercially (Test Method B568 and ISO 3497). 5.4 Beta Backscatter Method: 5.4.1 The beta backscatter method employs radioisotopes that emit beta radiation and a detector that measures the intensity of the beta radiation backscattered by the test speci- men. Part of the beta radiation entering the material collides with atoms of the material and is scattered back towards the source. The intensity of the backscattered radiation is a function, among others, of the coating thickness. A measure- ment is possible ifthe atomic number ofthe coating material is sufficiently different from that of its substrate and if the beta radiation is ofsuitable energy and intensity. The method can be used for measuring both thin and thick coatings, the maximum thickness being a function ofthe atomic number ofthe coating. In practice, high atomic number coatings, such as gold, can be measured up to 50 µm, while low atomic number coatings, such as copper or nickel, can be measured up to about 200 µm. 5.4.2 Coating thickness gages of this type are available commercially (Test Method B567 and ISO 3543).
6. Semidestructive Methods
6.1 Coulometric Method: 6.1.1 Coating thickness may be determined by measuring the quantity of electricity consumed in dissolving the coating from an accurately defined area when the article is made anodic in a suitable electrolyte under suitable conditions. The change in potential occurring when the substrate is exposed indicates the end point of the dissolution. The method is applicable to many coating-substrate combinations (Test Method B504 and ISO 2177). 6.1.2 Coating thickness instruments employing this method are available commercially. 6.2 Double-Beam Interference Microscope Method—A step is formed between the coating surface and the substrate surface by dissolving a small area of coating. The height of this step is measured with a double-beam interference microscope. The method is applicable to thin coatings such as usually used for decorative chromium. It can be used to measure transparent oxide coatings without the need offorming a step (Test Method B588).