The thickness of coating is one of the important marks to measure the quality of coating. The thickness of the coating affects the reliability and use value of the product to a great extent. Through the detection of coating thickness, in addition to evaluating whether the workpiece with tolerance index or repair size requirements is reasonable, it can also directly or indirectly evaluate the corrosion resistance, wear resistance, porosity and other properties of thermal spraying coating. Therefore, it is widely used in coating quality inspection and process research.

The inspection of coating thickness is generally divided into two types: average thickness and local thickness. Because the local thickness can reflect the quality of the product better than the average thickness in practical application, in most cases, the local thickness or the local average thickness of the coating is measured. During thickness measurement, at least three thicknesses shall be measured at representative or specified positions, and the average value shall be calculated as the result of thickness measurement.

There are two kinds of testing methods for coating thickness: destructive testing and nondestructive testing. Destructive testing methods include: drop method, liquid flow method, chemical dissolution method, coulometric method, metallographic microscope method, profile method and interference microscope method. Nondestructive testing methods include magnetic method, eddy current method, X-ray fluorescence thickness measurement method, ray back scattering method, light cutting microscope method and energy spectrum method.

Here are several common methods for measuring the thickness of thermal spraying coating

Metallographic microscopy is one of the physical methods to measure the coating thickness. The normal metallographic method is used to make the section sample of the coating to be tested, and then the magnified image of the vertical section of the coating to be tested is observed on the metallographic microscope with a micrometer eyepiece, so as to directly measure the local thickness of the coating. This method has the advantages of high measurement accuracy, sufficient basis, intuitive judgment and so on, because it directly measures the section thickness of the coating under a certain magnification. However, the operation of this method is relatively complex when the sample is made, and it is generally used for strict thickness control, or other thickness measurement methods to verify and arbitrate the test pieces with disputed results or for laboratory measurement.

Metallographic thickness measurement is a method to observe and measure the thickness of the longitudinal section of the coating by using a special metallographic microscope with a certain magnification and a micro eyepiece. In order to make the cross section of the coating meet the requirements of metallographic microscope, the coating to be tested shall be cut, edge protected, inlaid, polished and chemically etched before thickness measurement, and then the coating to be tested shall be made into the qualified sample.

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