Comparative Analysis of Methods for Assessing Adhesion Strength of Thermal Spray Coatings

The paper presents the comparative analysis of existing methods for accessing the adhesive strength of thermally sprayed coatings on witness samples and products in research and industrial laboratories. The adhesive method of normal separation for cylindrical witness samples with a diameter of 25 mm, a height of 16...45 mm and a coating thickness of at least 0.2 mm is pointed out among the quantitative approaches described in both international and domestic standards. An alternative pin test having no restrictions on the ultimate strength of adhesion was used to evaluate conical witness samples with an end section diameter of 1.5...2.0 mm and a coating thickness of 0.3...0.5 mm. The shear method presents two possible adhesion measurement tests: with cylindrical witness samples having the diameter of 25 mm, the width of the annular coating section of 4 ... 30 mm and the thickness of the working layer not exceeding 0.1 mm and prismatic ones with linear dimensions of shear section of 2.5...5.0 mm and the coating thickness of at least 0.25 mm. During the tests all methods were characterized by irregular loading of the flat section of the coating. Mathematical models for calculating the actual value of the tensile and shear adhesion strength are presented, taking into account the appearance of additional bending and shear forces when loading the coating.

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