Thermal sprayed coatings are used in various applications often dedicated to corrosion and wear protection.Poresand other coating imperfections reduce corrosion and wear resistance and/or necessitate higher coating thicknesses. To improve the quality of thermal sprayed coatings, various post-treatment processes can be used. Characterisation of the efficiency of sealing was studied by metallographic examination andcomparative investigation of the corrosion and wear behaviour of the thermal sprayed coatings used with and without sealing and also by measuring the insulation resistance of the coating system. The results differ among the sealants. It is possible to remove the sealants from the coatings by mechanical treatment. Corrosion tests of the sealants demonstrate their efficiency in closing the interconnected pores and, consequently, preventing corrosion.
The characterisation of the effectiveness of sealing was studied by metallographical investigations as well as comparing the investigations with respect to the corrosion- and wear behaviour of the used thermal sprayed coatings and last but not least by measuring of the insulation resistance of the coating system. The obtained results show that there are differences between the used sealants and it is possible through a mechanical treatment of sealed coatings to remove the sealants from the coatings. In the corrosion test the sealants show their efficiency. The sealants insulate the open porosity and prevent the corrosion attack owing to the interconnected pores.
Lock-in thermography is a nondestructive inspection method based on modulated heat transport in combination with infrared imaging. Measurement times are relatively short, about 3 or 4 minutes, and the method is amenable to inspecting a wide range of large and small parts. This paper describes the basic principle behind the method and its application to different thermal sprayed coatings (e.g., Cr-steel, Al2O3). It explains how the test samples were prepared with artificial defects simulating delaminations, inclusions, and other types of imperfections and how the method performed in each case.
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