Determination of the penetration behavior of sealers in thermally sprayed coatings (APS, HVOF, LDS, etc.)

Does the sealer work for your thermally sprayed coating? Have you ever asked yourself this question or are you still working according to the motto “nobody has ever complained”?

We are not satisfied with just selling sealers, we also want these sealers to work. For this reason, we provide our customers with proof of function on request regarding the penetration behavior of our sealers in their thermally sprayed coatings.

 

The sealer and thermal spray coating form a unit and should ideally be matched to each other. In practice, however, too little attention is often paid to sealing as a “post-treatment method” (see DIN EN ISO 14924). However, sealing is a comparatively simple process step which can have an enormous impact on the service life of the overall coating system. The smallest pores or cracks in the thermal layers can lead to premature failure, even with extremely dense layers such as HVOF (pore content < 1%). A good sealer is able to prevent such damage. The task of the sealer seems simple: penetrate the pores and seal them permanently.

Unfortunately, the process is not so trivial in practice and the large number of influencing parameters requires a much deeper understanding of the interaction between the sealer and the thermal spray coating. A decisive criterion for successful sealing is the penetration and sealing behavior of the sealer. In order to guarantee lasting protection in the event of coating erosion (processing, wear), the sealer must penetrate as deeply as possible into the coating. At the same time, however, it must also seal, which is often not a prerequisite. Classic detection methods such as microscopy reach their limits here. If the penetration depth of the sealer can still be easily detected, optical analysis does not provide any information as to whether the sealer also seals.

However, it is precisely this verification that is important if the function of the sealant-layer system is to be tested. In order to determine the functional penetration depth (depth to which the sealant layer system is gas-tight), we carry out a specially developed test. Using the DIPERM measurement, we determine the functional penetration depth of the sealer in customer-specific layers and thus prove that the sealer works for the respective layer and provides real protection. We also use the DIPERM method to develop sealers and achieve optimizations for our customers. For one customer, for example, we were able to develop a sealer for Al2O3 APS coatings that achieves a functional penetration depth of 80% and is applied to a hot component surface of +80°C. Compared to the previously used sealer, which had to be applied at room temperature, the production process could thus be shortened by approx. 12%. The result is an increase in efficiency combined with a proven protective effect. A double benefit for our customer, so to speak. We would also be happy to support you in optimizing your “sealer” post-treatment.

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Mr. Carsten Kunde

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Mr. Erkan Polat

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