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Hochfrequenter Ultraschall und Mikrothermographie - zwei Verfahren zur hochauflösenden zerstörungsfreien Beschichtungsprüfung
High-frequency ultrasound and microthermography - two techniques for high-resolution, non-destructive coating tests
The two techniques high-frequency ultrasound in the frequency range 10-100 MHz and microthermography (photothermal radiometry) at modulation frequencies of 2 Hz to 5 kHz are discussed in comparison with respect to testing of coatings. Tungsten carbide coatings on steel are studied with high-frequency ultrasound , copper layers on aluminium nitirde are studied with microthermography. In one case thermal properties, in the other case elastic properties are of importance. Advantages of microthermography are due to the non-contact operation, advantages of high-frequency ultrasound are due to the direct relation between time-of flight and defect depth