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Nondestructive evaluation of TiN films with interface defects by surface acoustic waves

: Ollendorf, H.; Schneider, D.; Schwarz, T.; Mucha, A.


Surface and coatings technology 74/75 (1995), S.246-252
ISSN: 0257-8972
Fraunhofer IWS ()
acoustic emission; acoustic surface wave; adhesion test; Adhesionstest; akustische Emission; akustische Oberflächenwelle; critical load; Dünnschichtcharakterisierung; Eigenspannung; Kratztest; kritische Last; laser induced ultrasound; laser-induzierter Ultraschall; nondestructive testing; residual stresses; scratch test; thin film characterisation; zerstörungsfreie Prüfung

Surface acoustic wave (SAW) measurements are a fast and reliable way to get information about the elastical properties of thin film coatings, Measuring the surface wave phase velocity which is dependent on frequency and performing the inverse solution of dispersion relation for surface wave propagation in coated materials enable to determine the elastic parameters of the film and substrate material. A measuring equipment is used where wide-band surface wave impulses are generated by short laser pulses and received with a piezoelectric transducer. The surface wave phase velocity is obtained by Fourier transforming the impulse form. In this work we are interested in Young's modulus of the film material and its relation to the defects in the interface region to the substrate. Young's modulus is a characteristic material parameter, depending on atomic composition and on the microscopic structure of the material. It is theoretically and experimentally established that, if defects like flaws are incorporated, Young's modulus is reduced in comparison to bulk material. The examined samples were steel pieces (42CrMo4) coated with TiN by ion plating. During the deposition process we have only varied the duration of the ion etching process, while keeping all other technological parameters constant. The ion etching is responsible for the adhesion of the coating by removing residual contamination from the substrate surface. In this way a more or less non-defective interface zone is built up. The procedure of varying only the etching time allows to get different interface properties while leaving film properties constant. Film properties were characterised by means of Auger-, x-ray texture-, and dynamic hardness measurements. It could be proved that there is a significant correlation between Young's modulus and the etching time. A reduction of the etching time causes a reduction of Young's modulus. Conventional adhesion tests (scratch test) were performed for comparison.