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Characterization of Coatings and Machined Surfaces by Surface Acoustic Waves

: Schneider, D.; Schultrich, B.; Siemroth, P.; Leonhardt, M.; Franke, A.

2nd International Conference The Coatings in Manufacturing Engineering 2001. Conference Proceedings
Hannover, 2001
International Conference The Coatings in Manufacturing Engineering <2, 2001, Hannover>
Fraunhofer IWS ()
Geometrie; Schichtdicke; Rauhigkeit; Ultraschall; Keramik; Kohlenstoff-Schicht; Multischicht; Nanomaterialien; Grenzfläche; Laser-Akustik; Nanotechnologie

The laser-acoustic technique based on surface acoustic waves has proved to be an interesting test method for coatings and material surfaces. The central point of the laser-acoustic technique is measuring the phase velocity of the surface acoustic wave depending on frequency and fitting a theory to deduce elastic modulus or thickness of the film. For a completely homogenous material, the phase velocity is constant, but for coated materials the curve may ascend or descend, depending on film and substrate properties. The capability of the laser-acoustic method is demonstrated for three very different examples. The elastic modulus E of ultra-thin diamond-like carbon films with thickness down to 4 nm was determined. Depositing the film on cold substrates leads to a modulus of about 500 GPa. Increasing the substrate temperature reduces the modulus distinctly, revealing the reducing sp3-fraction. Testing metal layers of titanium proved their modulus to be very sensitive to the tech nological parameters of deposition. The reduction by more the 30 % compared to the bulk value was explained by the porosity of the films. Machining layers in silicon semiconductor material were investigated. The damage state of the surface is shown to be sensitively detectable by the laser-acoustic method.