Non-destructive evaluation of the mechanical behaviour of TiN-coated steels by laser-induced ultrasonic surface waves

Measuring the propagation velocity of ultrasonic surface waves has been used to determine the Young's modulus of TiN films on steel. Wide-band surface-wave pulses are generated by a pulsed nitrogen laser and detected by a piezoelectric PVDF-foil transducer. A spectrum of the surface-wave phase velocity is obtained from the Fourier transformation of the surface-wave signals. The TiN films were deposited after different presputtering times with argon ions to vary the adhesion on the steel substrate. The adhesion behaviour of the films was investigated with the scratch tester. A correlation was found between the Young's modulus of the film material and the acoustic emission activity in the scratch test, which has been shown to be a suitable measure for adhesion.