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 im- 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 pre-sputtering times with argon ions to vary the adhesion on the steel substrate. The adhesion behaviour of the films were 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 the adhesion.