Laser-induced surface acoustic waves for evaluation of elastic stiffness of plasma sprayed materials

The elastic properties of plasma sprayed deposits have been evaluated using a laser-excited surface acoustic wave (SAW) technique and an inversion processing analysis. The SAWs including Lamb and Rayleigh waves were generated in plasma sprayed NiCoCrAlY and ZrO₂, respectively, and their group velocity dispersions were used to determine the elastic properties (i.e.Young's modulus, Poison's ratio and density) of the deposits. Estimated elastic moduli from the velocity dispersions of A₀-mode Lamb waves are in the range of 40–140 GPa for the deposits, which are much lower than the values 220–240 GPa of the comparable dense materials. The dramatic reductions in modulus and density of ZrO₂ deposit have been attributed to the presence of high porosity and particularly microcracks. Moreover, this study has emphasized on exploiting the applicability of each kind of the SAWs for the elastic property evaluation of different sprayed materials. Both Lamb and Rayleigh wave dispersions are useful for the estimation of APS and VPS-deposited NiCrAlY, but S₀-Lamb and Rayleigh waves are exceptional for that of sprayed ZrO₂, because of its characterization of high acoustic attenuation and inconsequent displacement across the weak bonded interface of ZrO₂ and substrate.