Application of resonant ultrasound spectroscopy to determine elastic constants of plasma-sprayed coatings with high internal friction

We present a novel modification of resonant ultrasound spectroscopy (RUS) for analysis of elastic constants of plasma-sprayed coatings in the 'as sprayed' state, i.e. without removing the substrate. This modification is suitable for coatings with high internal friction (Q− 1 ≳ 10− 2), which cannot be measured by RUS in the free-standing state due to strong damping. In combination with through-transmission measurements, this modification is able to provide full anisotropic tensor of elastic constants of the coating. As an illustrative example, the proposed methodology is applied to two steel coatings prepared by water-stabilized plasma (WSP) spraying. In addition to the moduli, also the internal friction parameters of the coatings are obtained. The results of RUS are compared to moduli determined by four-point bending tests, and it is shown that the anisotropic elasticity of both examined materials exhibits an elliptic form of transversal isotropy with four independent elastic coefficients.