The dynamical resonant technique in free bending mode used for the determination of constants of elasticity has been developed in view to characterize coated materials. It has first been applied to homogeneous single coatings from room temperature up to 1,100°C for thicknesses varying from 2 to 200 μm with the help of a formalism of composite beam. This formalism has then been extended analytically to three and four layers in order to characterize multicoated materials. For thermochemical treatments presenting a gradient of mechanical properties, a simplified n-layer model allows to estimate the modulus gradient as a function of depth.