Stress-strain curves of selected plasma-sprayed ceramic coatings were measured by the four-point bending method, with the coating deposited on the compressive or tensile side of the substrate. Uniaxial stress s and deformation e in the central plane of the coating were determined. For deformations |e| < 0.1% Young's moduli can be considered constant and were found to be from 18 to 52 GPa. For deformations 0.1% < |e| < 0.4% the measured curves show that Young's modulus increases with the compressive deformation and decreases with the tensile deformation. The contribution of intrasplat microcracks to the nonlinearity is discussed. In tensile loading, microcracks are opening and Young's modulus is decreasing whereas in compression closing of microcracks leads to increase in Young's modulus. Two-parametric equation containing linear and quadratic term was successfully used to describe the nonlinear stress-strain curves of plasma sprayed ceramic coatings.
