Tensile deformation behavior of plasma-sprayed Ni-45Cr coatings

Deformation behavior of plasma-sprayed Ni-45Cr coatings was studied in terms of stress-strain relation and modulus changes under tensile loading. The tensile loading was applied in both directions parallel and perpendicular to the lamellar plane of the coatings. The influences of spray distance on Young's modulus and Poisson's ratio of the coatings were investigated. The Young's modulus was measured from both directions parallel and perpendicular to the lamellar plane. Results showed a linear relation between the stress and strain in the direction parallel to the lamellar plane. The similar linear stress-strain relation in the direction perpendicular to the lamellar plane was revealed only when the tensile loading with up to a certain value was applied, while a nonlinear stress-strain relation prevailed under a higher tensile load. The increase of the proportional limit of the coating was observed under repetitive tensile loading perpendicular to the lamellar plane. The modulus measured from the direction parallel to the lamellar plane changed from 78 GPa to 92 GPa. Spray distance showed minor effect on the Young's modulus. Moreover, the modulus measured from the direction perpendicular to the lamellar plane, changing from 48 GPa to 64 GPa, was lower than that obtained from the direction parallel to the lamellar plane. It is clear that plasma-sprayed metallic coating presented an anisotropic elastic behavior. In addition, it was found that the coatings yielded a Poisson's ratio of 0.13-0.15 which is lower than that of bulk materials. Spray distance also has no significant influence on the Poisson's ratio of coatings.