Evaluation of Adhesion Strength of Plasma-Sprayed Coating for Complex Loading by Tensile Test

A method is developed for evaluating the adhesion strength of coating on substrate using flat tensile sample. The developed method takes into account the complex stress states that occurs in the vicinity of the free edge of the coating during its delamination. Considering the problem of coating on a subtrate by theory of elasticity, it is shown that the delamination of the coating is caused by the combined effect of the interface shear stresses and the normal peeling stresses. An approach accounting for the combined effect is proposed and it is evaluated for determining the adhesion strength of plasma-sprayed Co-Cr alloy coatings of various thicknesses. Numerical calculations of the tensile samples with the coatings using the finite element method showed that the stresses in the vicinity of the free edges of the coating initiate failure. The combined stress approach to adhesion strength was found to be more accurate and reliable than the common shear-lag approach.