A model for compressive coating stresses in the scratch adhesion test

Despite the widespread use of the scratch adhesion test, there is no model available to determine the critical coating stress for initiating interfaci al failure, so that ranking the coating-substrate adhesion of coated system s with different mechanical properties is impossible. In this study, a math ematical model is developed to calculate the distribution of compressive st resses in a thin coating induced by a scratch indenter. For ease of use in practice, a simple: equation, sigma (Sm) = 0.15 (P-c H-f / H)(0.5) E-f(0.3) E-0.2 / R, is then derived from the model, where a,, is the critical mean compressive stress in the coating for interfacial failure, P, is the critic al normal load measured from the scratch adhesion test, H, and E, are the h ardness and Young's modulus of the coating, H and E are the hardness and Yo ung's modulus of the substrate, and R is the indenter radius. This equation is useful for ranking the coating-substrate adhesion of different coated s ystems, or, for estimating the critical mean coating stress for interfacial failure. (C) 2001 Elsevier Science B.V. All rights reserved.