Surface engineering with functionally graded coatings: a numerical study based on the boundary element method

Numerical results are presented on subsurface stress distributions in bi-layer and graded multilayer coatings on monolithic substrates under plane strain contact conditions (cylinder on flat contact geometry). The case of a coating stiffer than the underlying substrate is considered, with a coating/substrate modulus ratio of 2.44, and a medium ‘generalized thickness’ t*=t(f)/a=0.5.44t(f)/is the absolute coating thickness and a the Hertzian contact half width in cylinder/flat (2D) contact coatings (a stack of 10 individual layers) are considered with moduli progressively increasing from the coating/substrate interface towards the extreme coating surface; this way interface stress discontinuities can be eliminated and stress intensities reduced both in the substrate and in the coating.