An experimental method was developed for determination of residual stresses in
electrochemically metallized (brush-plated) coatings by measuring the slit increment of the unclosed
ring strip substrate after deposition process. The substrate is fixed to a mandrel, which makes free
slipping of the edges as well as momentless deformation of the coated substrate possible. The
calculation formula is extended Stoney’s formula which takes into consideration the real shape of
the substrate, and the difference of the elasticity moduli of the coating and the substrate materials.
The difference between the coefficients of thermal expansion of the coating and substrate materials
is also taken into account. Residual stresses are determined for four materials (nickel, zinc, copper,
silver) from six electrolytes.
Residual stresses in most coatings have a significant influence on adhesion, on mechanical properties and on tribological performance. Residual stress can not be measured directly, rather strain is measured and stress is calculated. In this study residual stresses were investigated in thick thermal Ni95Al5 and cold sprayed Ni, Cu, NiZn, AlZn powder coatings using the semi-destructive hole-drilling and layer growing curvature methods. Residual stresses obtained for the thermal spray coating were compressive and with a relatively large deviation of the results indicating the nonuniformity of residual stress. Cold sprayed coatings have more uniform structure than thermal sprayed coatings. Residual stresses were compressive, and results obtained by hole-drilling and curvature method were comparable.
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