Nickel electrodeposition from all-sulphate and all-chloride baths. Texture and microhardness

In the nickel electrocrystallization process there appears a strong specific inhibition of crystal growth. Various chemical species, such as Ni(OH)2 gaseous H2 or Hads which exist or are formed in the metal-electrolyte interface according to the electrolysis conditions, are selectively adsorbed in the continually regenerated metallic surface and determine the texture of the electrodeposits. The aim of this work is to study the correlation between the texture and the microhardness of nickel deposits. The preferred orientation of the deposits, prepared from all sulphate and all chloride baths, was studied by X-ray diffractometry and the corresponding texture diagrams were traced as a function of the solution pH and the cathodic current density. The microhardness of the deposits was determined by the Vickers method. It is shown that the textures and the microhardness of the deposits depend on the electrolysis conditions, but the hardness seems to be independent of the crystallite orientation, in spite of the related bibliographic references. The preferred orientations and the microhardness of the nickel deposits are produced by the same cause: the specific inhibition of the cathodic surface during the electrodeposition determines the orientation of the crystallites, produces deformation of the crystal lattice and increases the hardness of the deposits.