Tailoring the physical properties of electrodeposited CoNiReP alloys with large Re content by direct, pulse, and reverse pulse current techniques

The composition, surface morphology and structure of CoNiReP alloy films with large Re content (up to 27 at%), obtained in a citrate-glycine based electrolyte have been studied as a function of the electrodeposition technique. Direct current (DC), pulse plating (PP) and reverse pulse plating (RPP) were considered with cathodic current densities from -50 mA cm^-2 to -250 mA cm^-2. The mechanical and magnetic properties have been analyzed and the data obtained has been correlated with composition and crystallographic structure. For values of j (DC), j_on (PP) and j_c (RPP) below -100 mA cm^-2, Co-rich, P-containing deposits are obtained. Beyond these current densities, both the quantities of Ni and Re increase simultaneously at the expense of Co and P, the latter virtually falling to zero. The highest Re percentage (25-27 at%) was achieved in both PP and RPP conditions at a cathodic pulse of -250 mA cm^-2. All the films were either entirely nanocrystalline in nature or partially amorphous. Hardness values as high as 9.2 GPa have been found in PP plated Co₆₄Ni ₁₈Re₁₈ deposits. Besides the large hardness, the incorporation of Re in the films leads to high elastic recovery values. The magnetic character of the deposits ranges from soft to semi-hard ferromagnetic.