High Strength Ni-Fe-W and Ni-Fe-W-P Alloys Produced by Electrodeposition

Abstract

Ni-Fe-W alloys were produced by electrodeposition from an ammoniacal citrate bath having nickel sulphate, ferric sulphate and sodium tungstate as sources of nickel, iron and tungsten, respectively. The alloys prepared at low current densities have nanocrystalline structure, while those prepared at high current densities are amorphous. X-ray diffraction results show that the structure changes gradually from nanocrystalline to amorphous phase with an increase of current density. As the current density increases, tungsten content increases while iron content decreases. The hardness of the alloys increases with increasing tungsten content. The best mechanical properties among all the alloys are obtained for 51Ni-29Fe-20W alloy prepared at 600 A/m². Effect of sodium hypophosphite on the composition of the alloys produced at 2000 A/m² was also studied. Addition of hypophosphite causes a decrease in tungsten content of the alloys. Further increase in the hypophosphite content causes a decrease of both iron and tungsten contents and an increase of phosphorus and nickel contents. For the alloys deposited from solutions containing sodium hypophosphite more than 0.03 mol/L, the total molar content of tungsten and phosphorus remains constant at 20 at%.