Influence of molybdenum on the mechanical properties, electrochemical corrosion and wear behavior of electrodeposited Ni-Mo alloy

In the present work, the influence of molybdenum (Mo) content on the grain size, hardness, corrosion and wear behavior of Ni-Mo alloy coatings electrodeposited from citrate electrolyte has been studied. Crack free Ni-Mo alloy with different Mo content (3, 5, 6, 9 and 12 at.%) was obtained using direct current and pulsed current electrodeposition. It was observed that the grain size of Ni-Mo alloy decreased with increase in Mo content. Hardness of the coatings increased with Mo content and decreased subsequently above 9 at.% Mo as per inverse Hall-Petch effect. Potentiodynamic polarization tests carried out in 2 N H2SO4 suggested increase in both corrosion current and passive current density with increase in Mo content. In addition, both friction coefficient and dry sliding wear rate of Ni-Mo coatings decreased with increase in Mo content. The results are rationalized based on grain size and Mo content in the coatings. Finally, Ni-Mo and Ni-W coatings were compared with hard chrome with respect to mechanical properties, wear and corrosion resistance. Results indicated that, Ni-Mo coatings exhibit least friction coefficient (0.2–0.3) amongst Ni-W and hard chrome coatings.