Friction and wear of nanocrystalline Co and Co–W alloy coatings produced by pulse reverse electrodeposition

Abstract

Nanocrystalline cobalt (Co) and cobalt–tungsten (Co–W) alloy coatings were produced by pulse reverse electrodepositon from an aqueous bath. The electrochemical corrosion and tribological properties of the coatings under different conditions were characterized. The results show that the corrosion resistance of the nanocrystalline Co is better than that of the nanocrystalline Co–W alloy coating due to its lower surface roughness and smaller grain size. The nanocrystalline Co–W alloy displays better wear resistance and friction reduction compared to the nanocrystalline Co coating. The friction coefficients and wear rates of the nanocrystalline Co–W alloy coating are affected by the counterpart materials and the test conditions including the applied load and sliding speed. The friction coefficient is raised by the ceramic surface although the increase is still relatively small to a steady-state values less than 0.32. The wear rates of the Co–W alloy coating at high load are slightly higher than those at low load. The increase of initial contact pressure between the coating and the counterpart balls and the hardness of the counterpart balls results in the decreased wear resistance for the Co–W alloy coating independent of applied loads. The wear mechanisms of the nanocrystalline Co and Co–W alloy coatings involved in different sliding conditions and counterpart materials are explained and related to their friction and wear properties.