Effect of Current Density on Performance of Nano-TiN/Ni Composite Coating Electrodeposited from Sulfamate Bath

With the sulfamate bath containing TiN nanoparticles as the basic bath, the nano-TiN/Ni composite coatings were deposited on 45 steel surface by ultrasonic-pulse electrodeposition method. The effects of current densities on the morphology and microhardness of the composite coatings and on the TiN content and distribution at the surface were analyzed. The results show that when the current density changed between 2 A·dm-2 and 5 A·dm-2, the microstructures of the composite coatings were compact and the thicknesses were uniform, and the thickness increased with the increasing current density. With the increase of the current density, the surface grains in the composite coatings first refined then enlarged, and the microhardness first improved then decreased. When the current density was 4 A·dm-2, the surface of the composite coating was plain and the surface and cross-section microhardness reached the largest value of 677 HV and 763 HV respectively. The TiN content in the surface of the composite coating first increased then decreased with the increase of the current density, and achieved the highest value and a relatively uniform distribution at the current density of 4 A·dm-2.