Electrodeposition of nanocrystalline nickel assisted by flexible friction from an additive-free Watts bath

Nanocrystalline nickel coatings with different grain sizes were prepared by a modified electrodeposition technology assisted by flexible friction from an additive-free Watts bath. The effects of various flexible media, e.g. polymers, bio-bristles and natural fibers, on the morphology, preferred orientation, and grain size of electrodeposited nickel coatings were studied at different temperatures. The results demonstrate that flexible friction can effectively hinder the aggregation growth of adsorbed atoms and remove some surface-adsorbed species, to significantly refine the grain size and change the preferred orientation of deposits. The crystal growth inhibition effect significantly increases with temperature and incremental contact pressure of flexible friction. At 50 °C, the nanocrystalline nickel coating gained by bio-bristle friction is the smoothest and has a dense surface morphology with a (111) preferred orientation. The corresponding grain sizes concentrate in the range of 20-30 nm, and the microhardness is between 470 and 500 HV, which is higher than that of the traditional electrodeposited nickel coating (320 HV). The grain refining mechanism, texture evolution and microhardness variation of nickel deposits assisted by flexible friction are discussed.