Cross-sectional Observation of Ni/Cu and Ni/Ni-P Multilayer Films Electrodeposited with Pulses of a Constant Current and their Dependence of Wear Resistance on Layer Thickness

Abstract

To improve the wear resistance of deposited films, Ni multilayer films containing copper （Cu） or phosphorus （P） were prepared electrochemically by application of pulses of a constant current from a NiSO₄ aqueous solution in the presence of copper sulfate （CuSO₄） or phosphoric acid （H₃PO₃）. Films prepared on the copper （Cu） substrates have structures （Ni/Cu or Ni/Ni-P） that include a Ni layer of controlled thickness and a thin Cu or Ni-P layer, where the two layers （Ni and thin Cu layers or Ni and thin Ni-P layers） are laminated alternately. The wear resistance of the prepared Ni/Cu and Ni/Ni-P multilayer films was higher than those of conventional Ni-P bulk films or an Ni/Cu multilayer film composed of Ni and Cu layers having equal thickness. It is noteworthy that the Ni/Ni-P multilayer film wear resistance improved with decreasing thickness of the Ni layer, even for Ni layer distance less than 10 nm. The Ni/Ni-P multilayer exhibited the best wear resistance performance at the minimum Ni layer distance used in this study: 3 nm. A new wear resistive multilayer was developed.