A novel electrodeposited Ni–P gradient deposit for replacement of conventional hard chromium

In this paper Ni–P gradient deposits with a graded change of P content in the direction of thickness were prepared from a single plating bath using an electrodeposition method. The tribological properties of the heat-treated Ni–P gradient deposits at room temperature compared with ungraded Ni–P after heat treatment at 400 °C was investigated using a ball-on-disc tribometer. Also, tribological properties of heat-treated Ni–P gradient deposits against a silicon nitride ball were examined in the temperature range from room temperature to 600 °C with a comparison to conventional hard Cr deposits. Results show that the wear resistance of graded Ni–P alloys was approximately two times that of ungraded deposits. In addition, graded Ni–P deposits exhibited better wear resistance and lower friction coefficient than that of hard Cr deposits both at room and high temperature wear conditions. The main reason may be that the formation and propagation of through-thickness cracks within heat-treated Ni–P deposits during the wear process were effectively inhibited due to the introduction of graded composition and structures.