Effect of graphite concentration on the friction and wear of Ni–Al2O3/graphite composite coatings by a combination of electrophoresis and electrodeposition

• Ni–Al2O3/graphite coatings were prepared by electrophoresis and electrodeposition.
• Effect of graphite concentration on the friction and wear behavior were investigated.
• The Al2O3 particles deposition process and wear mechanism of coatings were discussed.
• The optimal graphite particles concentration in EPD bath for the coatings is 1.5 g/L.
• The prepared coating shows improved wear resistance and self-lubricating properties.

The purpose of this work was to investigate the sliding friction and wear of a novel Ni-based coating. Ni–Al2O3/graphite composite coatings were prepared on LY12 aluminum alloys using a three-step process that involved electrophoresis and electrodeposition. Uniform composite coatings with a high volume content of particles were prepared. The effects of the deposition process on the wear mechanism of these coatings were investigated. The microindentation hardness decreased, while the friction coefficient and wear loss of the coatings initially decreased and then slowly increased as the graphite content was increased. The optimum value of the graphite particle concentration in the electrophoresis bath was 1.5  g/L. The embedded graphite particles formed a transfer film on the contact area and reduced the sliding friction coefficient of the composite coatings. The new Ni–Al2O3/graphite composite coating presented excellent lubricating properties and wear resistance largely due to the effects of graphite and Al2O3 particles.