Microstructure and Tribological Properties of Ni-Base Coatings under Different Lubrication Conditions

Abstract

In order to improve the tribological properties of aluminum alloy cylinder wall, Ni-base coatings were fabricated by atmospheric plasma spraying on aluminum substrate. The composition, microstructure characterization and tribological properties of Ni-base coatings were investigated under different lubrication conditions. The results showed that as-sprayed Ni-based coatings were mainly consisted of γ-Ni solid solution, Ni3B, Cr7C3, Cr6C and Cr3B2 phase. The microstructure of coatings exhibited excellent deposit integrity and density, whilst a typical lamellar structure was observed because the molten droplets successively impinged and spread on the substrate or previously deposited layers to form continuous splats. Friction and wear testing results showed that Ni-based coating performs better than grey cast iron HT200 for the actual application of cylinder block and cylinder liner, especially under boundary lubrication. It was proposed that the excellent mechanical properties ensure the as-sprayed coating with low friction coefficient and wear rate under different lubrication conditions, In addition, the existence of pores was benefitted for the improvement of tribological properties under boundary lubrication.