Effect of spherical microceramics on hardness and wear resistance of Ni-based thermal sprayed coatings

Abstract

In the present study, the spherical alumina microceramics was used to improve tribological properties and wear resistance of nickel-based thermal sprayed coatings. The powder mixtures containing 5, 10 and 20 wt. % of Al2O3 spherical alumina having particles size of 0-40 μm were prepared. The coatings of ~0.9–1.1 mm thickness were formed by two-step spray and fuse process. As a reference, the nickel-based coatings without ceramics addition and nickel-based coatings containing 10 wt. % of Al2O3 with angular particles shape was used. The microstructural analysis by scanning electron microscopy showed that after spraying only a part of spherical particles retains their initial spherical shape. The majority of ceramic microspheres melt and form semi-spherical shells surrounding nickel particles and splats. With the addition of 10 wt. % Al2O3, the hardness was increased by ~55 %, the mass loss was reduced two times and the friction coefficient diminished by ~35 %. With the increase of ceramics amount up to 20 wt. % Al2O3, the worsening of properties was observed, what is related with the local aggregations of ceramic particles in the metal matrix and poor bonds between them.