The Mechanical and Tribological Properties of Cold-Sprayed Cermet Coatings—Al Alloy Substrate Systems

Abstract

The article describes the influence of a solid lubricant such as graphite on the coating-substrate adhesion, susceptibility to cracking during three-point bending tests and tribological properties of the cermet coating-substrate systems. Two types of deposits Cr3C2-25(Ni20Cr) and (Cr3C2-25(Ni20Cr))-5(Ni25C), cold-sprayed on the Al 7075 alloy substrate, were analyzed. The Cr3C2-25(Ni20Cr) coatings showed a homogeneous microstructure with evenly distributed ceramic particles in a Ni20Cr matrix. The (Cr3C2-25(Ni20Cr))-5(Ni25C) deposits also contained graphite placed both between metallic particles and near the crushed ceramic Cr3C2 particles. The force required for the crack that appeared in the coating-substrate system during the three-point bending test under constant velocity was significantly higher in the case of (Cr3C2-25(Ni20Cr))-5(Ni25C) deposit than in that without the solid lubricant. The cracks were observed perpendicular to the coating-substrate interface. The graphite embedded in the cermet coating structure prevented the formation of crack nuclei during three-point bending test under cyclic load at room temperature and reduced the size of cracks in the deposit at 200 °C. Both cermet coatings revealed the same adhesion. The addition of graphite not only did not deteriorate the adhesion of the deposits and thus their quality but also improved their other properties, such as flexural strength and wear resistance. Coatings containing the solid lubricant showed a lower wear index than the Cr3C2-25(Ni20Cr) deposits examined at both room and elevated temperatures. This recommends their use in industry as deposit working in heavy wear conditions. The presented results of mechanical tests effectively fill the gap regarding the properties of the cold-sprayed cermet coatings.