Microstructure and mechanical properties of Cr3C2-25(Ni20Cr) cold sprayed cermet coatings containing Ni-graphite

The cermet coatings are one possibility of modifying materials surface to enhance their durability and properties required in different applications. The present paper concentrates on Cr₃C₂-25(Ni20Cr) cermet coatings containing a Ni-graphite (graphite particles clad in a nickel sheath) as the solid lubricant. The coatings were sprayed on the Al 7075 alloy by means of high-pressure cold spray system Impact Innovations 5/8 using commercial Cr₃C₂-25(Ni20Cr) and Ni-graphite powders. The influence of the Ni-20 graphite and Ni-40 graphite powders on the microstructure (phase composition, porosity, adhesion and cohesion of particles, amount of incorporated ceramic particles), surface topography and mechanical properties (microhardness, Young’s modulus) of the as-sprayed cermet coatings was investigated. The microstructure of the as-sprayed coatings was characterized in macro-, micro-, and nanoscale both near the coating-substrate interface, and the coating using X-ray diffraction technique as well as the scanning and transmission electron microscopy. The coatings were composed of hard carbide particles (Cr₃C₂) and solid lubricant particles (Ni-graphite) embedded in the matrix (Ni20Cr). The surface topography of the as-sprayed cermet coatings was determined using a non-contact profiler, whereas mechanical properties of coatings were evaluated by micro-indentation and Vickers microhardness.

Acknowledgments

This work is supported by National Science Centre, Poland (Project No 2017/25/B/ST8/02228).