Microstructure and mechanical properties of TiB₂-Ni composite coating

The TiB₂-Ni composite powder feedstock was fabricated by agglomeration and sintering method. This powder was used to deposit TiB₂-Ni coating by two thermal spray technologies, atmospheric plasma spray(APS) and high velocity oxygen fuel spray(HVOF). The microstructure, phase constitution, porosity, hardness and fracture toughness of two sprayed TiB₂-Ni coatings were compared and analyzed. The results showed that the HVOF sprayed TiB₂-Ni coating had more compact structure, larger TiB₂ content, higher hardness and better fracture toughness than the APSed coating. The TiB₂ in two coatings had no obviously deboronization and oxidation. However, the TiB₂ in APS process was dissolved in metallic phase to form a large number of brittle Ni₂₀Ti₃B₆ phases. This dissolution reaction reduced the TiB₂ content in coating and it was the main reason for the lower hardness and worse fracture toughness of APSed TiB₂-Ni coating.