Microstructure, mechanical and tribological characteristics of plasma, detonation gun and HVOF sprayed NiCr/Cr3C2-BaF2•CaF2 coatings

The microstructure, mechanical properties and tribological behaviour of NiCr/Cr3C2-BaF2 center dot CaF2 composite coatings prepared with atmospheric plasma spraying, detonation gun spraying (DS) and high velocity oxyfuel spraying (HVOF) technologies were systematically investigated. X-ray diffraction and transmission electron microscopy analyses showed that the main phases of the three kinds of NiCr/Cr3C2-BaF2 center dot CaF2 coatings were mainly consistent with the designed feedstock powders. The three kinds of NiCr/Cr3C2-BaF2 center dot CaF2 coatings have similar and high microhardness. The HVOF and DS NiCr/Cr3C2-BaF2 center dot CaF2 coatings have lower porosity and higher adhesive strength in comparison to the plasma sprayed NiCr/Cr3C2-BaF2 center dot CaF2 coating. The friction coefficients of the HVOF and DS coatings were lower than that of the plasma sprayed coating, and the HVOF and DS coatings showed better wear resistance. The lower friction coefficients and wear rates of the three coatings and coupled Si3N4 balls at elevated temperatures were attributed to the formation of a compact BaF2 center dot CaF2 eutectic lubricating layer on the worn surface.