Influence of Raw Materials Properties on the Development of Binary and Ternary S-HVOF Sprayed Ceramic Coatings with Tailored Compositions in the System Cr2O3-TiO2–Al2O3

The demand for multifunctional coatings in the Cr₂O₃-TiO₂-Al₂O₃ system disposing of improved hardness, wear and corrosion resistance is continuously growing. This combination of properties cannot be fulfilled by using only one powder; two or more oxide powders may be combined. For the conventional thermal spraying process, the availability of multi-system feedstock is limited. Suspension spraying satisfies these requirements by offering tailored compositions.

The influence of raw materials on the tailored aqueous binary suspensions in the Cr₂O₃-TiO₂-Al₂O₃ system and coating properties obtained by S-HVOF process was previously presented. For the preparation of ternary suspensions it was observed that these are particularly sensitive to each material properties, especially the particle sizes and surface properties, which strongly affect the suspensions stability. This effect was less evident for the binary suspensions. The approximation of the relationship particle sizes (d₅₀)/melting temperature for the different oxides seems to attenuate this effect.

The challenging of ternary suspensions reflects itself in the narrow processing window of the spray process in terms of process stability and coating efficiency, as well as in the coating properties. The gain in coating functionality versus the spray stability needs to be considered for each application upon the choice between tailored binary and ternary suspensions.