Microstructure and Phase Composition of Composite Coatings Formed by Plasma Spraying of ZrO2 and B4C Powders

The effect of addition of 5 to 30 wt.% boron carbide (B₄C) on structure and hardness of plasma sprayed zirconia (ZrO₂) coating has been studied in this paper. The coatings have exhibited a uniform porous microstructure. A reaction between B₄C and ZrO₂ resulted in the formation of a diboride (ZrB₂) phase. The presence of ZrB₂ in the coatings has been confirmed through x-ray diffraction studies. In order to study the effect of critical processing parameters, the coatings have also been deposited under increased hydrogen flow rate (11.8 SLM). This increased the abrasion integrity of the coatings. A high yield of ZrB₂ was observed in the case of 15 wt.% B₄C addition. Hardness of the coatings have been influenced by the porosities, additionally generated by the formation of ZrB₂. Under increased hydrogen flow rate, a composite coating of ZrO₂-ZrB₂ was obtained from the ZrO₂-B₄C powder mixture.