Microstructure and Phase Composition of Composite Coatings Formed by Plasma Spraying of ZrO_2 and B_4C Powders

摘要

The effect of addition of 5 to 30 wt.% boron carbide (B_4C) on structure and hardness of plasma sprayed zirconia (ZrO_2) coating has been studied in this paper. The coatings have exhibited a uniform porous microstructure. A reaction between B_4C and ZrO_2 resulted in the formation of a diboride (ZrB_2) phase. The presence of ZrB_2 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 ZrB_2 was observed in the case of 15 wt.% B_4C addition. Hardness of the coatings have been influenced by the porosities, additionally generated by the formation of ZrB_2. Under increased hydrogen flow rate, a composite coating of ZrO_2-ZrB_2 was obtained from the ZrO_2-B_4C powder mixture.