Fabrication and characterization of heat and plasma treated SiC/Al2O3–YSZ feedstocks used for plasma spraying

Abstract

The SiC/Al2O3–YSZ (ZrO2 + 8 wt.% Y2O3) powders with different SiC particle sizes were fabricated and treated from spray drying, heat treatment, and plasma spraying. The morphology, phase composition, flowability and density of powders were analyzed. The sphericity and flowability of powders treated by plasma flame are increased greatly, and the particle surface is very smooth. The flowability and density of powder with nano SiC were evident better than those of powder with submicron SiC. The optimum flowability and compactness of powder with submicron SiC is obtained when the critical plasma spray parameter is 341 and 325, respectively. For nano size SiC, the optimum flowability and the maximum compactness of powders are obtained with critical plasma spray parameter of 341. The grain size of powders is increased after heat treatment and plasma spraying. The SiC is oxidized to SiO2 in the powders after heat treatment and plasma spraying. The Y2O3 dissolved from 8YSZ solid solution at higher critical plasma spray parameter. Besides, there is no phase transformation of ZrO2 for powders. The metastable phase of Al2O3 appeared in feedstocks with submicron SiC, but no metastable phase was formed in feedstocks with nano SiC particles, which nano SiC can hinder the formation of Al2O3 metastable phase. The densification process and mechanism of reconstituted particles used for plasma spraying were analyzed from surface morphology, cross section and simulation.