In the plasma spraying process, the powders with good fluidity andhigh density were more favorable to obtain the high-quality coating. Spray drying is an effective method to obtain powders with good fluidity and high density. Spray drying technology can make direct contact between the raw material powders so as to facilitate rapid melting and reaction to form uniform and dense coating under the action of plasma jet. Heat treatment can make the composite powder of spray drying have higher density and cohesive strength.
Fig. 1shows the SEM micrographs and EDS results of Ti-SiC and Ti-SiC(ht) composite powders. It can be observed from Fig. 1a the composite powders prepared by spray drying were spherical or near spherical particles which were suitable for plasma spraying. It can be seen from Fig. 1c that Ti-SiC composite powders were formed by coating the smaller SiC particles around the larger Ti particles. It can be seen from Fig. 1b that a small part of the powders adheres together after heat treatment at 1200 °C. Compared with Fig. 1c and d, it was found that after 1200 °C heat treatment, the sphericity of composite powders slightly decreases and the surface roughness increases. It may be due to the disappearance of residual moisture and binder in the composite powders after heat treatment at 1200 °C, and the solid phase diffusion reaction between Ti and SiC particles. It can be seen from Fig. 1e and f that the element composition of the composite powders of the two systems were Ti, Si and C, and no impurities appeared.
Fig. 1. SEM micrographs and EDS results of Ti-SiC and Ti-SiC(ht) composite powders: (a) Ti-SiC, (b) Ti-SiC(ht), (c) high magnification of (a), (d) high magnification of (b), (e) EDS result of region A in (c) and (f) EDS result of region B in (d).
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