The composite powders of the above two systems were prepared into coatings by plasma spraying. Fig. 1 shows the XRD patterns of the two systems coatings. According to Fig. 1a, the coating obtained by plasma spraying Ti-SiC composite powders were composed of TiC, Ti5Si3and SiC phases. According to Fig. 1b, the coating obtained by
plasma spraying Ti-SiC(ht) composite powders was mainly composed of TiC, Ti5Si3, and a small amount of SiC.It was found that TiC and Ti5Si3were formed by the reaction of Ti with SiC (reaction Eq. (3)) during plasma spraying. It can be obtained that Ti3SiC2was oxidized and decomposed into TiC and Ti5Si3according to Eq. (1) under the condition of plasmaspraying, and TiSi2was transformed into Ti5Si3phase through a series of intermediate phases (TiSi2→ TiSi→Ti5Si4→ Ti5Si3).
3Ti3SiC2+O2→4TiC +Ti5Si3+2CO(g) （1）
Zhou et al. also found that Ti3SiC2was difficult to exist in rapid non-equilibrium processes, such as reactive plasma spraying. The relative contents of TiC, Ti5Si3and SiC in the two composite coatings can be quantitatively analyzed by reference intensity ratio (RIR) of characteristic peaks. The calculation results show that the coating obtained by plasma spraying Ti-SiC composite powders contained TiC (35 wt%), Ti5Si3(42 wt%) and SiC (23 wt%). The coating obtained by plasma spraying Ti-SiC(ht) composite powders contained TiC (47 wt%), Ti5Si3(40 wt%) and SiC (13 wt%).
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