Study on microstructure evolution and reaction mechanism of in-flight Ti–Si–C agglomerates during reactive plasma spraying using in situ water quenching

Abstract

An in situ water quenching method was used to explore the microstructure evolution and reaction mechanism of Ti–Si–C agglomerates during reactive thermal spraying. The quenched powders exhibit a melting process from outside to inside and small particles to large ones, forming complete droplets with increasing spray distance. The formation of the liquid phase is the basis of the reaction; once the liquid phase is formed, reactions begin to form new phases (TiC and Ti5Si3). The melting point of the new phase and the temperature of the droplet determine the formation mechanism and morphology of the new phase in the coating. As the melting point is higher than the droplet temperature, the new phase, TiC, grows to a large submicron size in flight. When the melting point is lower than the droplet temperature, like Ti5Si3, it dissolves into the liquid phase and re-precipitates in nanometer size at impact. Moreover, the droplet surface absorbed and dissolved O element from the atmosphere, and thus Ti3O coexisted with Ti5Si3 in lamellae of coatings.