NiCrAlY/ Al2O3 composite coatings were fabricated by micro-arc plasma spraying technology with internal
and external feedstock injection methods. The effect of powder infection method on the phase composition, microstructure
and dielectric properties was analyzed. Results show that: compared with the coatings prepared with external
feedstock injection method, the deposition efficiency of the coatings with internal feedstock method is higher and
the porosity of that is lower. Because of the completely melted α-Al2O3 particles, the coatings prepared with internal
feedstock injection method are mainly composed of γ/ γ′ and γ-Al2O3, and their microstructure is dense, the distribution
of NiCrAlY particles is uniform. The measurements of dielectric properties revealed that the real and imaginary
parts of the coatings with external feedstock injection method almost do not vary with frequency. However, the real
and imaginary parts of the coatings with internal feedstock injection method decrease with the increase of frequency,
which represents obviously frequency dispersion phenomenon.