•Fe2O3-Al-Cr2O3 composite powders were complex reactive plasma sprayed.•Al-Fe2O3 reaction and Al-Cr2O3 reaction occurred in the same time in plasma jet.•The complex reactions influence the microstructure and properties of the coatings.•Large-sized metal particles were replaced by nano-sized metal particles.•Cr is beneficial for refining metal phase with increasing of Al-Cr2O3 proportion.Complex reactive plasma spraying (CRPS) was carried out by plasma spraying Fe2O3-Al-Cr2O3 composite powders. Two aluminothermic reactions, Al-Fe2O3 reaction and Al-Cr2O3 reaction, occurred at the same time in the plasma jet, and CRPS coatings were prepared. The effects of the complex reactions on the microstructure of the coatings were investigated by XRD, SEM and TEM. Hardness and toughness of the coatings were also evaluated. It was found that, compared to a single aluminothermic reaction (Al-Fe2O3 reaction), the phase composition of the CRPS coatings changed as follows: FeAl2O4 → Fe(Cr,Al)2O4 → FeCr2O4, α-Fe → α-(Fe,Cr), and Al2O3 → (Al0.9Cr0.1)2O3. The amount of metal phases increased, and large-sized metal particles were replaced by nano-sized metal particles uniformly dispersed in a ceramic matrix. Hardness and toughness of the coatings increased with increasing Al-Cr2O3 ratio in the composite powders. Nano-sized metal particles replaced large-sized metal particles and were uniformly distributed in the ceramic matrix resulting in the increase of hardness and toughness of the complex reactive plasma sprayed coatings.

Fe2O3–Al composite powders were deposited onto steel substrate by plasma spraying. The reaction products of the Fe2O3–Al composite powders in the plasma flame and their solidification process were investigated. The results showed that the reaction products of the Fe2O3–Al composite powders in the plasma flame were Fe–Al–O ceramic melt and Fe melt. Fe was not always formed in the reaction products of each composite particle, and the formation of Fe was dependent on the composition distribution and the reaction kinetics process of each composite particle. The composition inhomogeneity, discontinuity and porousness of the composite particles resulted in the difference of the reaction kinetics of each composite particle and the composition difference of the droplets. Hercynite solid solution, Fe, Al2O3 and FeAl phases were formed by non-equilibrium solidification of the Fe–Al–O ceramic melt. For the smaller size droplet, when it spread on the substrate, the spreading droplet was quickly chilled to form equiaxed grains with size of 100–200 nm. Nano-sized or submicron equiaxed grains, nano-sized columnar grains and cellular structure were formed in the larger spreading droplet. Fe rich hercynite solid solution nucleated and grew preferentially and then Al rich hercynite solid solution grew, which form composition segregation in the columnar grains. The main phases in the composite coating were hercynite solid solution.Highlights► The reaction products of Fe2O3–Al composite powders in plasma flame were Fe–Al–O ceramic melt. ► FeAl2O4, Al2O3 and FeAl were formed by non-equilibrium solidification of Fe–Al–O ceramic melt. ► The formation of Fe was dependent on the component distribution and reaction kinetics process of each composite particle. ► Fe rich hercynite solid solution (HSS) nucleated and grew preferentially, and then Al rich HSS grew.