In situ composite coatings prepared by complex reactive plasma spraying of Fe2O3-Al-Cr2O3 composite powders

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.