Phase and structure formation mechanisms of SHS synthesized composite coatings

High performance composite coatings were synthesized by self-propagation high-temperature synthesis followed by gravitational-separation process based on thermite reaction. The phase, structure and composition of generated composite coatings were investigated, and formation mechanism was studied by thermodynamic analysis. Results showed that phase composition of Al-Fe2O3 reaction system consisted of Al2O3, Fe and FeAl2O4. In Al-Fe2O3/Al-Cr2O3 composite reaction system, Fe-Cr alloy was formed and FeAl2O4 phase disappeared, which could improve the corrosion resistance of composite coatings. Furthermore, the addition of SiO2 in SHS reaction favored the formation of low-melting point phase Al2O3·SiO2, which filled into voids of Al2O3 dendrites and reduced the porosity of composite coatings, thus improving their strength and densification level. Moreover, the generated transition structure in different reaction systems could buffer the residual stress to promote the binding between the composite coating and steel pipe.