Microstructure and thermal conductivity of Fe-based amorphous coatings prepared by HVOF thermal spraying

Gas-atomized Fe₅₉Cr₁₂Nb₅B₂₀Si₄ amorphous powders were deposited to form amorphous coatings on the ASTM 4032 aluminum alloy substrate by HVOF thermal spraying under different conditions. The microstructural studies show that the coatings exhibit dense layered structure and relatively low porosity, less than 1.3 %. The coatings primarily consist of amorphous matrix with some precipitated nanocrystals, and the amorphous fractions of all the coatings are more than 40% by calculation from DSC results. Depending on the structure advantage, the coatings exhibit high microhardness, from 1230 HV to 1285 HV. Meanwhile, the bonding strength of as-deposited coatings increases with the rising flow of oxygen and kerosene, reached to 53.3 MPa. The ability of heat transport of asdeposited Fe-based coatings were investigated by calculation thermal conductivities from k= apC_p. The results show that the thermal conductivity ascends slightly with the enlargement of spraying parameter in examined range, from 1.99 to 3.1 W/mK. However, thermal conductivities of all designed coatings are lower than metal-based materials. Furthermore, it is also notable that the microstructural characteristic and performance of the Fe-based coatings under different spraying conditions are similar, which manifests the Fe₅₉Cr₁₂Nb₅B₂₀Si₄ powder has a great broad adaptability for HVOF thermal spraying process. It is very important for practical engineering applications.