Fabrication and properties of thermal sprayed stainless steel-based nanocomposite coatings

Stainless steel-based feedstock powders with nano-iron oxide particles (from direct addition and thermal oxidation) were prepared by ball milling and oxidation process, respectively. It was found that iron oxide nanoparticles were on the surface of stainless steel powders in the form of particulates (deliberate addition of magnetite and hematite) or nanoplatelets (thermal oxidation). The powders were thermal sprayed by low velocity oxy-fuel (LVOF) technique. The stainless steel-based coatings had the typical thermal spray microstructure, including splats, oxide layers, unmelted particles and pores. There were no nanoparticles seen in the microstructure due to complete oxide melting at the flame spray temperature and iron oxide in all coatings was in the form of hematite. Considering physical properties, porosity was decreased when there were second phase nanoparticles and thickness was very similar except the coating with hematite addition. Hardness of the coatings was slightly increased when incorporating with iron oxide nanoparticles. Sliding wear rate and friction coefficient of the nanocomposite coatings were lower than that of the pure stainless steel. Iron oxide nanoparticles could improve hardness and sliding wear resistance in the stainless steel-based coatings due to an increasing amount of iron oxide in the coatings.