Thermally Sprayed Amorphous and Nanostructured Iron-Based Coatings with Particle Reinforcement

Thermal spraying of amorphous iron-based alloys has become more and more common in the last years. Besides their good corrosion behavior, such coatings are well-known for high hardness and good resistance against abrasive wear. However, as regards the microstructure, these materials do not reach the performance of typical cermets such as WC-Co or CR₃C₂-Ni20Cr. To enhance their properties, amorphous iron-based coatings are reinforced with hard particles which are of the same type like the precipitations in the metal matrix. For this purpose, the powder is modified by high-energy ball milling and sprayed by means of HVOF and APS. The resulting coating properties are correlated to the chemical composition of the feedstock and the process parameters. While HVOF is used to transfer the microstructure of the powder into the coating, APS leads to a re-melting of the powder particles, whereby hard phases react as solidification nuclei. Due to the different process characteristics, the mechanical coating properties differ significantly. Specific values for microhardness and porosity as well as wear and corrosion resistance are given for coatings produced with different chemical compositions and process parameters.