Influence of Grain Size on the Corrosion and Wear Behaviour of HVAF-Sprayed Fe-Based Coatings

摘要

The current study investigates the influence of the grain size fraction D of a FeCrB/WC-Co feedstock material on the coating properties. In previous studies, novel FeCrB/WC-Co wear and corrosion protection coatings applied by means of high velocity air-fuel (HVAF) spraying were developed by the authors. It was observed that coatings, which were produced with a slightly decreased powder grain size fraction and identical chemical composition showed improved coating properties, i.e. reduced crack formation in the coating at high powder feed rates m and lower current densities at high overpotentials. The goal of this study is to investigate the influence of the powder grain size fraction on the coating properties in more detail. Furthermore, the underlying mechanism for the improved coating properties, with regard to their corrosion behaviour, is investigated. Therefore, the FeCrB/WC-Co feedstock material with the grain size fractions of -20 +3 μm and -32 +11 μm and identical chemical composition was applied by means of HVAF-spraying and the coatings were subsequently analysed. Light microscopy was used to investigate the microstructure of the coatings. The wear and corrosion properties were analysed using pin-on-disc (POD) and electrochemical polarization tests respectively. XRD-measurements were used to investigate the phase composition and to develop a hypothesis for the different corrosion behaviours of the investigated coatings. The results show that HVAF-sprayed FeCrB/WC-Co coatings produced with a powder grain size fraction of -20 +3 pm exhibit lower current densities at high overpotentials, compared to the coatings produced with a powder grain size fraction of -32 +11 μm.