Effects of Phosphorus and Carbon Contents on Amorphous Forming Ability in Fe-based Amorphous Alloys Used for Thermal Spray Coatings

Cost-effective Fe-based amorphous alloys used for thermal spray coatings were developed by varying contents of P and C, and their microstructure, hardness, and corrosion resistance were analyzed. In order to achieve chemical compositions having high amorphous forming ability, thermodynamically calculated phase diagrams of Fe-Al-P-C-B five-component system were used, from which compositions of super-cooled liquid having the lowest driving force of formation of crystalline phases were obtained. The thermodynamic calculation results showed that only phases of Fe 3 P and Fe 3 C were formed in the Fe 78 Al 2 P (18.3− x ) C x B 1.7 alloy system. Considering driving force curves of Fe 3 P and Fe 3 C, the carbon contents were selected to be 6.90 and 7.47 at. pct, when the thermodynamic calculation temperatures were 697 K (414 °C) and 715 K (442 °C), respectively. According to the microstructural analysis of suction-cast alloys, the Fe 78 Al 2 P 10.83 C 7.47 B 1.7 alloy showed a fully amorphous microstructure, whereas the Fe 78 Al 2 P 11.40 C 6.9 B 1.7 and Fe 78 Al 2 P 10.3 C 8.0 B 1.7 alloys contained Fe 3 P and Fe 3 C phases. This Fe 78 Al 2 P 10.83 C 7.47 B 1.7 alloy showed the better hardness and corrosion resistance than those of conventional thermal spray coating alloys, and its production cost could be lowered using cheaper alloying elements, thereby leading to the practical application to amorphous thermal spray coatings.