Development of novel carbon-free cobalt-free iron-based hardfacing alloys with a hard π-ferrosilicide phase

Abstract

Recently, iron-based alloys with a π-ferrosilicide phase have emerged as potential alternatives to cobalt-based hardfacing alloys. Here, we present the development of two π-ferrosilicide containing alloys: one with a ferritic matrix and the other with a ferritic-austenitic matrix. In the as-cast condition, both alloys revealed fine Ni- and Si-rich coherent cubic shaped D03 precipitates in the BCC matrix. The π-ferrosilicide phase was found to have an orientation relationship with the ferrite phase, nucleating within ferrite matrix and from ferrite grain boundaries. In contrast to carbide-strengthened hardfacing Fe-alloys, here the dissolution of the π-ferrosilicide phase at 1200 °C enables easy thermomechanical processing of these alloys, which results in refinement of the π-ferrosilicide and additional formation of χ-phase precipitates in the ferrite. Nano-scratch tests provided evidence of a resilient silicide-ferrite interface, likely to due to it possessing some coherency. Both alloys also displayed compressive strengths approaching 2 GPa and ductility in compression of approximately 25 %. The combination of processability and attractive mechanical properties suggests that these alloys have the potential to serve as alternatives to carbide-reinforced hardfacing Fe-alloys.