Effect of Fe additions on the microstructures and room-temperature mechanical properties of Nb 16Si in-situ composites

Nb-16Si-xFe in-situ composites (x = 2, 4, 6, atom fraction(%), referred to 2Fe, 4Fe and 6Fe alloy, respectively, hereafter) were prepared by vacuum non-consumable arc-melting method and the effect of Fe additions on the microstructures and room-temperature mechanical properties of the Nb-16Si alloy was studied. The results reveal that the as-cast and heat-treated (vacuum annealing 100 h at 1350 ℃) 2Fe and 4Fe alloys are composed of Nb solid solution (Nb_SS), silicides of Nb₃Si and Nb₄FeSi, while the 6Fe alloy is composed of the Nb_SS phase and the Nb₄FeSi silicide. As the Fe content increasing, the volume fraction of the Nb₃Si phase decreases, while that of the Nb₄FeSi phase increases. Small silicde particles precipitate in the heat-treated Nb_SS phase. For the Nb₄FeSi, a new stiffening phase in the Nb-16Si alloy, its microhardness and fracture toughness are HV 1110 and 1.22 MPa·m^1/2, respectively. With the increasing of the atom fration of Fe from 2% to 6%, the room-temperature fracture toughness of the heat-treated alloys shows a decreasing tendency, while the hardness and compressive strength increase.