Zirconium modified Nb-22Ti-16Si alloys fabricated by laser additive manufacturing: Microstructure and fracture toughness

The microstructure and mechanical behavior of Nb-22Ti-16Si-xZr alloys (x = 0, 1, 5, 10, 15 at.%) were investigated by using laser solid forming (LSF) additive manufacturing from elemental powder mixture of Nb, Ti, Si and Zr. The as-deposited Nb-22Ti-16Si alloy presented a microstructure consisted of primary Nb-base solid solution (Nbss) dendrite and Nbss/(Nb)₃Si eutectic dendrites. The eutectic Nbss/γ-(Nb)₅Si₃ appeared with a morphology of lamellar structural feature when 1 at.%Zr was added, and its content increased with Zr content. Nbss/(Nb)₃Si eutectic dendrites disappeared when Zr content reaches 10 at.%. Further increasing of Zr (15 at.%) result in the appearance of a hypereutectic microstructure, which consisted by primary γ-(Nb)₅Si₃ and eutectic Nbss/γ-(Nb)₅Si₃. As the nominal Zr content increased, the fracture toughness of LSFed Nb-22Ti-16Si-xZr alloy increases first and reaches the maximum value (15.28 MPa m^1/2) in LSFed Nb-22Ti-16Si-5Zr alloy, and then decreases.