The effect of Mo on microstructure and mechanical properties of Nb-22Ti-16Si alloy additively manufactured via laser directed energy deposition

Alloying process and processing optimization are most effective methods to modify the microstructure and mechanical properties of Nb-Si based alloys. In this work, Nb-22Ti-16Si-xMo(x = 5–20 at%) alloys were successfully fabricated by a laser directed energy deposition additive manufacture with elemental powder mixtures. The effect of Mo on the microstructure, micro-hardness, nano-hardness and fracture toughness of Nb-22Ti-16Si-xMo alloy were investigated. The results indicated that the addition of Mo in Nb-22Ti-16Si alloy is promoting the formation of Ti(Nb)5Si3 and β-Nb5Si3 phases and inhibiting the formation of Nb3Si phase. Mo was preferentially enriched in the niobium solid solution (Nbss) phase. The volume fraction of Nbss phase first increases then slightly decrease, while Ti(Nb)5Si3 phase was increased with Mo content, especially Nbss matrix also become more continuous. The solidification path of Nb-22Ti-16Si-xMo alloys show a certain deviate from the prediction by the Scheil solidification models. Mo alloying in Nb-22Ti-16Si alloy also lead to the increase in the young’s modulus and nano-hardness of Nbss and β-Nb5Si3 phases. The fracture toughness of Nb-22Ti-16Si-xMo(x = 5–20 at%) alloys first increases to 12.2 MPa m1/2 when Mo content increases to 10 at%, then decreases with further increases in Mo content, while their micro-hardness shows the opposite trend.