Seynergistic effect of Mo and Zr additions on microstructure and mechanical properties of Nb-Ti-Si-based alloys additively manufactured by laser directed energy deposition

摘要

The synergistic effect of Mo and Zr additions on microstructure evolution,room-temperature fracture toughness and microhardness of Nb-22Ti-15Si-xMo-yZr(x=4,8,y=3,6)alloys manufactured by laser directed energy deposited(L-DED)have been investigated.The major phases in as-deposited 4Mo-3Zr alloy are Nb solid solution(Nbss),Nb_(3)Si andγ-Nb_(5)Si_(3).The Nb_(3)Si phases disappear with increasing Mo content to 8 at.%or increasing Zr content to 6%.γ-Nb_(5)Si_(3) precipitates formed in the Nbss of as-deposited xMo-yZr alloys due to the cyclic re-heating,and theγ-Nb_(5)Si_(3) precipitates and Nbss matrix exhibits orientation relationship(OR)of[001]Nbss//[1112]γand(110)Nbss//(0110)γin as-deposited 4Mo-6Zr alloy.The microstructure of xMo-yZr alloys became relative homogeneity and the Nbss matrix showed the better continuity after the heat treatment(1400°C/30 h).The Nb_(3)Si phase has transformed into Nbss andαNb_(5)Si_(3) with the OR have been determined as{100}Nbss//{100}αand{111}Nbss//{111}αin the heat-treated 4Mo-3Zr alloy.When Mo content increase to 8at.%,a part ofγ-Nb_(5)Si_(3) phase also transformed into theα-Nb_(5)Si_(3) phase with the OR have been determined as{1120}γ//{110}αand{1010}γ//{111}αafter heat treatment.Among the as-deposited alloys,the 4Mo-6Zr alloy has the highest fracture toughness KQ with the lowest hardness.The average KQ of 4Mo-6Zr and 8Mo-6Zr alloys increased by 28%and 30%after the heat treatment,and reached 13.61 and 11.43 MPa·m^(1/2),respectively.The hardness of Nb-22Ti-15Si-xMoyZr alloys is significantly decreased after the heat treatment.