Synergistic effect of Zr and Ti on microstructure and properties for Nb-Si based in-situ composites

To reduce the adverse effects of highly active titanium elements in Nb-Si - Si alloy, a series of high content of Zr and Zr for Ti substitution in Nb-Si - Si based alloys are studied. The results show that the addition of Zr changes the solidification path from hypoeutectic to eutectic. The fracture toughness significantly enhances in 24Ti-xZr x Zr (x x = 0, 4, 8, 16) alloys, owing to the increase of Nbss phases and microstructure refinement in the matrix. Moreover, the room-temperature compression properties increase in 24Ti-xZr x Zr alloys, resulting in the effect of significant solution strengthen. In 24Ti-16Zr - 16Zr alloys, three-types of Nbss/Nb5Si3 5 Si 3 eutectic are found, resulting in large supercooling degree and rapid cooling condition. The maximum KQ Q value and compressive strength are 12.47 MPa & sdot;m1/2 1/2 and 1800 MPa respectively in 24Ti-16Zr - 16Zr alloys. The KQ Q values in Nb-16Si-(24-x)Ti-xZr x )Ti- x Zr (x x = 4, 8, 16, 24) alloys enhance with element Zr increases to 16 at.% and then decline slightly, suggesting that appropriate substitution of Zr for Ti is effective for promotion of toughness. It's owing to the formation of complex Nbss/(Nb, X)5Si3 5 Si 3 eutectic. The high-temperature compressive strength is also prepared (1200 degrees C), element Zr can provide a signally work hardening by making a strong cooperative deformation of Nbss and gamma Nb5Si3 5 Si 3 phases, and the highest true stress values are found in 8Ti-16Zr - 16Zr alloys.