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

Abstract

To reduce the adverse effects of highly active titanium elements in NbSi alloy, a series of high content of Zr and Zr for Ti substitution in NbSi 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 = 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 alloys, resulting in the effect of significant solution strengthen. In 24Ti16Zr alloys, three-types of Nbss/Nb5Si3 eutectic are found, resulting in large supercooling degree and rapid cooling condition. The maximum KQ value and compressive strength are 12.47 MPa·m1/2 and 1800 MPa respectively in 24Ti16Zr alloys. The KQ values in Nb-16Si-(24-x)Ti-xZr (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 eutectic. The high-temperature compressive strength is also prepared (1200 °C), element Zr can provide a signally work hardening by making a strong cooperative deformation of Nbss and γNb5Si3 phases, and the highest true stress values are found in 8Ti16Zr alloys.