The microstructural characteristics and mechanical properties of Nb-16Si-22Ti-2Al-2Cr alloys with Zr addition

In this study, the effects of Zr addition on the microstructure and mechanical properties of arc melted Nb-16Si-22Ti-2Al-2Cr (at.%) alloy are investigated. Zr obviously promotes the eutectoid decomposition of Nb₃Si and formation of γ-Nb₅Si₃. The volume fractions of reticulate-like Nbss/α-Nb₅Si₃ eutectics and lamellar-like Nbss/γ-Nb₅Si₃ eutectics increase with Zr addition. The elastic modulus and nanohardness of constituent phases are changed by the Zr addition, which can affect the toughness of the alloys. The fracture toughness increases at Zr content of 2 at.% (14.15 MPa m^1/2); however, then drops with the increase in the Zr content from 4 to 8 at.%. Finally, the fracture toughness increases abnormally to 14.03 MPa m^1/2 when Zr content is up to 10 at.%. The high-temperature compression strength at 1200 °C decreases with increasing Zr content, but increases when the content of Zr is more than 6 at.%. The 10Zr alloy achieves a balance between room-temperature fracture toughness and high-temperature compression strength. Moreover, the orientation relationships between Nbss and Nb₅Si₃ change due to the addition of Zr and high-temperature compression.