Mechanical properties and microstructure evolution of NbSiZr based alloy

Abstract

To improve the mechanical properties of Nb-Si-Zr based superalloys at room temperature, the effect of a trace amount of Cr, C, Hf, Ta and Sc elements on the solidification processes, phase composition, mechanical properties and fracture behavior of Nb-Si-Zr based superalloys are studied by vacuum non-consumable arc-melting. The results show that the based alloy consists Nbss phase, γ-(Nb,X)5Si3 phase and Zr-rich γ-(Nb,X)5Si3 phase. However, there is no Zr-rich γ-(Nb,X)5Si3 phase in 20Zr-2C and 20Zr-4Hf alloys, indicating that a trace amount of C or Hf elements accelerates the diffusion of Zr element, and improves the segregation of the Nb-Si-Zr based alloys for the later stage of the superalloy solidification. The Nbss fraction in the matrix alloy (20Zr alloy) is 60%. C element increases the Nbss phase fraction by 4%, and Cr and Sc elements reduce the Nbss phase fraction by 4% and 6%, Hf and Ta elements reduce the Nbss phase by 1% and 2% compare with the matrix alloy (20Zr alloy). C element is dissolved in Nbss phase and γ-(Nb,X)5Si3 phase, while Cr element is more dissolved in Nbss phase and Sc element is more dissolved in Zr-rich γ-(Nb,X)5Si3 phase. The toughness of 20Zr-2 C alloy is the highest, and its KQ value reaches 14.05 MPa·m1/2, compared with the matrix alloy (20Zr alloy) increased by 23.46%. The enhancement of Nbss phase fraction and petal shaped microstructure make the crack propagation more difficult, thus increasing the KQ value of the 20Zr-2C alloy. The compressive properties of 20Zr-4Cr alloy are the best, and its compressive strength reaches 1807.3 MPa, compared with the matrix alloy (20Zr alloy) increased by 17.09%. The reason is that a trace amount of Cr element increases the fraction of γ-(Nb,X)5Si3 phase.