Influence of equiatomic Zr/Nb substitution on superelastic behavior of Ti-Nb-Zr alloy

Based on a binary Ti-26Nb (at%) alloy, Ti-(26-z)at% Nb-(z)at% Zr (z=2, 6, 8 and 10) alloys via equiatomic substitution of Nb by Zr are formulated. Influence of equiatomic Zr/Nb substitution on microstructure evolution, mechanical properties and deformation mechanism of the superelastic Ti-Nb-Zr alloy are investigated. Experimental results show that the phase constitution is single beta phase or beta/omega(ath) phase at 0 < Zr/Nb < 0.35 since the measured Ms temperature is maintained at around 250 K. The two-phase microstructure consist of alpha '' martensite and beta phase is obtained at Zr/Nb ratio > 0.4 due to the attenuation of beta stabilizing effect of Zr, which is related closely to the Nb content in ternary Ti-Nb-Zr alloys. The mechanism of the superelastic behavior alters gradually from reversible beta/alpha '' martensitic transformation to rearrangement of pre-existing alpha '' martensites as a function of Zr/Nb ratio increase. At Zr/Nb=0.3, the alloy of corresponding composition exhibits the best superelasticity and combined mechanical performance. A coefficient of Delta T (Delta T=T-beta-Ms) is proposed to understand the experimental results by evaluating the beta instability of Ti-Nb-Zr alloys. (c) 2012 Elsevier B.V. All rights reserved.