Ordering-induced Elinvar effect over a wide temperature range in a spinodal decomposition titanium alloy

Temperature-independent elastic modulus is termed as Elinvar effect, which is available by tuning the continuous spin transition of ferromagnetic alloys via composition optimization and the first-order martensitic transformation of shape memory alloys via plastic deformation. However, these reversible mechanisms are restricted generally in a narrow temperature range of less than 300 K. Here reports, by tuning a spinodal decomposition in a Ti-Nb-based titanium alloy via aging treatment, both the Elinvar effect in a wide temperature range of about 500 K and a high strength-to-modulus ratio of about 1.5% can be obtained by a continuous and reversible crystal ordering mechanism. The results demonstrate that the alloy aged at 723 K for 4 h has a nanoscale plate-like modulated beta+alpha" two-phase microstructure and its elastic modulus keeps almost constant from 100 to 600 K. Synchrotron and in-situ X-ray diffraction measurements reveal that the crystal ordering parameter of the alpha" phase increases linearly with temper-ature from 0.88 at 133 K to 0.97 at 523 K but its volume fraction keeps a constant of about 33.8%. This suggests that the continuous ordering of the alpha" phase toward the high modulus alpha phase induces a posi-tive modulus-temperature relation to balance the negative relation of the elastically stable beta phase. The aged alloy exhibits a high yield strength of 1200 MPa, good ductility of 16% and a high elastic admissible strain of 1.5%. Our results provide a novel strategy to extend the Elinvar temperature range and enhance the strength by tuning the crystal ordering of decomposition alloys.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.