Superelasticity and Tunable Thermal Expansion across a Wide Temperature Range

Abstract

Materials that undergo a reversible change of crystal structure through martensitic transformation (MT) possess unusual functionalities including shape memory, superelasticity and low/negative thermal expansion. These properties have many advanced applications, such as actuators, sensors and energy conversion, but are limited typically in a narrow temperature range of tens of Kelvin.Here we report that, by creating a nano-scale concentration modulation via phase separation, the MT can be rendered continuous by an in-situ elastic confinement mechanism. Through a model titanium alloy, we demonstrate that the elastically confined continuous MT has unprecedented properties, © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 such as superelasticity from below 4.2 K to 500 K, fully tunable and stable thermal expansion, from positive, through zero, to negative, from below 4.2 K to 573 K, and high strength-to-modulus ratio across a wide temperature range. The elastic tuning on the MT, together with a significant extension of the crystal stability limit, provides new opportunities to explore advanced materials.

Nanoembryonic thermoelastic equilibrium and enhanced properties of defected pretransitional materials

“…27 Besides, the hypothesis that pretransition embryo growth explains or at least contributes to the invar effect is supported by experiments showing that a severe cold-work treatment can significantly change the thermal expansion behaviors. 19,[28][29][30][31] A second interesting effect of increasing the equilibrium ω upon cooling is a softening of the effective modulus. This softening counteracts the usual stiffening (increase of C 0 ) on cooling.…”

Characterisation studies of linear friction welded titanium joints

“…It should be pointed out that there are no twins in WCZ (if twins existed in WCZ, there would be high fractions near the misorientation angles of 65°and 85°in misorientation distribution) even in TMAZ near WCZ, which is different from the ECAP [27][28][29][30][31], cold rolling [36] and hot compression [37]. This is due to the high temperature at the interface and the heavy plastic deformation during LFW (see Table 2).…”

“…In this work, commercially pure titanium (CP-Ti) instead of α + β titanium alloy was chosen to examine the recovery and recrystallization behaviors, together with the texture development, in view of the complex effect of prior β on the final texture distribution in α + β titanium alloys [26,27]. It is accepted that dynamic recrystallization is hard to occur for pure titanium due to its greater stacking fault energy (0.31 J/m 2 [28]).…”

Weak fatigue notch sensitivity in a biomedical titanium alloy exhibiting nonlinear elasticity

“…It was forged at 1123 K into a bar with 55 mm in diameter and then rolled at 1073 K into a bar with 12 mm in diameter. The asrolled alloy has a single β phase microstructure with an average grain size of~5 μm and sub-grain size of~0.6 μm as well as a nanoscale Nb modulation with the domain size of 2-3 nm [20,24]. Three kinds of V-type circumferential notch specimens ( Fig.…”

“…Our recent investigations showed that Ti2448 contains a nanoscale spatial modulation of Nb, which is created by the isostructural phase decomposition, and an in-situ elastically confined martensitic transformation was proposed to explain its novel nonlinear elasticity [19]. This leads to some unprecedented properties such as strong in strength, soft in modulus, ductile in toughness in combination with super-elasticity and entirely tunable thermal expansion from positive, via zero, to negative in a wide temperature range [20,21]. The nanoscale Nb modulation can stabilize the β phase and cause a successive atomic rearrangement via the up-hill Nb diffusion [22,23].…”