Strain Glass State Research Articles

Strain glass in Ti50-x-yNi50+yNby alloys exhibiting a boson peak glassy anomaly

Strain glass, which is a type of ferroic glass with lattice strain short-range ordering, has been found in many shape memory alloy systems, while its unique properties still await to be investigated. Here we report a strain glass found in Ti50-x-yNi50+yNbx due to the synergistic effect of Ni and Nb atoms and its boson peak glassy anomaly. It is found that Nb atoms can only slightly suppress the martensitic transformation, but with the help of 1 at% excess Ni atoms (y=1), 2% Nb atoms (x=2) are enough to lead the system to the strain glass state. A three-dimensional phase diagram is established accordingly. Moreover, a boson-peak-like glassy feature is also found in the strain glass state, which resembles the boson peak in metallic glass. This work provides more clues to understand the glass nature of strain glass.

Ferroic glass behavior in (Bi,Na)TiO3-based lead-free electroceramics

Ferroic glass materials, that is, relaxors, spin glasses, and strain glasses attract special attention because of their intriguing physical properties and potential for novel technological applications. Here, several characterization techniques are used to demonstrate the occurrence of simultaneous relaxor and strain glass states in the ternary lead-free xBi0.5Na0.5TiO3-yBi0.5K0.5TiO3-zBaTiO3 (BNBK) system. Hysteresis and current density loops measurements at different temperatures for a BNBK ceramic showed typical characteristics observed in BNT based ceramics containing the tetragonal P4bm phase. Above 400 K, slim loops like those of ferroelectric relaxors are observed. A phase transition with simultaneous relaxor and strain glass character is revealed by the dielectric and anelastic characterizations, which opens up a wide spectrum of possible applications. The minimum of elastic modulus shifts to higher temperatures as the frequency increases, obeying the Vogel-Fulcher relation, which clearly shows the occurrence of a strain glass state in this material. Similar characteristics are observed in the imaginary part of the dielectric permittivity, which demonstrates the relaxor character of this phase transition. The origin of this phenomenon was elucidated with the help of structural characterizations, such as Raman spectroscopy and high-resolution synchrotron X-ray diffraction, at different temperatures. This work provides an in-depth understanding of the structural changes that determine the phenomenology behind the observed ferroic glass behavior and the ferroelectric, dielectric, and mechanical properties of this ternary ceramic composition.

Molecular dynamics simulations of ultralow hysteretic behavior in super-elastic shape memory alloys

Shape memory alloys (SMAs) that exhibit superelasticity with large recoverable strain and small hysteresis are in demand for practical applications, although their synthesis remains a challenge. We introduce metastable engineering to dope conventional SMA solid-solution atoms of relatively high concentration with "weak" local lattice distortion to realize ultralow hysteretic superelasticity. Large-scale molecular dynamic (MD) simulations of NiTi-based SMAs are performed to demonstrate how the presence of 2 ∼ 4 at.% Nb dopants lead to a stress-induced transition from a metastable pretransitional state to a strain-glass state. This is facilitated by a macroscopically homogeneous and continuous phase transformation in the course of superelastic loading and unloading. This spinodal decomposition-like phase transformation process endows SMAs with anhysteretic superelasticity that is insensitive to loading direction and grain size (below 15 nm). These findings show promise of achieving ultralow hysteretic superelasticity with large recoverable strain for SMAs.

Strain Glass State, Strain Glass Transition, and Controlled Strain Release

Strain glass is a new strain state discovered recently in ferroelastic systems that is characterized by nanoscale martensitic domains formed through a freezing transition. These nanodomains typically have mottled or tweed morphology depending on the elastic anisotropy of the system. Strain glass transition is a broadly smeared and high order–like transition, taking place within a wide temperature or stress range. It is accompanied by many unique properties, including linear superelasticity with high strength, low modulus, Invar and Elinvar anomalies, and large magnetostriction. In this review, we first discuss experimental characterization and testing that have led to the discovery of the strain glass transition and its unique properties. We then introduce theoretical models and computer simulations that have shed light on the origin and mechanisms underlying the unique characteristics and properties of strain glass transitions. Unresolved issues and challenges in strain glass study are also addressed. Strain glass transition can offer giant elastic strain and ultralow elastic modulus by well-controlled reversible structural phase transformations through defect engineering.

Strain states and unique properties in cold-rolled TiNi shape memory alloys

Martensitic transformation (MT), strain glass transition (SGT) and the corresponding stress-strain responses in cold-rolled Ti49.2Ni50.8 shape memory alloys (SMAs) at various amounts of cold-rolling deformation are investigated. A phase diagram describing all the strain states and transitions among them is established in the temperature – deformation space. It shows a normal sharp, strong first-order B2 to B19′ MT at low deformation levels (cold-rolling thickness reduction εp < 27%), but a continuous B2 to B19′ SGT at high deformation levels (εp ≥ 27%) upon cooling. Superelasticity with small hysteresis, tunable modulus and functional-fatigue resistance properties are achieved by altering the transition behavior from MT to SGT at εp ≥ 27%. Nanodomains of single variant B19′ martensite at the atomic scale are observed by using aberration-corrected scanning transmission electron microscopy in samples with εp = 27%. Further in-situ loading synchrotron-based high energy X-ray diffraction technique shows that the quasi-linear superelasticity associated with the SGT can be attributed to stress-induced continuous growth of B19′ nanodomains. Geometrical phase analysis of high-resolution transmission electron microscopy image reveals a nanoscale network of severe lattice distortion associated with the accumulated high-density of defects at εp ≥ 27%, which is the microstructural origin of the B19′ strain glass state. This work provides a detailed explanation for the longstanding puzzle of unique quasi-linear superelastic response in plastically deformed TiNi SMAs, and may shed light on achieving novel mechanical properties through defect engineering.

Strain glass state in Ni-rich Ni-Ti-Zr shape memory alloys

This work reports the existence of the strain glass state in Ni-rich Ni-Ti-Zr shape memory alloys induced by the precursor stages of the H-phase precipitation, typical of this alloy system. The strain glass is detected from dynamic mechanical testing and microstructural observations by electron diffraction and Transmission Electron Microscopy (TEM). The elastic modulus measurements also suggest the elinvar effect in these alloys. The strain glass state of this material exhibits superelastic effect in compression with recoverable strain levels over 4% and very little temperature dependence of the stress-strain curves over a temperature range of 230 to 300 K.

Nanocrystalline strain glass TiNiPt and its superelastic behavior

TiNi-based shape-memory alloys are known to exhibit a strain glass state under certain conditions, generally in the presence of high-density defects such as excess solute atoms or alloying elements, dislocations, and nanoprecipitates. In this paper, we report a strain glass transition in a nanocrystalline ${\mathrm{Ti}}_{50}{\mathrm{Ni}}_{35}{\mathrm{Pt}}_{15}$ alloy. The nanocrystalline strain glass state is achieved by a combined effect of high-density grain boundaries and high concentration doping of Pt atoms in the B2 matrix. The nanocrystalline ${\mathrm{Ti}}_{50}{\mathrm{Ni}}_{35}{\mathrm{Pt}}_{15}$ strain glass alloy showed a large near-complete progressive superelasticity with a recovery strain of about 6% and a low apparent Young's modulus of about 30 GPa in a wide temperature range of over 200 \ifmmode^\circ\else\textdegree\fi{}C. In situ synchrotron x-ray diffraction measurement showed that the strain glass B2 [B2(SG)] phase experienced B2(SG)\ensuremath{\rightarrow}R\ensuremath{\rightarrow}B19 transformation upon loading and B19\ensuremath{\rightarrow}B2(SG) upon unloading. The findings of this study provide insight for the development of nanocrystalline strain glass shape-memory alloys.

Kinetic arrest behavior in Ni-Co-Mn-Sn alloys within the phase boundary between martensite and strain glass

Kinetic arrest behavior is an interesting phenomenon that magnetic martensitic transition is suppressed during field cooling. A metastable “austenite” is arrested at very low temperatures upon withdrawing magnetic field after field cooling. However, why such a kinetically arrested “austenite” only appears in limited compositions has not been interpreted so far in ferromagnetic shape memory alloys. To settle this issue, the phase transforming properties and phase diagram of Ni37Co11Mn52-xSnx (x=8.5~10) system are explored. We found that kinetically arrested “austenite” is a special frozen strain glass state, which only appears within the martensite/strain glass phase boundary composition undergoing two-step transitions, i.e., austenite to strain glass and to martensite transition sequences. The appearance of kinetic arrest behavior is due to the comparative competition between the kinetic hindrance and martensitic driving force. The comprehensive understanding of the kinetic transforming properties of these ferromagnetic shape memory alloys is beneficial for tuning their functionalities.

Strain Glass and Novel Properties

Strain glass, a conjugate state to martensite, is emerging as an important concept in our understanding of martensitic materials. It resolves many puzzling phenomena, and potentially provides a mechanism for novel properties that are absent in conventional martensitic alloys. This article reviews the progress of strain glass research from its fundamental characterization to the interesting properties to which it leads. We first give a brief introduction of the origin and evidence of strain glass, showing nano-domains as the microscopic basis for understanding its properties. Then we demonstrate that the strain glass state can exhibit many unexpected properties such as a shape-memory effect, superelasticity with a narrow hysteresis over a wide temperature range, high damping and low modulus over a wide temperature, Invar and Elinvar effects, elastocaloric effects, and low-field-triggered large magnetostriction. Lastly, some remaining challenges and opportunities, as well as some ongoing works about the strain glass are discussed.

Coexistence of martensite and strain glass phases in homogenized Ni-rich TiNi shape memory alloys

The transport and thermal properties of homogenized Ti50-xNi50+x shape memory alloys (SMAs) in the range of 1.0 ≤ x ≤ 1.3 (in at. %) by means of electrical resistivity, Seebeck coefficient, thermal conductivity, and heat capacity measurements are presented. From the electrical resistivity measurement, we have observed thermal hysteresis in cooling and subsequent warming curves for x = 1.1 to 1.2 suggesting the occurrence of a martensitic transition. The martensitic transition is also detected in the Seebeck coefficient, thermal conductivity, and heat capacity measurements in these alloys. Despite this, the x = 1.2 alloy shows a negative temperature coefficient of resistivity over the entire temperature range under investigation, indicating the formation of strain glass phase at low temperatures. The existence of the strain glass state is confirmed by the frequency dispersion of the storage modulus measurement. These observations suggest a coexistence of martensite and strain glass phases in a well-controlled composition of the Ti50-xNi50+x system with 1.0 ≤ x ≤ 1.3. It is revealed that the crossover from martensite to strain glass in Ti50-xNi50+x SMAs is mediated via a coexisting of these two phases, which are triggered by a competing interaction between the thermodynamic and kinetic processes at low temperatures.

Mechanical relaxation and freezing in the room temperature strain glass alloy Ti50(Pd40Cr10)

The alloy Ti50(Pd40Cr10) undergoes a strain glass transition around room temperature evidenced by frequency dispersion of dynamic mechanical properties and lack of average structure change from that of the high symmetry austenite phase. However, since the strain glass transition is not a thermodynamic phase transition but a dynamic freezing process governed by the kinetics, a quantitative characterization of the slowing down of dynamics during the strain glass transition is still lacking. In the present study, the probability distribution function (PDF) of the relaxation time of the strain glass alloy is investigated spanning the whole transition temperature range (253 K–313 K). The slowing down of dynamics of the strain glass is indicated by the rapid increase of the characteristic relaxation time () upon cooling. The , as a function of temperature, shows a transition from Vogel–Fulcher relationship to an Arrhenius relationship. Such a change suggests two fundamentally different states: unfrozen strain glass state and frozen strain glass state. Furthermore, the spread of the PDF is connected to the fraction of quasi-static nanodomains, which helps the understanding of the dynamic freezing process in the strain glass.

Glassy Phonon Heralds a Strain Glass State in a Shape Memory Alloy.

Shape memory strain glasses are frustrated ferroelastic materials with glasslike slow relaxation and nanodomains. It is possible to change a NiCoMnIn Heusler alloy from a martensitically transforming alloy to a nontransforming strain glass by annealing, but minimal differences are evident in the short- or long-range order above the transition temperature-although there is a structural relaxation and a 0.18% lattice expansion in the annealed sample. Using neutron scattering we find glasslike phonon damping in the strain glass but not the transforming alloy at temperatures well above the transition. Damping occurs in the mode with displacements matching the martensitic transformation. With support from first-principles calculations, we argue that the strain glass originates not with transformation strain pinning but with a disruption of the underlying electronic instability when disorder resonance states cross the Fermi level.

Evolution of Intrinsic and Magnetic Field-Induced Magnetic Anisotropies in Strongly Phase-Separated Manganite Thin Films

Single crystalline thin film (∼ 100 nm) of La0.18Pr0.40Ca0.42MnO3 is grown on (001) oriented LaAlO3 substrates and the evolution of anisotropy associated with the supercooling behaviour of the magnetic liquid is studied as a function of temperature and magnetic field. The angle-dependent magnetization measurements ascertain that the easy magnetic axis lies in the plane of the film while the hard axis is along the plane normal. The ratio of the easy and hard axes magnetizations (M|| and M⊥) measured at 10 K, viz., M||/M⊥ (10 K) = 2.6, confirms the strongly anisotropic nature of the film. The easy axis ferromagnetic (FM) transition temperature (TC) is smaller than that along the hard axis. The giant hysteresis in FCC–FCW M–T, which manifests the magnetic liquid behaviour of the strongly phase-separated manganites is appreciably narrowed along the hard axis. The strain glass state is also less dominant along the easy axis. The analysis of the M–H data brings out that the easy axis remanence (Mr||) shows a nonlinear temperature dependence, while the one corresponding to the hard axis (Mr⊥) shows a nearly linear behaviour. The coercivity (HC) follows a law of the type \(H_{\mathrm {C}}\left (T \right )\mathrm {=}H_{\mathrm {C}}\mathrm {(0)(1-}{\text {AT}}^{b}\mathrm {)}\). The value of exponent b ∼ 0.5 for single-domain particles, but in the present case, the best fit to the experimental data yields the exponent b ≈ 0.25 for both HC|| and HC⊥. The smaller value of the exponent is attributed to the non-canonical nature of the ferromagnetic state and the associated strongly phase-separated nature of the LPCMO thin film.

Low-Field-Triggered Large Magnetostriction in Iron-Palladium Strain Glass Alloys.

Development of miniaturized magnetostriction-associated devices requires low-field-triggered large magnetostriction. In this study, we acquired a large magnetostriction (800ppm) triggered by a low saturation field (0.8kOe) in iron-palladium (Fe-Pd) alloys. Magnetostriction enhancement jumping from 340 to 800ppm was obtained with a slight increase in Pd concentration from 31.3 to 32.3 at. %. Further analysis showed that such a slight increase led to suppression of the long-range ordered martensitic phase and resulted in a frozen short-range ordered strain glass state. This strain glass state possessed a two-phase nanostructure with nanosized frozen strain domains embedded in the austenite matrix, which was responsible for the unique magnetostriction behavior. Our study provides a way to design novel magnetostrictive materials with low-field-triggered large magnetostriction.

Novel B19′ strain glass with large recoverable strain

We report a strain glass state (B19\ensuremath{'} strain glass) in a Ni-rich TiNi shape memory alloy produced by cold rolling. As compared to previously reported strain glasses, this strain glass state has outstanding properties including quasilinear superelasticity with a large recoverable strain (\ensuremath{\sim}4%), and slim hysteresis and high strength (\ensuremath{\sim}1.0 GPa) over a wide temperature range (\ensuremath{\sim}200 K). The existence of the B19\ensuremath{'} strain glass state is confirmed by (i) frequency dispersion of storage modulus, (ii) continuous decrease of electrical resistivity, and (iii) continuous growth of B19\ensuremath{'} nanodomains upon cooling. This study proves that the effect of defect strength on the creation of a strain glass state is in parallel to the effect of cooling rate on the creation of a structural glass, e.g., any strain crystal (i.e., martensite) can be turned into a strain glass if strong enough defects could be engineered.

The role of strain glass state in the shape memory alloy Ni50 +xTi50 −x: Insight from an atomistic study

Molecular dynamics simulations are performed to study the influence of Ni concentration on the phase transformations in Ni50+xTi50−x(0 ≤ x ≤ 2) alloys during thermal cycling between 100K and 500K. We successfully reproduce the experimental observations that the martensitic transformation temperature and the thermal hysteresis decrease with increasing Ni concentration when x ≤ 1.5, and the thermally induced martensitic transformation is prohibited when x > 1.5. Three types of martensitic twins are observed; increasing disorder from local distortion in martensitic variants is revealed with increasing Ni concentration at 100K. Furthermore, a strain glass state with disordered local lattice distortion exists when x > 1.5. In addition, it is found that the atomic distributions of the Ni-Ni and Ti-Ni pairs in strain glass can be significantly altered by temperature. Shape memory effect and pseudoelasticity in strain glass are also analyzed. It is found that the shape memory effect can be characterized by the transformation from frozen strain glass to the martensitic B191′twin and the following detwinning, while the pseudoelasticity can be characterized by the transformation from unfrozen strain glass to the B191′phase.

Sandwichlike strain glass phase diagram ofTi49Ni51−xPdx

Two kinds of phase diagrams can be observed in doped ferroic materials. A glass phase diagram is formed by doping a nontransforming end into a ferroic matrix, while doping a transforming end forms phase diagrams with a phase boundary separating two different ferroic phases. Here we report a phase diagram in which a strain glass state is sandwiched between two distinct ferroelastic phases. This type of phase diagram in doped ferroelastic materials bridges the one with a glass state and the one with a phase boundary. We thus establish a 3D phase diagram of ${\mathrm{Ti}}_{50\ensuremath{-}y}{\mathrm{Ni}}_{50+y\ensuremath{-}x}{\mathrm{Pd}}_{x}$ ternary alloys, in which the evolution of these different kinds of phase diagrams can be observed. An understanding from the Landau free energy landscape suggests that the transforming doping end plays three roles in influencing the ferroic matrix: (1) to destabilize the ferroic matrix phase, (2) to stabilize another ferroic phase different from the matrix one, and (3) to create random local fields. The competition between these effects determines various phase diagrams in doped ferroic materials. Thus our work may provide an experimental foundation for a unified mechanism to all three kinds of phase diagrams.

Defect strength and strain glass state in ferroelastic systems

It has been shown both experimentally and by computer simulations that stress-carrying defects can change a normal sharp first-order martensitic transformation (MT) to a continuous strain glass transition in ferroelastic systems and offer unique properties. However, strain glass state has been found only in limited ferroelastic systems with relatively small transformatoin strains such as the trigonal phase (1%) in NiTi-based alloys and the orthorhombic phase (2%) in TiNb-based alloys by means of impurity doping. We show in this paper that there exists a critical value of defect strength relative to the strength of MTs for creating a strain glass state. Using a typical strain glass system, Ti48.5Ni51.5 with symmetrical anti-site defects, as an example, we show that the equivalent Von Mises strain caused by anti-site defect with randomly distribution (with 3% concentration) is 7/8.9 times of that created by the stress free transformation strain of Martensitic phase in order to produce an R/B19 strain glass state respectively. The maximum interaction energy between the anti-site defects and the martensitic variant is estimated to be 16 times larger than that between different martensitic variants at this defect concentration. This finding may shed light on developing new strain glasses of much larger transformation strains for broader applications through defect engineering.

Strain glass state as the boundary of two phase transitions.

A strain glass state was found to be located between B2-B19’ (cubic to monoclinic) phase transition and B2-R (cubic to rhombohedral) phase transition in Ti49Ni51 alloys after aging process. After a short time aging, strong strain glass transition was observed, because the size of the precipitates is small, which means the strain field induced by the precipitates is isotropic and point-defect-like, and the distribution of the precipitates is random. After a long time aging, the average size of the precipitates increases. The strong strain field induced by the precipitates around them forces the symmetry of the matrix materials to conform to the symmetry of the crystalline structure of the precipitates, which results in the new phase transition. The experiment shows that there exists no well-defined boundary in the evolution from the strain glass transition to the new phase transition. Due to its generality, this glass mediated phase transition divergence scheme can be applied to other proper material systems to induce a more important new phase transition path, which can be useful in the field of phase transition engineering.

An in situ neutron diffraction study of anomalous superelasticity in a strain glass Ni43Fe18Ga27Co12 alloy

Superelastic behavior is traditionally related to the martensitic transition with a collective transformation scenario in some shape memory alloys. A kind of quasi-linear superelasticity accompanied by a finite avalanche or confined martensitic transformation was recently found in some alloy systems with strain glass state. Here, an in situ neutron diffraction technique was used to study the deformation behavior in an Ni43Fe18Ga27Co12 alloy with strain glass state in order to reveal the new intrinsic physical nature of the quasi-linear superelasticity. A significant modulus softening prior to the stress-induced martensitic transformation was observed during compression in the studied alloy, which is similar to the characteristics exhibited in the tweed precursor phenomena prior to temperature-induced martensitic transformation. Moreover, the diffraction peak broadening was further shown during the elastic stage of deformation for both single-crystal and polycrystalline samples, which mainly stems from the short-range fluctuation in the strain field inside each grain based on Williamson–Hall analysis. The authors believe that there exists a spatial heterogeneity in the modulus of the confined martensitic transformation alloy.