Stress-induced Phase Transition Research Articles

Mechanisms of strength–plasticity enhancement and stress-induced phase transition in a medium-carbon low-alloy steel

Mechanisms of strength–plasticity enhancement and stress-induced phase transition in a medium-carbon low-alloy steel

Self-encapsulated ionic fibers based on stress-induced adaptive phase transition for non-contact depth-of-field camouflage sensing

Ionically conductive fibers have promising applications; however, complex processing techniques and poor stability limit their practicality. To overcome these challenges, we proposed a stress-induced adaptive phase transition strategy to conveniently fabricate self-encapsulated hydrogel-based ionically conductive fibers (se-HICFs). se-HICFs can be produced simply by directly stretching ionic hydrogels with ultra-stretchable networks (us-IHs) or by dip-drawing from molten us-IHs. During this process, stress facilitated the directional migration and evaporation of water molecules in us-IHs, causing a phase transition in the surface layer of ionic fibers to achieve self-encapsulation. The resulting sheath-core structure of se-HICFs enhanced mechanical strength and stability while endowing se-HICFs with powerful non-contact electrostatic induction capabilities. Mimicking nature, se-HICFs were woven into spider web structures and camouflaged in wild environments to achieve high spatiotemporal resolution 3D depth-of-field sensing for different moving media. This work opens up a convenient route to fabricate stable functionalized ionic fibers.

An atomistic study of effects of temperature and Ni element on the phase transition and wear behavior of NiTi shape memory alloy

Phase transition and tribological behavior of NiTi alloys have drawn great attention. Molecular dynamics simulation was adopted to investigate the effects of temperature on the mechanical behavior and variant formation of NiTi, as well as its wear behavior. Thermally and stress-induced phase transition behavior of NiTi alloys were studied. It is found that residual austenite phase boundaries during martensitic phase transformation could inhibit martensitic phase transition, changing the phase transition temperatures, and the mechanical properties of NiTi. Wear behavior of single-crystal NiTi with a wide temperature domain and content was studied. The optimal wear resistance of NiTi was at 300 K during cooling. Appropriate improvement in Ni content is beneficial to the formation of martensite variants and enhancement of the wear resistance.

Shear stress induced phase transitions of cubic Eu2O3 under non-hydrostatic pressures

Pressure-induced phase transitions in cubic Eu2O3 subjected to non-hydrostatic conditions have been studied by in situ high-pressure synchrotron angle dispersive x-ray diffraction and Raman scattering measurements up to 30.1 and 43.8 GPa, respectively. Both x-ray diffraction and Raman spectroscopy results indicate that the pressure-induced transition routines of cubic Eu2O3 depend on the nature of stress loading. In contrast to our previous high-pressure studies of cubic Eu2O3 under hydrostatic pressure, where cubic Eu2O3 transforms directly into a hexagonal structure, the x-ray diffraction data show that cubic Eu2O3 begins to transform into the monoclinic phase at a non-hydrostatic pressure of about 4.3 GPa, while the monoclinic to hexagonal phase transition is initiated at about 6.4 GPa. These phase transitions have also been confirmed by Raman spectroscopy; the hexagonal phase is stable up to at least 43.8 GPa; and the material decompressed from high pressures is composed of a monoclinic phase, showing that the cubic Eu2O3 to monoclinic phase transition is irreversible due to the constructive nature. Pressure coefficients of Raman peaks and Grüneisen mode parameters of cubic, monoclinic, and hexagonal phases followed under pressure were determined. Furthermore, this study provides evidence for the shear stress-induced cubic to monoclinic phase transition in cubic Eu2O3 and the corresponding mechanism.

Stress-Induced Structural Phase Transition in Polystyrene/NaYF4: Eu3+ Photoluminescent Electrospun Nanofibers

Polystyrene (PS) composite nanofibers were successfully fabricated by embedding NaYF4: Eu3+ nanophosphor into the PS matrix via electrospinning. The photoluminescence spectra, surface morphology and crystal structure of nanofibers were characterized by photoluminescence spectroscopy, scanning electron microscopy, and X-ray diffractometer, respectively. Stress-induced α-NaYF4: Eu3+ (cubic) to β-NaYF4: Eu3+(hexagonal) structural phase transformation was observed in the nanofibers. The stress-induced phase transformation provides enough space for tailoring the properties of novel nanostructures. The composite nanofibers exhibited blue emission with 239 nm excitation wavelength. The XRD pattern of espun nanofibers confirmed the successful incorporation of 5% NaYF4: Eu3+ nanophosphors into the PS matrix. Brilliant values of the chromaticity coordinates of the prepared photoluminescent nanofibers (PLNs) predict their possible use in blue solid-state lighting applications.

Landau theory of ferroelastic phase transitions: Application to martensitic phase transformations

The peculiarities of two Landau-type theories of ferroelastic phase transitions have been analyzed. The predictions of both theories have been compared with well-known experimental data obtained for the shape memory alloys (SMAs) undergoing the first-order martensitic transformations (MTs). It has been shown that the predictions of the Landau–Devonshire theory, which disregards the third-order term in power expansion of Gibbs free energy, contradict the experimental data, while the results of the symmetry conforming Landau theory, which takes into account this term, are in agreement with experimental data. The impossibility of occurrence of the second-order MT is demonstrated starting from the thermodynamic definition of the second-order phase transition. It is argued that the stress–strain loops, obtained for SMAs, can imitate the stress-induced phase transition in the absence of such transition.

Birefringence Imaging-Based Investigation of Stress-Induced Phase Transitions in SrTiO3

The spatial distributions of ferroelectric and structural phase transitions in quantum paraelectric SrTiO3 under uniaxial stress were microscopically observed using birefringence imaging techniques.

Thermal diffusivity of organosuperelastic soft crystals during stress-induced phase transition

Thermal diffusivity during stress-induced phase transition was examined and precisely determined in terephthalamide, an organosuperelastic soft crystal. A 14% maximum change in thermal diffusivity was realized in a superelastic phase transformation at a shear stress below 0.5 MPa. Thermal diffusivity measurements under the crystal deformation were achieved using microscale photothermal temperature-wave analysis. A maximum fivefold anisotropy was found in the thermal diffusivity between the c axis and other crystal axes. The results indicate the potential for developing practical thermal applications of organosuperelastic single crystals.

Shape memory effect in metallic glasses

Shape memory effect in metallic glasses

Stress-induced phase transitions in nanoscale CuInP2S6

Using Landau-Ginsburg-Devonshire approach and available experimental results we reconstruct the thermodynamic potential of the layered ferroelectric CuInP$_2$S$_6$ (CIPS), which is expected to be applicable a wide range of temperatures and applied pressures. The analysis of temperature dependences of the dielectric permittivity and lattice constants for different applied pressures unexpectedly reveals the critically important role of the nonlinear electrostriction in this material. With the nonlinear electrostriction included we calculated temperature and pressure phase diagrams and spontaneous polarization of bulk CIPS. Using the coefficients of the reconstructed four-well thermodynamic potential, we study the strain-induced phase transitions in thin epitaxial CIPS films, as well as the stress-induced phase transitions in CIPS nanoparticles, which shape varies from prolate needles to oblate disks. We reveal the strong influence of the mismatch strain, elastic stress and shape anisotropy on the polar properties and phase diagrams of nanoscale CIPS. Also, we derived analytical expressions, which allow the elastic control of the nanoscale CIPS polar properties. Hence obtained results can be of particular interest for the strain-engineering of nanoscale layered nanoferroelectrics.

Properties of stress-induced super tetragonal phase in epitaxial BiFeO3 thin film

Stress-induced structural phase transitions in multiferroic BiFeO3 thin films have attracted much attention for both fundamental research and promising applications in electronic devices. In this work, with the assistance of spherical aberration-corrected transmission electron microscopy, a tetragonal phase with the super large tetragonality (c/a ∼ 1.53) was found in the epitaxial BiFeO3 thin film on a LaAlO3/Si substrate. Analyses of atom positions showed that displacements of an Fe atom in this super tetragonal phase are much smaller than that in a regular tetragonal phase. First-principles calculations revealed that the structural phase transition occurs with the increasing lattice tetragonality c/a, accompanied by transitions in the atomic coordination and magnetic order.

Crystal Structure and Non-Hydrostatic Stress-Induced Phase Transition of Urotropine Under High Pressure.

High-pressure behavior of hexamethylenetetramine (urotropine) was studied in situ using angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) and Fourier-transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure-transmitting media to study the effect of deviatoric stress on phase transformations. Up to 4 GPa significant damping of molecular librations and atomic thermal motion was observed. A first-order phase transition to a tetragonal structure was observed with an onset at approximately 12.5 GPa and characterized by sluggish kinetics and considerable hysteresis upon decompression. However, it occurs only in non-hydrostatic conditions, induced by deviatoric or uniaxial stress in the sample. This behavior finds analogies in similar cubic crystals built of highly symmetric cage-like molecules and may be considered a common feature of such systems. DFT computations were performed to model urotropine equation of state and pressure dependence of vibrational modes. The first successful Hirshfeld atom refinements carried out for high-pressure diffraction data are reported. The refinements yielded more realistic C-H bond lengths than the independent atom model even though the high-pressure diffraction data are incomplete.

Effect of cationic substitution on the pressure-induced phase transitions in calcium carbonate

Abstract The high-pressure CaCO3 phase diagram has been the most extensively studied within the carbonates group. However, both the diverse mineralogy of carbonates and the abundance of solid solutions in natural samples require the investigation of multi-component systems at high pressures (P) and temperatures (T). Here we studied a member of the CaCO3–SrCO3 solid-solution series and revealed the effect of cationic substitution on the pressure-induced phase transitions in calcium carbonate. A synthetic solid solution Ca0.82Sr0.18CO3 was studied in situ by Raman spectroscopy in a diamond-anvil cell (DAC) up to 55 GPa and 800 K. The results of this work show significant differences in the high-pressure structural and vibrational behavior of the (Ca,Sr)CO3 solid solution compared to that of pure CaCO3. The monoclinic CaCO3-II-type structure (Sr-calcite-II) was observed already at ambient conditions instead of the “expected” rhombohedral calcite. The stress-induced phase transition to a new high-pressure modification, termed here as Sr-calcite-IIIc, was detected at 7 GPa. Sr-calcite-VII formed already at 16 GPa and room T, which is 14 GPa lower compared to CaCO3-VII. Finally, crystallization of Sr-aragonite was detected at 540 K and 9 GPa, at 200 K lower T than pure aragonite. Our results indicate that substitution of Ca2+ by bigger cations, such as Sr2+, in CaCO3 structures can stabilize phases with larger cation coordination sites (e.g., aragonite, CaCO3-VII, and post-aragonite) at lower P-T conditions compared to pure CaCO3. The present study shows that the role of cationic composition in the phase behavior of carbonates at high pressures should be carefully considered when modeling the deep carbon cycle and mantle processes involving carbonates, such as metasomatism, deep mantle melting, and diamond formation.

Study of the mechanical properties and toughening mechanism of ZrO2 particles toughened Si3N4 ceramics

Si3N4 ceramic has excellent properties such as high temperature resistance, high hardness, and high thermal stability, but it has the disadvantages of high hardness and brittleness and difficulty in later processing. In this paper, ZrO2 was used as toughening phase, and ZrO2 toughened Si3N4 ceramics was prepared by injection molding. The effects of ZrO2 sintering temperature and content on the mechanical properties and fracture morphology were studied. Experiments show that when the ZrO2 content is 10 wt.% and the sintering temperature reaches 1650 °C, the bending strength and fracture toughness of Si3N4 ceramics reach the maximum at the same time, which are 767 MPa and 8.7 MPa·m1/2, respectively. The density is high. XRD analysis revealed that if the sintering temperature is too high, the ZrO2/Si3N4 system will generate a large number of ZrN impurity phases that cannot be phase-transformed, which ultimately affects the ceramic properties. According to fracture morphology, the toughening mechanism of ZrO2 is stress-induced phase transition.

Analytical study on phase transition of shape memory alloy wire under uniaxial tension

This paper considers the stress-induced phase transitions of shape memory alloy slender cylinder, and analytically studies the phase transition process and the associated instability. A three-dimensional (3D) phenomenological model with an internal variable is adopted, which is simplified to a 1D system of two strains in three regions (austenite, martensite and phase transition regions). Suitable boundary conditions and interface conditions are proposed. Theoretically, it is a free boundary problem, as the position and shape of phase interfaces are unknown. We then focus on planar interfaces (which are energetically favored), and a symmetric case when phase transition occurs in the middle. For given applied stress, two-region solutions, three-region solutions and the connecting solutions between them are obtained analytically or semi-analytically, including many period-k solutions. Two-region solutions show that phase transition does not take place at one point, but simultaneously in a small region. The width of phase transition region is found analytically, revealing the roles of the material and geometrical parameters. Three-region solutions represent localized inhomogeneous deformations in experiments, and capture that the stress stays almost at the Maxwell stress during propagation of transformation front. For displacement-controlled process, the transition process is demonstrated by the stress-strain curve, which captures the stress drop/rise and the transition from homogeneous deformations to period-1 localized inhomogeneous deformations. When the radius is smaller than a critical value (given by material constants), the stress drop is very sharp due to transition of solutions in a snap-back bifurcation. These features show good agreement with experimental observations and shed light on the difficulties of numerical simulations.

A crystal plasticity based constitutive model accounting for R phase and two-step phase transition of polycrystalline NiTi shape memory alloys

Experimental observations show that the phase transition (PT) between austenite (A) and martensite (M) phases in NiTi shape memory alloys (SMAs) often occurs as a two-step process involving an intermediate phase, i.e., rhombohedral (R) phase (Helbert et al., 2014). In this work, a constitutive model is constructed to predict the phase transitions (PTs) among three phases (i.e., A, R and M ones) based on crystal plasticity theory. At single crystal scale, austenite, 4 variants in R phase and 24 variants in martensite one are introduced through certain relationships of crystallographic orientation. The constitutive model is developed in the framework of irreversible thermodynamics with considering various inelastic deformation mechanisms, i.e., the PT between austenite and R phases, the one between mixed A+R and martensite phases, and the reorientation/detwinning of R phase. At polycrystalline scale, to estimate the interactions among grains and obtain the overall response of polycrystalline aggregates, the developed single crystal constitutive model is linearized and implemented into an incremental self-consistent homogenization scheme. The capability of the newly developed constitutive model to describe the stress-induced PTs among three phases of polycrystalline NiTi SMAs is validated by comparing the predictions with the experimental data over a wide range of temperature. Furthermore, the effect of texture on the asymmetric tension-compression response of NiTi SMAs undergoing two-step PT is discussed.

Grain size-dependent energy partition in phase transition of NiTi shape memory alloys studied by molecular dynamics simulation

Nanocrystalline NiTi shape memory alloys show fundamental changes in phase transition behavior when the grain size is reduced down to nano-scale (grain size <30 nm). However, due to the extreme difficulties of in-situ experimental observation, universally acknowledged physical mechanisms and detailed microstructures at atomic level are still not clear. In this paper, detailed microstructure images and quantified energy partition at atomic level during stress-induced phase transition are obtained by molecular dynamics simulation. Phase transition is gradually suppressed and incomplete phase transition occurs as grain size decreases. The potential energy landscape of the nanocrystalline system changes significantly from nonconvex to convex, which leads to corresponding changes in stress–strain response and microstructural evolution. With decreasing grain size, the interface (grain boundary and phase boundary) energy makes much more contributions in variation of the system potential energy than the crystallite (austenite and martensite) energy. The mechanism of energy dissipation changes from atomic interface friction in phase transition to plastic deformation caused by grain boundary sliding. It is the gradual dominance of interfacial energy terms in total potential energy that leads to the observed fundamental changes of phase transition behavior in nanocrystalline NiTi.

Stress-induced structural phase transition of 3C–SiC with TLK structure in a nano-abrading process

TLK (Terrace-Ledge-Kink) structure such as surface steps is often found on the surface of SiC materials. Removal behavior of SiC substrates with TLK structure has not been studied in a fixed abrasive polishing under nano-abrasion conditions. In this paper, the effect of TLK structure on the abrasion temperature, stress, and structural transition of SiC substrates during the nano-abrading process is pursued by molecular dynamics (MD) simulation. The results show that the average stress and temperature decrease with the increase of ledge numbers in the TLK structure. It is found that crystalline-to-amorphous (C–A) phase transition occurs. The high-density amorphorization of SiC is induced by a high shear stress, which transforms to low-density amorphous SiC with the release of shear stress. Furthermore, unlike previous reports, the pressure-induced 6-fold coordinated structure in 3C–SiC in this study, however, does not possess a high-pressured phase transition (HPPT) to rocksalt structure; instead, a disordered structure is found. The ductile domain removal goes through two stages: first through the dislocation nucleation and propagation at the initial abrading stage and is then followed by the plastic flow of the amorphous atoms after sliding over the ledge. The presence of TLK structures benefits the plastic deformation of the SiC substrate.

A new mechanoluminescence phosphor Na3Sc2(PO4)3:Eu2+: Phase transition-assisted defect formation in a polymorphic composition

A new mechanoluminescent phosphor was developed from a sodium (Na) superionic conductor (NASICON)-structured Na3Sc2(PO4)3:Eu2+ phosphor that is known for its self-healing properties. The compound that crystalized assuming monoclinic C2/c symmetry was found to be blue-emitting, with no noticeable persistent luminescence. Thermoluminescence analysis showed that the phosphor had two prominent distinct thermal emission bands corresponding to the high-temperature β- and γ-phases of the composition. The mechanoluminescence properties of the material that does not have any persistent luminescence at room temperature were investigated by imparting impulsive strain. The compound on charging with 365 nm radiation was found to have significant mechanoluminescent emission originating from shallow defects present in the β-phase of composition that formed by the stress-induced phase transition process. Its emission characteristics and temporal behavior were investigated by varying the impact velocity.

Deviatoric stress-induced quasi-reconstructive phase transition in ZnTe

A new phase transition mechanism induced by deviatoric stress was found and named as “quasi-reconstructive” transition.