Thermally-induced Phase Transformation Research Articles

Synergistic Engineering of Energy Band Alignment and Interfacial Electric Field Distribution over Bi-bismuth-Based Hetero-nanofibers for Boosting Visible-Light-Driven Photocatalytic Ammonia Synthesis and Antibiotic Removal.

Synergistic engineering of energy band alignment and interfacial electric field distribution is essential for photocatalyst design but is still challenging because of the limitation on refined regulation in the nanoscale. This study addresses the issue by employing surface modification and thermal-induced phase transformation in Bi2MoO6/BixOyIz hetero-nanofiber frameworks. The energy band alignment switches from a type-II interface to a Z-scheme contact with stronger redox potentials and inhibited electron traps, and the optimized built-in electric field distribution could be reached based on experimental and theoretical investigations. The engineered hetero-nanofibers exhibit outstanding visible-light-driven photocatalytic nitrogen reduction activity (605 μmol/g/h) and tetracycline hydrochloride removal rate (81.5% within 30 min), ranking them among the top-performing bismuth series materials. Furthermore, the photocatalysts show promise in activating advanced oxidants for efficient organic pollutant degradation. Moreover, the Bi2MoO6/Bi5O7I hetero-nanofibers possess good recycling stability owing to their three-dimensional network structure. This research offers valuable insights into heterojunction design for environmental remediation and industrial applications.

Temperature-dependent synchrotron XRD study and electrical properties of the (1-x)BZT-(x)BCT lead-free piezoceramics

In recent years, researchers have shown the feasibility of the BZT-xBCT lead-free piezoelectric ceramics for using in various applications such as actuator, energy harvester, high-frequency ultrasonic transducer, etc. However, little evidence of temperature-dependent electrical properties of the BZT-xBCT ceramic was found. Moreover, some researchers have utilized Raman spectroscopy to observe the phase transition of the BZT-xBCT ceramic, but the Raman spectra of ferroelectric polymorphic phases are almost identical and hard to distinguish. In contrast, synchrotron radiation exhibits a high degree of monochromatization and collimation with smaller wavelength than x-ray tubes, resulting in the improvement of resolution for identifying the overlapping peaks. Therefore, this work aims to determine phase coexistence of the BZT-xBCT ceramic near phase boundary region by using high-resolution synchrotron x-ray powder diffraction in comparison with the temperature-dependent electrical properties. This work found that the occurrence of thermally-induced polymorphic phase transformations for the BZT-xBCT ceramics plays a significant role in the observed temperature-dependent electrical properties. Moreover, this work observed a trace of surface damaged layer (the presence of low-angle shoulder in the synchrotron XRD profiles) from mechanical grinding during sample preparation for XRD measurement, which has not previously been found in the BZT-xBCT ceramics. These finding will help to better understand the temperature-dependent functional properties of the BZT-xBCT ceramic for transferring into practical applications.

FeAu mixing for high-temperature control of light scattering at the nanometer scale.

Control of the optical properties of a nanoparticle (NP) through its structural changes underlies optical data processing, dynamic coloring, and smart sensing at the nanometer scale. Here, we report on the concept of controlling the light scattering by a NP through mixing of weakly miscible chemical elements (Fe and Au), supporting a thermal-induced phase transformation. The transformation corresponds to the transition from a homogeneous metastable solid solution phase of the (Fe,Au) NP towards an equilibrium biphasic Janus-type NP. We demonstrate that the phase transformation is thermally activated by laser heating up to a threshold of 800 °C (for NPs with a size of hundreds of nm), leading to the associated changes in the light scattering and color of the NP. The results thereby pave the way for the implementation of optical sensors triggered by a high temperature at the nanometer scale via NPs based on metal alloys.

Thermal/Water-Induced Phase Transformation and Photoluminescence of Hybrid Manganese(II)-Based Chloride Single Crystals.

Mn(II)-based hybrid halides have attracted great attention from the optoelectronic fields due to their nontoxicity, special luminescent properties, and structural diversity. Here, two novel organic-inorganic hybrid Mn(II)-based halide single crystals (1-mpip)MnCl4·3H2O and (1-mpip)2MnCl6 (1-mpip = 1-methylpiperazinium, C5H14N2+) were grown by a slow evaporation method in ambient atmosphere. Interestingly, (1-mpip)2MnCl6 single crystals exhibit the green emission with a PL peak at 522 nm and photoluminescence quantum yields (PLQYs) of ≈5.4%, whereas (1-mpip)MnCl4·3H2O single crystals exhibit no emission characteristics. More importantly, there exists a thermal-induced phase transformation from (1-mpip)MnCl4·3H2O to emissive (1-mpip)2MnCl6 at 372 K. Moreover, a reversible luminescent conversion between (1-mpip)MnCl4·3H2O and (1-mpip)2MnCl6 was simply achieved when heated to 383 K and placed in a humid environment or sprayed with water. This work not only deepens the understanding of the thermal-induced phase transformation and humidity-sensitive luminescent conversion of hybrid Mn(II)-based halides, but also provides a guidance for thermal and humidity sensing and anticounterfeiting applications of these hybrid materials.

In-situ STEM study on thermally induced phase transformation of magnetic (Nd0.75Ce0.25)2Fe14B ribbons

Studying the phase transformation and microstructure evolution of magnetic Nd-Ce-Fe-B nanocrystalline melt-spun ribbon is of paramount significance in developing this important class of magnetic materials. In this work, the thermal-induced phase transformation of (Nd0.75Ce0.25)2Fe14B nanocrystalline sample was revealed via in-situ heating scanning transmission electron microscopy (STEM) experiment (RT-750 ℃). Starting from a single-phase (Nd0.75Ce0.25)2Fe14B nanocrystalline matrix at room temperature (RT), grain boundary (GB) diffusion behavior was investigated at an atomic scale. Our result shows that the rare earth elements accumulate at GB area from 200 °C and form a uniform thin amorphous layer between grains. The decomposition of the primary phase was observed at about 350 ℃ and crystalized as BCC-Fe, Fe2B, and (Nd0.75Ce0.25)2O3 phases driven by thermal activation at a higher temperature. This work provides the essential information of phase transformation and microstructure evolution of NdCeFeB-based magnets at high temperatures and new insights into thermal treatment designing and thermal stability considerations.

Use of duplex microstructures in steel for estimation of plastic deformation in high-speed machining chips

Abstract It is shown that chip formation in high-speed milling of a steel remains unaffected by the presence of a volume fraction of about 10 % ferrite to either martensitic or pearlitic microstructures. Ferrite grains remain visible within the chips and can, therefore, be used for an estimation of the local plastic deformation. In case of the martensite structure, a deformation of 3000 % was measured in the white etching secondary shear zone, while a considerable amount of deformation even takes place within chip segments. The presence of ferrite grains within the white layer is an indication of a thermally-induced phase transformation occurring within the secondary shear zone of the chips.

A phenomenological model for thermally-induced hysteresis in polycrystalline shape memory alloys with internal loops

In the current study, a 1-D phenomenological model is constructed to capture the temperature-induced hysteretic response in polycrystalline shape memory alloys (SMAs). The martensitic and austenitic transformations are regarded as the first-order transitions. A differential single-crystal model is formulated on the basis of Landau theory. It is assumed that the transformation temperatures follow the normal distribution among the grains due to the anisotropic stress field developed in the material. The polycrystalline hysteretic response is expressed as the integration of single-crystal responses. Besides, the prediction strategy for incomplete transitions is presented, and the first-order reversal curves are obtained via density reassignment. The proposed model is numerically implemented for validation. Comparisons between the modeling results and the experimental ones demonstrate the capability of the proposed model in addressing the hysteresis in thermally-induced phase transformations.

Thermally-induced α→β phase transformation interweaving with abnormal α grain growth in hot extruded TNM alloy

The microstructural and crystallographic features of the β phase in TNM alloy during the hot extrusion at 1290 °C and the subsequent cooling process were investigated. Except the original grain boundary β phase, two categories of β particles, along grain boundaries of primarily recrystallized α grains (intergranular β) and in grain interiors of abnormally grown α grains (intragranular β), were found in the extruded microstructure. The former obeyed the Burgers orientation relationship with, at least, one of the neighboring α grains, whereas the latter did not show any specific orientation relationship with the α host. Analysis revealed that the thermally-induced α→β phase transformation interweaving with the abnormal α grain growth happened during the transition period from end-extrusion to water-quenching. The intergranular β particles were derived from the thermally-induced α→β phase transformation, and the intragranular β particles were resulted from the intergranular β precipitates after being swallowed by the abnormally grown α grains. The present work provides new information of thermally-induced phase transformation by adiabatic heating and the annexation of the second phase by abnormal grain growth during high-speed hot deformation.

Effect of Low-Temperature Aging on Thermally-Induced Phase Transformation of NiTi Wire with a Wide Range of Grain Sizes

Thermally-induced phase transformation (PT) is of significance and value to the application of NiTi alloy components. Low-temperature aging (LTA) treatment was used to alter PT characteristics of NiTi alloys avoiding undesirable grain growth. Effect of LTA on PT of NiTi wires with a wide range of grain sizes from 34 nm to 8021 nm was investigated in this study. As the average grain size varies from 34 to 217 nm, the temperature of the B2↔R transformation increase as a result of LTA, and the increasing effect is more obvious at a larger grain size. For NiTi alloys with average grain sizes ranging from 523 to 1106 nm, transformation sequence changes from B2↔B19' to B2↔R due to LTA. For the sample with an average grain size of 2190 nm, the B2↔B19' transformation is replaced by B2↔R←B19' after LTA. When the average grain size is larger than 2190 nm, transformation sequence changes from B2↔B19' to B2↔R↔B19' after LTA. Transmission emission microscope observations reveal that the above-mentioned PT behavior correlates with the coupled effect of grain size and precipitation. The precipitation of Ni4Ti3 in the grains with a size smaller than ~150 nm is inhibited after LTA, the temperature of B2→R of samples with average GS smaller than ~150 nm still is elevated due to the inhomogeneous grain size of NiTi wires.

SMALLBug: A 30-mg Crawling Robot Driven by a High-Frequency Flexible SMA Microactuator

We present the design, fabrication and experimental testing of SMALLBug, a 30-mg crawling microrobot that is 13 mm in length and can locomote at actuation frequencies of up to 20 Hz. The robot is driven by an electrically-powered 6-mg bending actuator that is composed of a thin shape-memory alloy (SMA) wire and a carbon-fiber piece that acts as a loading leaf-spring. This configuration enables the generation of high-speed thermally-induced phase transformations of the SMA material to produce high-frequency periodic actuation. During development, several actuator prototypes with different mechanical stiffnesses were tested and characterized by measuring their bending motions when excited with pulse-width modulation (PWM) voltages with a variety of frequencies and duty cycles (DCs). In a similar manner, the displacement-force characteristic of the actuator chosen to drive SMALLBug was identified by measuring its bending displacements under a number of different loads ranging from 4.22 to 83.8 mN. The locomotion capabilities of SMALLBug were experimentally tested at three different input actuation frequencies, which were observed to produce three distinct gaits. At the low frequency of 2 Hz, the robot locomotes with a crawling gait similar to that of inchworms; at the moderate frequency of 10 Hz, the robot advances smoothly at an approximately constant speed using a shuffling gait; and at the high frequency of 20 Hz, the robot generates small and fast jumps in a galloping gait, reaching average speeds of up to 17 $\boldsymbol{\text {mm}} \cdot \boldsymbol{\text {s}}^{\boldsymbol{\text {--}}\boldsymbol{\text {1}}}$, equivalent to 1.3 body-lengths per second (BLPS).

Thermal effect on oxidation layer evolution and phase transformation in grinding of Fe-Ni super alloy

This article is devoted to investigate thermal damage and its influences on phase transformation and surface characteristics in grinding of Fe-Ni super alloy. From the oxidation analysis, it was found that higher thermal effect could cause a worse subsurface damage layer and higher Oxygen proportion. In terms of the phase transformation, the results show that the volume fractions of martensite and austenite increase while that of ferrite decreases with elevated grinding temperature, which lead to an increment of surface hardness. Based on these analyses, the thermal induced phase transformation can be reduced by increasing work speed and decreasing depth of cut.

Thermally-induced phase transformations in KNNS-BNKZ lead-free piezoceramics

Promising piezoelectric properties have been reported in potassium sodium niobate-based ceramics by introducing Bi0.5(Na0.82K0.18)0.5ZrO3 (BNKZ) into K0.48Na0.52Nb0.95Sb0.05O3 (KNNS) solid solutions in order to control the polymorphic phase transformation temperatures. In the present study, synchrotron x-ray powder diffraction (SXPD) was employed in combination with dielectric and ferroelectric measurements in order to clarify the influence of BNKZ on the phase transition temperatures of (1-x)KNNS-(x)BNKZ ceramics (with x = 0 to 0.05). The results, presented in terms of temperature-dependent SXPD patterns, dielectric permittivity and thermal depolarisation characteristics, confirmed that polymorphic phase transformation temperatures all shifted in a systematic manner with increasing BNKZ content. Broadening of the phase transition regions was also observed with increasing BNKZ content, leading to improvements in thermal stability of the ferroelectric properties. Microstructural examination of the KNNS-BNKZ ceramics revealed the presence of core-shell microstructures; this was correlated with the presence of weak shoulders on the diffraction peaks.

Thermal and Mechanical Stability of Austenite in Metastable Austenitic Stainless Steel

The roles of grain size, texture, strain, and strain rate on the thermal and mechanical stability of austenite in AISI 321 metastable austenitic stainless steel were studied. Ultrafine grain (UFG), fine grain (FG), and coarse grain (CG) specimens with average grain sizes of 0.24, 3, and 37 µm sizes, respectively, were investigated. To determine the thermal stability of austenite (TSA), samples were soaked in liquid nitrogen (− 196 °C) for varying times between 0.5 and 24 hours. On the other hand, the mechanical stability of austenite (MSA) was studied by subjecting cylindrical specimens to both quasi-static (4.4 × 10−3 s−1) and dynamic loading conditions (between 1300 and 8800 s−1). Thermally-induced α′-martensite was only observed at an incumbent time in AISI 321 to suggests an isothermal martensitic transformation occurred. Both Kurdjumov-Sachs ($$ \{ 111\}_{\gamma } ||\{ 110\}_{{\alpha^{\prime}}} $$ and $$ \langle \bar{1}01\rangle_{\gamma } ||\langle 1\bar{1}1\rangle_{{\alpha^{\prime } }} $$) and Nishiyama–Wasserman ($$ \{ 111\}_{\gamma } ||\{ 110\}_{{\alpha^{\prime}}} $$ and $$ \langle 112\rangle_{\gamma } ||\langle 011\rangle_{{\alpha^{\prime } }} $$) orientation relationships existed between the untransformed γ and thin-plate α′-martensite. The thermally-induced phase transformation was highly suppressed in UFG specimens. While TSA decreased with an increase in grain size, MSA decreased with a decrease in grain size. While thin-plate α′ predominantly formed in the thermally-treated AISI 321 steel (FG and CG specimens only), lath and irregularly-shaped α′ formed in the specimens deformed under quasi-static and dynamic loading conditions, respectively. Irrespective of strain rate, deformation-induced α′ in UFG specimens inherited the morphology of the deformed austenite grain that is equiaxed. Irrespective of grain size, MSA also decreased with increase in strain (up to a critical strain for specimens deformed under dynamic loading condition) and decrease in strain rate. In the event of adiabatic shear band (ASB) formation in a specimen deformed at high strain rate, MSA increased as the ASB was approached due to the temperature rise in the ASB region. Electron backscattered diffractometry examination revealed that the evolution of both thermally- and deformation-induced martensite is orientation-dependent in FG and CG specimens. The instability (thermal and mechanical) of the austenite phase is highest in the RD/CD||[100]-oriented grains (RD and CD are rolling and compression directions, respectively), followed by grains oriented near RD/CD||[110] and RD/CD||[111], in that order. These findings could open a new window of engineering the initial texture of metastable austenitic stainless steel to either aid thermally and/or mechanically-stable austenite phase or promote both isothermal and deformation-induced martensitic phase transformation.

Stress-induced CsPbBr3 nanocrystallization on glass surface: Unexpected mechanoluminescence and applications

In this work, we discovered an unexpected mechanoluminescence (ML) phenomena occurring when transforming amorphous into crystalline, due to the stress-induced precipitation of CsPbBr3 perovskite nanocrystals on glass surface. It is revealed that, unlike the conventional thermal-induced phase transformation mechanism, the breakage of bonding of glass network provides the energy for nucleation and growth, and the shear stress avoids the long-range migration of structural units for crystallization. Such unique ML phenomenon enables the visualization of dynamical force that is inaccessible by common strategy, and so, opens up some novel applications, such as the pressuresensitive “glassy pencil” to learn people’s writing habits, and the Pb2+-detection with good sensitivity and selectivity. These findings not only demonstrate an effective route for the preparation of perovskite materials in a green, time-saving, low cost, and scalable way, enrich the knowledge of glass crystallization mechanism, but also exploit a useful avenue to quantitatively visualize the dynamical force.

Thermal-Induced Phase Transformation Behavior of NiTiNb Hypoeutectic, Eutectic, and Hypereutectic Alloys

In the present work, three NiTiNb alloys with nominal compositions of Ni50–x/2Ti50–x/2Nbx (x = 18, 20 and 22, at.%) were prepared. The microstructure, thermal-induced phase transformation, and phase components of NiTiNb hypoeutectic, eutectic, and hypereutectic alloys were investigated by scanning electron microscopy coupled with energy dispersive spectrometer (SEM/EDS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD), respectively. Two peaks occurred in the DSC curves of Ni41Ti41Nb18 solution at 750 and 850 °C. The different microstructures of NiTiNb hypoeutectic, eutectic and hypereutectic alloys, the occurrence of two peaks in the DSC curves, and the characteristic of martensite transformation temperature were analyzed and discussed. The results show that different Nb content leads to different microstructures of Ni50–x/2Ti50–x/2-Nbx alloys. Moreover, the difference of Ni/Ti ratio between the primary NiTi matrix and NiTi in eutectic structure strongly influenced the phase transformation behavior that the DSC curves of Ni41Ti41Nb18 alloy show two peaks. Furthermore, under the same solution treatment, the Ni40Ti40Nb20 alloy has a lower Ms than the other two alloys. The Ms has a tendency to decrease with an increase in solution temperature.

The Analysis of Thermal-Induced Phase Transformation and Microstructural Evolution in Ni-Ti Based Shape Memory Alloys By Molecular Dynamics

Shape memory alloys has been widely applied on actuators and medical devices. The transformation temperature and microstructural evolution play two crucial factors and dominate the behavior of shape memory alloys. In order to understand the influence of the composition of the Ni-Ti alloys on the two factors, molecular dynamics was adopted to simulate the temperature-induced phase transformation. The results were post-processed by the martensite variant identification method. The method allows to reveal the detailed microstructural evolution of variants/phases in each case of the composition of Ni-Ti. Many features were found and having good agreement with those reported in the literature, such as the well-known Rank-2 herringbone structures; the X-interface; Ni-rich alloys have lower transformation temperature than Ti-rich alloys. In addition, some new features were also discovered. For example, the Ti-rich alloys enabled an easier martensitic transformation; the nucleated martensite pattern determined the microstructural evolution path, which also changed the atomic volume and temperature curves. The results generated in the current study are expected to provide the design guidelines for the applications of shape memory alloys.

Real-time observation of the thermally-induced phase transformation in GeTe and its thermal expansion properties

The GeTe-based system has long been considered as a promising candidate system for various functional applications; many of which are directly related to the polymorphic phase transformation in their crystalline forms. Consequently, the microstructure underlying their intriguing phase transition has been the subject of numerous studies. Here we provide real-time observation of the microstructural changes associated with the reversible pseudo-cubic (or rhombohedral) to cubic GeTe phase transition using high-voltage transmission electron microscopy (HV-TEM) operating at 1,250 kV and complementary high-temperature X-ray diffraction (XRD). As a result of the phase transition, the pseudo-cubic GeTe domain's configuration significantly changes from its original band-like to a spike-like morphology with a different orientation after a heating/cooling cycle. The coefficients of thermal expansion (CTE) properties as a function of temperature are also explored in relation to the GeTe phase transition.

Hybrid structure of white layer in high carbon steel \u2013 Formation mechanism and its properties

This study identifies for the first time, the hybrid structure of the white layer in high carbon steel and describes its formation mechanism and properties. The so-called ‘white layer’ in steel forms during high strain rate deformation and appears featureless under optical microscopy. While many researchers have investigated the formation of the white layer, there has been no definitive study, nor is there sufficient evidence to fully explain the formation, structure and properties of the layer. In this study, the formation, morphology and mechanical properties of the white layer was determined following impact testing, using a combination of optical and SE- microscopy, HR-EBSD, TKD and TEM as well as nano-indentation hardness measurements and FE modelling. The phase transformation and recrystallization within and near the white layer was also investigated. The microstructure of the steel in the white layer consisted of nano-sized grains of martensite. A very thin layer of austenite with nano sized grains was identified within the white layer by HR-EBSD techniques, the presence of which is attributed to a thermally-induced reverse phase transformation. Overall, the combination of phase transformations, strain hardening and grain refinement led to a hybrid structure and an increase in hardness of the white layer.

Nonradiation Cellular Thermometry Based on Interfacial Thermally Induced Phase Transformation in Polymer Coating of Optical Microfiber.

A nonradiation approach based on thermoresponsive polymer coated silica microfibers has been developed. A highly thermoresponsive and biocompatible poly(N-isopropylacrylamide) (pNIPAM) was surface functionlized to conjugate to the tapered silica microfiber with waist diameter of 7.5 μm. The interfacial phase transtition of coating triggered by the lower critical solution temperature (LCST) causes a drastic molecular morphological change in the body temperature range of 35-42 °C. This surface morphological change strongly modulates optical path difference between the higher order and the fundamental mode propagating in the microfiber because of the evanescent-field interaction and, therefore, shifts the intermodal interference fringe. Owing to the nonradiation-based nature, the thermoresponsive polymer coated microfiber enables an improved thermal sensitivity of 18.74 nm/°C and, hence, a high-temperature resolution of millidegree. Furthermore, the micrometer-sized footprint enables its easy implantation in human organs for cellular thermometry and for the potential of in vivo applications.

Plastic Deformation and Thermal Induced Phase Transformation in 2507 Type Super Duplex Stainless Steel

The aim of this study was to investigate the effect of the previously applied cold rolling and the latter heat treatment for the eutectoidal decomposition of δ-ferrite in 2507 type superduplex stainless steel (SDSS). The samples were cold rolled at seven different deformation rates which was followed by heat treatment at were 20, 700, 750, 800 and 850 °C temperatures. The rolled and heat treated samples were investigated by hardness tester, AC magnetometer and thermoelectric power measurement. The activation energy of the decomposition was determined by the Arrhenius equation through the results of the AC magnetometer measurement.