Phase Transformation Characteristics Research Articles

Crystallographic Features of Phase Transformations in High-Strength Low-Carbon Pipe Steel

Crystallographic Features of Phase Transformations in High-Strength Low-Carbon Pipe Steel

Numerical and Experimental Study of a Wearable Exo-Glove for Telerehabilitation Application Using Shape Memory Alloy Actuators

Hand paralysis, caused by conditions such as spinal cord injuries, strokes, and arthritis, significantly hinders daily activities. Wearable exo-gloves and telerehabilitation offer effective hand training solutions to aid the recovery process. This study presents the development of lightweight wearable exo-gloves designed for finger telerehabilitation. The prototype uses NiTi shape memory alloy (SMA) actuators to control five fingers. Specialized end effectors target the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints, mimicking human finger tendon actions. A variable structure controller, managed through a web-based Human–Machine Interface (HMI), allows remote adjustments. Thermal behavior, dynamics, and overall performance were modeled in MATLAB Simulink, with experimental validation confirming the model’s efficacy. The phase transformation characteristics of NiTi shape memory wire were studied using the Souza–Auricchio model within COMSOL Multiphysics 6.2 software. Comparing the simulation to trial data showed an average error of 2.76°. The range of motion for the MCP, PIP, and DIP joints was 21°, 65°, and 60.3°, respectively. Additionally, a minimum torque of 0.2 Nm at each finger joint was observed, which is sufficient to overcome resistance and meet the torque requirements. Results demonstrate that integrating SMA actuators with telerehabilitation addresses the need for compact and efficient wearable devices, potentially improving patient outcomes through remote therapy.

Investigation of Phase Transformation and Fracture Pattern as a Result of Long-Term Chewing Simulation and Static Loading of Reduced-Diameter Zirconia Implants.

While zirconia implants exhibit osseointegration comparable to that of titanium, concerns arise regarding low-temperature degradation and its potential impact on fracture strength. This study investigated the phase transformation and fracture characteristics of zirconia dental implants after aging through chewing simulation and subsequent static loading. The experimental setup involved 48 one-piece monobloc zirconia implants with diameters of 3.0 mm and 3.7 mm that had straight or angled abutments, with crown restorations, which were divided into six groups based on intraoral regions. The specimens underwent chewing simulation equal to five years of oral service, which was followed by static loading. Statistical analyses were performed for the data obtained from the tests. After dynamic and static loadings, the fractured samples were investigated by Raman spectroscopy to analyze the phase composition and micro-CT to evaluate fracture surfaces and volume changes. According to the results, narrow-diameter zirconia implants have low mechanical durability. The fracture levels, fracture patterns, total porosity, and implant fracture volume values varied according to the implant diameter and phase transformation grade. It was concluded that phase transformation initially guides the propagation of microcracks in zirconia implants, enhancing fracture toughness up to a specific threshold; however, beyond that point, it leads to destructive consequences.

An investigation on stabilisation and phase transformation characteristics of Cu-Al-Be shape-memory alloys quenched in different media

ABSTRACT The aim of the present investigation is to fabricate the ternary Cu87.59, Al11.99 and Be0.42 (wt.%) shape memory alloy (SMA), and to study the effect of quenching medium on the phases, phase transformation, stabilisation, and shape recovery ratio. SMA was fabricated, betatized at high temperature (β) and then quenched into different media and quench types. The quenched SMAs are examined for phases, microstructure, phase transformation temperatures, martensite stabilisation and shape recovery ratio. XRD results reveal that all the quenched alloys are of complete martensite of 18 R and 2 H variants. Meta quench oil quenched SMAs possess pure martensite, smaller grain size, lower transformation temperatures, and rapid recovery, whereas silicone oil exhibits larger grain size and delay in recovery and the mechanisms are discussed in detail in the discussion part. MQ oil quenched SMAs are suitable and recommended for rapid response/recovery actuator applications with enhanced properties.

Morphology evolution and mechanism of massive three-level hierarchically porous silver fabricated by vapor phase dealloying

In this study, the Gasar process and vapor phase dealloying (VPD) method were combined to fabricate a massive three-level hierarchical porous silver (MTHPS), which composed of interconnected micron-sized, submicron-sized, and nanoporous structures. The key aspect of this study lies in the preparation of a hypoeutectic Gasar Mg91.6Ag8.4 alloy with the regular micron-scale pore structure as the dealloying precursor, improving the size of the hierarchical porous metal. Under high vacuum conditions, by adjusting the dealloying time and temperature, MTHPS samples with various morphologies were obtained. After dealloying, the MTHPS exhibited Gasar pores (diameter 376 ± 86 μm), submicron pores (diameter 465 ± 125 nm), and a continuous ligament/channel structure (pore size less than 70 ± 40 nm). The coarsening index was 3.6258, and the activation energy was measured to be 0.95 eV, indicating that the formation and coarsening of the pores during VPD are attributed to surface diffusion. The calculated evaporated mass of the precursor alloy after dealloying was very close to the experimental value (±0.004 g), indicating that the evaporation of Mg occurred simultaneously in both solid and liquid phases during the VPD process. This study elucidates the phase transformation characteristics, structural control, and diffusion mechanisms of MTHPS prepared by VPD, providing valuable insights for further research and applications of MTHPS.

Low-loss Se-based phase-change materials for infrared photonics

The work presents the results of comprehensive studies of the optical and transport properties, phase transition heats, the X-Ray diffraction and Raman spectra of Ge2Sb2Se4Te1, Sb2Se3 and Bi2Se3 samples obtained by vacuum thermal deposition. We demonstrate a high contrast in the refractive index and extinction coefficient in the spectral range in wavelengths of 500–1800 nm and transmissivity and reflectivity spectra in the range in wavelengths of 500–3000 nm. The investigated materials show low optical losses and high figure of merit in much of the IR-spectrum. Changes in structural properties are analyzed by XRD and Raman methods. Features of phase transformations are described by thermogravimetry and differential scanning calorimetry.

Optimization design and interface characteristics research of high damping NiTi - Nickel-Aluminum Bronze functional gradient composite coating additively manufactured by high-speed laser-directed energy deposition

The near-equatomic NiTi shape memory alloy demonstrates exceptional damping performance due to its distinctive low-temperature self-cooperative martensitic internal friction. This study successfully fabricated NiTi-NAB (Nickel-Aluminium bronze shape memory alloy) functionally graded composite coatings with excellent metallurgical bonding between layers on Q235 steel substrates by designing an appropriate interlayer structure and employing the high-speed laser-directed energy deposition (LDED). Through comprehensive evaluation of the composite coating's performance and the numerical simulations of heat transfer within the molten pool, we elucidated the impact of process parameter levels on the microstructure and phase transformation characteristics of the NiTi alloy coating (NTC). The phase composition and phase interface characteristics of the NTC surface and bonding interface were analyzed using an electron probe microanalyzer and transmission electron microscopy, while dynamic thermomechanical analysis was employed to evaluate the damping performance of the NTC. The results indicate that an optimal parameter combination area still exists within the NTC-LDED process parameter window, even with equal laser energy density. Insufficient parameter levels can lead to an increase of micro-defects within the NTC, consequently causing a deterioration in both the cohesion and deformation resistance of the coating. Excessively high parameter levels can lead to significant element loss and residual stress, which in turn contributes to an increase in microcracks within the coating. A considerable quantity of reaction product mixture phases was formed at the interface between NTC and NAB, tending to align coherently with the NAB phase interface. The NTC, prepared with optimal process parameters, exhibits exceptional damping performance with a damping ratio of 0.498 at internal friction equilibrium, rendering it highly promising for applications in surface erosion protection for fluid machinery.

Evaluation of hydrogen storage performance of Ti0.25Zr0.25V0.15Nb0.15Ta0.2 high-entropy alloy using calorimetric technique

The features of phase transformations during interaction of BCC-type Ti0.25Zr0.25V0.15Nb0.15Ta0.2 high-entropy alloy (HEA) with hydrogen and the accompanying thermal effects have been examined using the Tian-Calvet calorimetric technique. The alloy was produced by the pendent drop melt extraction method in the form of microfibers and then coated with a thin layer of palladium to eliminate the preliminary high-temperature activation and enable first hydrogenation at room temperature. Two reaction stages were distinguished on the measured heat emission curves. Using XRD data, these stages were attributed to the formation of a BCC-type hydrogen solid solution and a phase transition to FCC-type dihydride phase. Recorded values of the reaction enthalpy decrease in absolute terms from 145 kJ/mol H2 (dilute solid solution) to 73–77 kJ/mol H2 (BCC→FCC) and to 20 kJ/mol H2 (H solution in FCC dihydride). The overall heat emission of the entire process as a whole is 110 kJ/ mol H2. The course of the dehydrogenation process depends strongly on the applied temperature and at 493 K results in the formation of a BCT-type monohydride, which was not detected during hydrogenation. The detailed calorimetric data obtained here significantly change the previously existing ideas about thermal effects during this type HEAs hydrogenation, based on calculations using the Van't-Hoff equation. The reported findings are of special importance for various hydrogen related applications of HEAs

A regenerated cellulose fiber with high mechanical properties for temperature-adaptive thermal management

The escalating global population has led to a surge in waste textiles, posing a significant challenge in landfill management worldwide. In this work, ionic liquid 1-butyl-3-methylimidazole acetate ([Bmim]OAc) and DMF (N, n-dimethylformamide) were used as solvents to dissolve waste denim fabric, then vanadium dioxide (VO2) nanoparticles were introduced into the spinning solution, and cellulose fibers were regenerated by dry-wet spinning process, to promote the recycling of waste cotton fabric. Finally, regenerated cellulose fibers with high added value were prepared by dry-wet spinning. Through this innovative strategy, on the one hand, because VO2 can form a large number of hydrogen bonds between the regenerated cellulose molecules, and realize the cross-networking structure of the molecular chains inside the fiber, the mechanical properties of the regenerated cellulose fibers are enhanced. On the other hand, due to the thermal phase transformation characteristics of VO2, it also endows the regenerated cellulose fiber unique intelligent temperature control function. Compared with the pristine regenerated fiber, the tensile stress of the regenerated fiber after adding VO2 nanoparticles (F-VO2) increased by 25.6 %, reaching 158.68 MPa. In addition, the F-VO2 fibric provides excellent intelligent temperature control, reducing temperatures by up to 6.7 °C.

Effect of heat treatment conditions on the phase transformation characteristics of nitinol

Nitinol is the most widely used shape memory alloy in medical applications. In this study, the effect of different heat treatment conditions on the phase transformation characteristics of medical-grade nitinol was investigated. Nickel-rich nitinol wires containing 50.6% nickel with a diameter of 120 μm were used in the experimental studies. The nitinol wires were heat treated for 10 minutes at heat treatment temperatures between 540 and 570 °C. Then, nitinol wires were heat treated at a heat treatment temperature of 550 °C between 8 and 14 minutes. The austenitic and martensitic transition temperatures of these samples were measured using differential scanning calorimetry (DSC). In the experiments with 10 minutes of heat treatment time, transition temperatures decreased, and hysteresis increased with the increase in heat treatment temperature. This is related to the amount of precipitates in the structure. In the experiments carried out at 550 °C, transition temperatures decreased, and hysteresis increased with increasing heat treatment time. Experimental studies showed that the austenite finish (Af) temperature of all nitinol wire samples was below 37 °C, and they will exhibit superelasticity in the human body.

The mechanism for the superior isotropic mechanical properties attained in a cross rolling TiNb alloy

In the present study, the Ti–41Nb (wt.%) alloy featuring a microstructure composed of β and α″ phases have been prepared through the application of the Cross Rolling (CSR) technique to achieve a near-isotropic superior mechanical behavior. The experimental findings revealed that the CSR sample exhibits a uniform β matrix, randomly dispersed α″ martensite and a high density of dislocations and grain boundaries. Subsequent experiments unveiled that the CSR sample displays an almost isotropic mechanical response across three typical directions, Rolling Direction (RD), a 45° deviation from RD, and Transverse Direction (TD), evidenced by comparable stress-strain curve profiles and ultimate tensile strength (UTS) values. Due to the randomly distributed textures and high density of dislocations and grain boundaries, the stress-induced martensitic (SIM) transformation exhibits a similar characteristic in three typical directions, that is, the SIM transformation took place homogeneously and continuously. Consequently, the CSR sample can achieve a near-isotropic and outstanding mechanical performance due to the similar characteristics of martensitic phase transformation and the strengthening effect brought by the high density of dislocations and grain boundaries.

Study of titanium alloy Ti–Al–Zr–Nb–V during heating under deformation and its phase transformation features

An alloy based on Ti–Al–Zr–Nb–V was prepared and its deformation behavior at elevated temperatures was studied. The microstructure and phase of the alloys were characterized by optical microscopy, scanning electron microscopy, thermal analysis, and mechanical testing. The results showed that the Ti–Al–Zr–Nb–V alloy, when stretched, exhibits a superplasticity effect in the range of 975℃ to 1100℃, with an elongation of up to 400%. It was found that superplasticity develops in the temperature region of the α+β→β transition and is accompanied by a change in grain size and redistribution of alloying elements among phases.

Features of Phase Transformations in Porous Powder Materials

Features of Phase Transformations in Porous Powder Materials

Mechanical response and phase transformation characteristics of R-phase NiTi shape memory alloy under high strain rate compression

R-phase NiTi shape memory alloy (R-NiTi SMA) has many excellent properties, but there are application problems such as simple structure and high price. High velocity impact welding can effectively solve these problems, but the research on the mechanical response and phase transformation (PT) characteristics of R-NiTi SMA under dynamic deformation is lacking. Therefore, the quasi-static (0.001 s-1) and dynamic (500 s-1, 1000 s-1, 1500 s-1, 2000 s-1) compression experiments were conducted on R-NiTi SMA in this research. The results showed that the true stress-strain curves of R-NiTi SMA during deformation were characterized by three stages, including the superelastic, elastic, and plastic segments. The critical stress of austenite to R (A-R) and R to martensite (R-M) phase transformation increased with the increase of strain rate, and the phase transformation process gradually disappeared when the strain rate exceeded 1000 s-1, which was related to the velocities of A-R and R-M phase transformation. With the increase of strain rate, defects such as dislocations increased and hindered the phase transformation process during unloading, resulting in the increase of A-phase content. In addition, the enthalpy of the deformed samples decreased significantly and the temperature ranges of phase transformation increased slightly. This work deepens the understanding of the dynamic response of R-NiTi SMA and helps to expand the application of high strain rate processing technology in R-NiTi SMA.

Phase Transformation of Arsenic, Antimony and Lead in High-Grade Copper Matte Converting

The duration of the high-grade matte converting process is short, the amount of slag is small, and it is difficult for the original impurity removal operation in the low-grade matte converting process to meet the current production demand. Because the removal method for impurity elements during high-grade matte converting is unclear, the phase transformation of impurity elements during this process is investigated in this study. The results show that arsenic exists mainly in the form of FeAsO4 and As2O5, antimony in the form of Sb and Sb2O5, and lead in the form of PbS and PbO in high-grade matte. During the converting process, arsenic and antimony mainly exist in the melt in the form of oxides and gradually aggregate into large particles with increasing copper content in the melt. Lead exists in matte in the form of PbS until the end of the converting process, and PbS is not completely oxidized until the matte converted to blister copper phase. The phase transformation characteristics of copper, iron, sulfur and impurity elements in the process of high-grade matte converting were revealed. This study provides a theoretical reference for the formulation of an efficient impurity removal scheme for the converting process.

Studying the features of complex beryllium-containing silicate phases co-crystallization in zonal samples using the x-ray electron probe microanalysis method

Research subject. Silicate ingots containing four species-forming components Be, Mg, Al, and Si and belonging to the crystallization region of beryllium indialite (with the formula of Mg2BeAl2Si6O18 and a beryl-type structure). Aim. To investigate the fundamental problem of identifying the patterns of matter differentiation and the stable and metastable phase formation in silicate matrices. Methods. The evolution of the phase composition of silicate melts was registered using a temperature gradient method. Results. New data on the features of phase transformations in silicate melts belonging to the region of beryllium indialite were obtained by electron probe microanalysis (EPMA). Co-existing metastable and stable mineral phases were identified, and the similarity of their compositions with different structures was shown. The nature of impurity phases at each stage of crystallization was established. Conclusions. The evolutionary sequence of phase associations ensuring the crystallization of beryllium indialite and metastable phases of a similar composition, the nature of which is determined by the initial ratio of components, was experimentally recorded. The range of possible phase associations that co-crystallize or replace a stable phase with a beryl structure in melts from the region of existence of beryllium indialite in the BeO–MgO–Al2O3–SiO2 system was extended. The selectivity of the coloring element chromium entry into various phases of the studied system is shown depending on the capabilities of their structure. The addition of a chromophore is a reliable criterion for visualizing successive layers, zones, and areas of changing phase associations in the final ingot.

Trends in GeTe Thermoelectrics: From Fundamentals to Applications

AbstractGermanium telluride (GeTe) with ultrafast ferroelectric transition, Rashba‐like electronic transport, and anomalous phonon anharmonicity are historically studied for potential memorizing and thermoelectric applications. Due to recent breakthroughs in spintronics, valleytronics, orbitronics, pre‐eminent GeTe thermoelectrics have re‐attracted enormous interest from both academia and industries, with increasing reports of significant figure‐of‐merit over 2.7 and the maximum efficiency of up to 17.0%. Here, the emerging trends in advancing GeTe thermoelectrics, starting from fundamentals of phase transformation, crystal structure, bonding mechanisms, and transport characteristics, with a highlight on the roles of Ge_4s2 lone pairs, are timely overviewed. Technical insights in synthesis, characterization, property measurement, and computation are then summarized. After that, several innovative strategies for increasing the figure‐of‐merit, including entropy engineering, nanostructuring, and hybridization, which will further benefit near‐room‐temperature and n‐type performance, are examined. Moreover, high‐density and high‐efficiency devices with broad working temperatures are discussed as a result of rational configurational and interfacial design. In the end, perspective remarks on the challenges and outlook envisaging for next‐generation GeTe thermoelectrics, which will play a prominent role in future energy and environmental landscapes, are provided.

The driving characteristics of bidirectional SMA wire actuators - Theoretical modeling and experimental testing

Bidirectional shape memory alloy (SMA) wire actuators play a critical role in driving applications thanks to their characteristics in memory shaping and good overall performance. SMA wire actuators were often studied at a single load type, and there is no comprehensive comparison investigation of different SMA wire actuators in the literature. In this paper, the driving characteristics of four available types of SMA wire actuators, namely, dead-load, biased spring, differential type, and biased superelastic SMA wire actuators are modelled mathematically and then tested in laboratory settings. The characteristics of SMA wire actuators are quantitatively measured and then compared under a range of application scenarios. The output displacement and thermal-electric models of NiTi SMA wires are derived based on the Brinson constitutive model with stress effects in consideration. A customized SMA wire actuator test device is developed to evaluate the theocratical models and benchmark testing four types of SMA wires and their driving characteristics, including structure, design, displacement, response and recovery time, energy efficiency and hysteresis properties. The SMA wire phase transformation characteristics of the four actuators are tested under different activation currents, and then quantitatively compared. In conclusion, this paper adds theoretical and experimental significance to the literature on SMA wire actuators. The reference value on the phase transformation characteristics of SMA wires can be used to guide SMA application in industrial designs and enable theoretical studies in complementary research areas.

Influence of applied stress on shape memory characteristics of Ni50Ti45Cu5 (at.%) alloy subjected to thermomechanical cycling

Shape memory alloys have made rapid progress in many domains, primarily biomedical (endovascular stents, orthodontic archwires), and engineering (smart actuators, robotics, hydraulic couplings). The selection of a shape memory alloy for the indented application is based on its characteristic phase transformation temperatures. These characteristic temperatures are influenced by myriad parameters, such as composition, microstructure of the alloy, defect density, etc. When an shape memory alloy under an external load is subjected to cyclic operations to perform useful work, for example, actuators, these characteristic temperatures are modified. This study, therefore, aims to understand the influence of external loading on the shape memory characteristics of a Ni50Ti45Cu5 (at.%) alloy. A wire of 1.43 mm diameter and length of 100 mm was subjected to heating and cooling between its phase transformation temperatures in a cyclic manner under constant stress (of up to 60 MPa). The maximum recovery strain, actuation/retraction rate, and the stress influence coefficient were determined and compared with those of the other Ni-Ti and Cu-based shape memory alloys. The results show that raising the load level causes an increase in the transition temperatures, especially the Ms (martensite start temperature) rather than the other phase transformation temperatures (martensite finish (Mf), austenite start (As), austenite finish (Af)). It also significantly affects the recovery strain and the rate of retraction during forward transformation and the symmetry of operation.

Effect of Surface Roughness and Chemical Composition of Metastable Austenitic Stainless Steels on Electrochemical Polishing-Induced Martensitic Transformation

Herein, we analyzed the martensitic transformation kinetics during electrochemical polishing (EP) for stainless steel specimens with varying surface roughness and austenite stability. Martensite fraction measurement demonstrated that specimens with higher surface roughness and lower austenite stability exhibited relatively higher levels of martensitic transformation. To understand these phase transformation characteristics, the amount of charge build-up on the specimen surface during EP was calculated using COMSOL Multiphysics simulations for specimens with different surface roughness. The effect of charge build-up-induced stress was analyzed using previously published first-principles calculations. We found that specimens with higher surface roughness accumulated more charge build-up, resulting in greater stress and a martensitic transformation driving force. Furthermore, the critical energy required for the martensitic transformation was calculated using Thermo-Calc for specimens with different austenite stabilities. We demonstrated that the martensitic transformation kinetics during EP could be explained in terms of austenite stability, similar to the stress-induced martensitic transformation.Graphical