Phase Transformation Temperature Range Research Articles

Study on the phase transformation law of titanium micro alloyed non-oriented silicon steel

An experimental steel 50W600-Ti with 0.02C-0.09Ti (wt%) was designed based on 50W600. The CCT curves of the two experimental steels were determined using a thermal simulator, and the phase transformation laws of the two experimental steels under continuous cooling were investigated. The results show that the phase transformation temperature of 50W600 is between 926°C-1047°C, and the phase transformation temperature range decreases with the increase of cooling speed, while the phase transformation temperature of 50W600-Ti is between 838°C-1048°C, and the phase transformation temperature range varies less with the cooling speed; the matrix organization of the two experimental steels is ferrite, with a small amount of carburite at high cooling speed.

Development of High-Entropy Shape-Memory Alloys: A Review

High-entropy shape-memory alloys (HESMAs) exhibit unique properties, including high yield strength, a wide temperature range of phase transformation, and excellent thermal cycling stability, among others. Hence, they have broad prospects for research and application. Currently, various new high-entropy shape-memory alloys have been developed based on TiNi, Fe-based, Ti-based, and NiMn-based alloys. This article focuses on summarizing and analyzing the research status of various types of high-entropy shape-memory alloys, including their microstructure characteristics, martensitic phase transformation, and functional properties. The advantages and disadvantages of high-entropy shape-memory alloys compared to traditional shape-memory alloys are briefly discussed. Finally, based on the analysis of existing problems, future research prospects are proposed, hoping to provide assistance for the development and application of high-entropy shape-memory alloys in the future.

Mitigation of Thermal Instability for Electrical Properties in CaZrO3-Modified (Na, K, Li) NbO3 Lead-Free Piezoceramics.

Lead-free ceramics 0.96(Na0.52K0.48)0.95Li0.05NbO3-0.04CaZrO3 (NKLN-CZ) are prepared by using the solid-state procedure and two-step synthesis technique. The crystal structure and thermal stability of NKLN-CZ ceramics sintered at 1140-1180 °C are investigated. All the NKLN-CZ ceramics are ABO3-type perovskite phases without impure phases. With the increase in sintering temperature, a phase transition occurs in NKLN-CZ ceramics from the orthorhombic (O) phase to the concomitance of O-tetragonal (T) phases. Meanwhile, ceramics become dense because of the presence of liquid phases. In the vicinity of ambient temperature, an O-T phase boundary is obtained above 1160 °C, which triggers the improvement of electrical properties for the samples. The NKLN-CZ ceramics sintered at 1180 °C exhibit optimum electrical performances (d33 = 180 pC/N, kp = 0.31, dS/dE = 299 pm/V, εr = 920.03, tanδ = 0.0452, Pr = 18 μC/cm2, Tc = 384 °C, Ec = 14 kV/cm). The relaxor behavior of NKLN-CZ ceramics was induced by the introduction of CaZrO3, which may lead to A-site cation disorder and show diffuse phase transition characteristics. Hence, it broadens the temperature range of phase transformation and mitigates thermal instability for piezoelectric properties in NKLN-CZ ceramics. The value of kp for NKLN-CZ ceramics is held at 27.7-31% (variance of kp < 9%) in the range from -25 to 125 °C. The results indicate that lead-free ceramics NKLN-CZ is one of the hopeful temperature-stable piezoceramics for practical application in electronic devices.

High-temperature transformation behavior of iron-doped titanium dioxide crystal structures

ABSTRACT In this research, high-temperature in situ X-ray diffraction were used to study the high-temperature transformation behavior of the iron-doped titanium dioxide (TiO2). The results show that the phase transformation temperature of TiO2 from anatase (TiO2-A) to rutile (TiO2-R) increased with increasing iron content and that the addition of iron impeded the transformation of titanium dioxide from TiO2-A to TiO2-R, which decreased the TiO2 phase transformation temperature interval. The mechanism is as follows: on the one hand, the incorporation of iron decreases the grain size of both TiO2-A and TiO2-R, and refinement of the grains increases the phase transformation temperature; on the other hand, the Fe3+ infiltrated into TiO2 attracts electron cloud of O atoms,causing O atoms to move towards Fe3+ during the high-temperature phase transformation, causing the crystal defects in TiO2 to accelerate the TiO2-A to TiO2-R phase transformation reaction and decrease the phase transformation temperature range.

Research on falling film dehumidification performance of microencapsulated phase change materials slurry

In the process of liquid desiccant dehumidification, the temperature-rise of the desiccant solution caused by moisture absorption will seriously affect the dehumidification capacity and performance. It is expected that the temperature rise of solution can be restrained by adding microencapsulated phase change materials (MicroPCMs) into the liquid desiccant solution. In this paper, based on computational fluid dynamics (CFD) method, two-dimensional models of flat plate and corrugated plate falling film dehumidification of the microencapsulated phase change material slurry (MPCMS) were developed and validated. The dynamic boundary method was used to determine the interfacial mass transfer coefficient. The influences of several factors on the dehumidification performance, including the concentration of MicroPCMs, the inlet temperature of the MPCMS and the falling film plate configuration, were investigated. The results show that, adding MicroPCMs into the liquid desiccant solution is beneficial to the dehumidification performance improvement. The inlet temperature of MPCMS is a very critical variable. When the inlet temperature of the slurry is in the phase transformation temperature range of MicroPCMs, with the adding of the microcapsule, the temperature rise in dehumidification process can be restrained, and the moisture removal performance can be improved significantly. When the MPCMS inlet temperature is at the phase transformation onset point, and the concentration of MicroPCMs is 5%, the water condensation rate is 14.2% higher than that of the base solution. Moreover, it’s not that the more microcapsules added, the larger mass transfer coefficient is. There is an optimum concentration of MicroPCMs to achieve the maximum interfacial mass transfer coefficient. The corrugated plate configuration is more conducive to the dehumidification enhancement by the MPCMS.

Effect of NiO interface coating on thermal and mechanical properties in Ba&amp;lt;sub&amp;gt;0.8&amp;lt;/sub&amp;gt;Sr&amp;lt;sub&amp;gt;0.2&amp;lt;/sub&amp;gt;TiO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;/Cu matrix composites

Ba0.8Sr0.2TiO3 (BST) particles are an effective reinforcement to reduce the coefficient of thermal expansion of Cu composites because of their negative thermal expansion behavior during phase transformation. However, improving interface bonding is still the key point to further study. In this study, NiO interface coating is employed in the BST/Cu composite to improve interface bonding. NiO interface coating of the composite broadens the phase transformation temperature range of BST particles. Accordingly, the average thermal expansion of the composite in the temperature range of 30–250°C is reduced from 12.99×10−6 to 11.71×10−6 °C−1. In addition, the mechanical properties of the composite are considerably enhanced. In specific, the yield strength and the compressive strength are increased by 72.8% and 41.3%, respectively. This work verifies that NiO interface coating can effectively improve the interface bonding in the BST/Cu composite and further enhance the properties of the composite. The results imply that the NiO-BST/Cu composite has great potential for application in the future.

Effect of cooling rate on α variant selection and microstructure evolution in a near β Ti–5Al–3Mo–3V–2Cr–2Zr–1Nb–1Fe alloy

Abstract The microstructure evolution and selection of α variants in a new near β titanium alloy Ti-5321 (Ti–5Al–3Mo–3V–2Cr–2Zr–1Nb–1Fe) were thoroughly investigated by dilatometry under continuous cooling conditions accompanied with OM, XRD, SEM, EBSD and TEM. Cooling rates from β region to room temperature significantly influenced the microstructure based on the competitive growth of αGB, αWGB and αWI. The low (0.01 °C/s and 0.1 °C/s), intermediate (0.5 °C/s and 1 °C/s) and high (2 °C/s, 4 °C/s and 5 °C/s) cooling rates resulted in bi-lamellar, basket-weave and single metastable-β microstructures, respectively. Moreover, the transformed microtexture was also found in the cooling process at low cooling rate. In addition, a continuous cooling transformation (CCT) diagram obtained by the dilatometric analysis revealed the sensibility of the β→α phase transformation temperature range to the cooling rate. EBSD analysis revealed that microtexture formed by α colonies with the similar orientations, occurred in the adjacent β grains and maintained Burgers orientation relationship (OR) with at least one of the adjacent β grains. Two typical cases, i.e. the single-BOR α colonies (the colonies which maintain Burgers OR with β grain only on one side) and the double-BOR α colonies (α colonies which maintain Burgers OR with both the adjacent β grains) were studied. The single-BOR α colonies corresponded to the different α variants from the parent β grain. The double-BOR α colonies occurred in which the adjacent β grains shared nearly common {110}β plane, moreover, the double-BOR α colonies could possess the identical orientation in the adjacent β grains which have a 60° rotation about a common β direction.

Research and control of network carbide in GCr15 bearing steel

Due to the small amount of transformation during the phase transformation process, it is difficult to determine the phase transition temperature of the proeutectoid cementite in the bearing steel by the expansion method. In this paper, the Gleeble3800 thermal simulator was used to study the phase transformation behavior of GCr15 bearing steel at different cooling rates. Firstly, the phase transformation temperature range of pearlite is about 550 °C ∼ 700 °C measured by expansion method. Based on this, the transformation temperature range of proeutectoid cementite is about 700 °C ∼ 900 °C studied by metallographic method; The precipitation curve of proeutectoid cementite was supplemented, and the complete continuous cooling phase transition curve (CCT curve) of bearing steel was drawn. On this basis, the scheme of inhibiting the formation of proeutectoid cementite by two-stage cooling process was proposed and discussed, and the finishing cooling temperature was studied, which provides a basis for controlling network carbide in field production.

Exploring the functional and corrosion behavior of friction stir welded NiTi shape memory alloy

The friction stir welding was proved to be a promising process to weld NiTi shape memory alloy with adequate mechanical strength and retention of shape memory effect. In this work, the tool wear during welding and the compositional change in the weld cross section has been evaluated. The tensile cyclic behavior for different strain percentages has been investigated. Interestingly, the thermomechanical behavior of the weld was studied using electrical actuation. The actuation was carried out at different current and the actuation temperatures were corroborated with phase transformation temperature range measured using differential scanning calorimetry. A maximum displacement of 17.8 mm was recorded at the actuation current of 5 A. The electrochemical corrosion testing has been performed to understand the corrosion behavior of the friction stir welded NiTi. The weld has exhibited a lower corrosion resistance than the base metal as seen from the lower breakdown potential of 250 mV and a higher current density of 1.5 × 10−4 mA/cm2.

Exploring the functional capabilities of NiTi shape memory alloy thin films deposited using electron beam evaporation technique

The viability of utilizing electron beam evaporation technique for the development of NiTi shape memory alloy (SMA) thin films on kapton polyimide (flexible substrate) has been investigated. The actuation characteristics of the SMA/polyimide structure were evaluated using shape recovery analysis and electrical actuation. The maximum shape recovery ratio of 1.375 was attained with butterfly configuration during shape recovery analysis. The SMA/polyimide stimulated via Joule heating has displayed a maximum displacement of 0.9 mm at 3 V. The surface morphology examined through scanning electron microscope shows the smooth surface without any pores. The thermal stability analyzed using thermogravimetric analysis shows the NiTi SMA thin film can withstand higher temperature above 550 °C without any damage to the SMA/polyimide structure. The stress/strain behavior of the SMA/polyimide structure was analyzed as a function of temperature. The differential scanning calorimetry has showed that the austenite phase transformation temperature lies in the range of 45°C-95 °C. The temperature sweep test performed using dynamic mechanical analyzer recorded a drastic drop in storage modulus in the same phase transformation temperature range as that of DSC. The UV–Vis spectroscopy reveals the NiTi/polyimide structure has high reflective surface in the visible region which aids in the application of reflectors. SMA/polyimide structure can be used as a smart optical mirror in interferometry technique owing to its optical reflectivity.

Effect of temperature-dependent phase transformation on UV detection properties of zinc sulfide nanocrystals

In this work, design and optimization of ultraviolet sensors based on ZnS nanoparticles with the focus on the effect of annealing temperature on optical properties of zinc sulfide were carried out. Synthesis of ZnS nanoparticles was performed using a chemical deposition method and annealing process was followed at 300 °C, 500 °C and, 700 °C under flow of argon. Scanning electron microscopy indicated that by increasing the annealing temperature, the particle size of ZnS nanostructures is increased. Differential thermal analysis showed that the temperature range of phase transformation in ZnS nanostructures is at 300 °C–450 °C. X-ray diffractometry demonstrated a phase change from zinc blende to hexagonal wurtzite at the temperature of 500 °C. The UV-visible spectra of the ZnS samples indicated an increase in light absorption of ZnS nanostructures regarding to the phase transformation at 500 °C. Photoluminescence (PL) study also demonstrated a slight blue-shift in PL peak position of the sample that was annealed at 500 °C which is attributed to the higher optical band gap of this sample. Moreover, the intensity ratio of UV to visible peak is the highest for this sample showing an enhancement in optical properties of ZnS nanostructures which is suitable for fabrication of visible-blind UV detectors. For studying the influence of annealing temperature on optoelectrical properties of UV sensors based on ZnS nanostructures, metal-semiconductor-metal devices were fabricated using deposition of interdigitated Schottky contacts on different ZnS samples. The suitable optical and structural properties of the optimum sample including increasing the electron-hole pairs under UV illumination was manifested in optoelectrical characteristics of ultraviolet detectors based on ZnS sample which was annealed at 500 °C. For this sample, the sensitivity under UV radiation was enhanced by 6.9 times compared to the other ZnS samples.

Reversible elastocaloric effect at ultra-low temperatures in nanocrystalline shape memory alloys

Superelastic shape memory alloys (SMAs) exhibit a reversible elastocaloric effect that originates from a release/absorption of latent heat associated with a stress-induced martensitic phase transformation. In typical SMAs, the conventional elastocaloric effect will vanish when the operating temperature falls below the temperature range in which martensitic phase transformation can be triggered by stress. We report emergence of an unprecedented elastocaloric effect with a decrease of temperature, well below the temperature range of martensitic phase transformation, in a model nanocrystalline NiTi that preserves slim-hysteresis superelasticity at ultra-low temperatures. The new elastocaloric effect emerges at a temperature of ∼90 K, exhibits an opposite sign than the conventional elastocaloric effect, and intensifies gradually with a decrease of temperature to 18 K. At 18 K, a large adiabatic temperature change ΔTad of +3.4 K is measured upon rapid release of tensile stress. The measured ΔTad are larger and extend over a wider temperature span than the existing electrocaloric, piezocaloric, and barocaloric cryo-refrigeration materials. We show that such low temperature elastocaloric effect originates from an entropic elasticity associated with large non-linear elastic deformations of the nanocrystalline microstructure at ultra-low temperatures. Our study suggests a new avenue to cool ultra-low temperature ambients.

High-Pressure Synthesis of High Coercivity Bulk MnAl-C Magnets from Melt-Spun Ribbons

Bulk MnAl-C magnets were prepared via high-pressure compaction of melt-spun ribbons. The e → τ phase transformation (PT) in the melt-spun MnAl and MnAlC ribbons occurs mainly via the massive mode, whereas the displacive mode is not prominent. The massive PT temperatures of the melt–spun MnAl and MnAlC ribbons were measured to be in the range 660–739 K and 700–758 K, respectively. The PT temperatures of the melt-spun MnAlC ribbons are lower than those of water–quenched MnAlC. The annealing process for producing τ-phase from e-phase was optimized based on the measured PT temperature range. As a result, no decomposition of the metastable e/τ-phase MnAl and MnAlC were observed during the optimized high temperature annealing. High-purity τ-phase MnAlC ribbons with high magnetization (122 Am2/kg at 8 T) and low coercivity (0.13 T) were obtained. The coercivity of the bulk MnAlC obtained by high-pressure compaction was significantly enhanced and reached 0.38 T partially due to the grain refinement of the sample during high-pressure deformation.

Regularities of Oxidation and Decarburization of Special Alloy Steels in the BCC→FCC Phase Transformation Temperature Range

Regularities of oxidation and decarburization of special alloy steels 12KhN, 30G1R, 35KhGSA, 40Kh, and 62S2KhA in the temperature range 800–950°C of their phase transformation from ferrite to austenite are investigated. It is established that for all steels there is a general regularity in steady growth of lost metal layer thickness as a result of oxidation with an increase in heating duration and temperature. For special alloy steels, the depth of the decarburized zone decreases (possibly, with a subsequent increase) with an increase in isothermal aging temperature and transition from zones for ferrite existence into austenite. Superposition of these two processes leads to an increase in decarburized zone depth on holding steel in the temperature range of the presence of ferrite. Therefore, in order to prevent the occurrence of decarburized zones that have an unfavorable effect on cold upsetting capacity for round bars, it is expedient to accelerate special alloy steel billet heating to a temperature near 900–950°C.

Influence of strongly textured microstructure on the all-round shape memory effect of rapidly solidified Ni51Ti49 alloy

Ni51Ti49 alloy strip with all-round shape memory effect (ARSME) was obtained through rapid solidification followed by constraint-aging treatment. The high cooling rate and large temperature gradient along the thickness direction of Ni51Ti49 alloy strip yield fine columnar grains and strong fiber texture of <100>B2 during rapid solidification. Such fine-grained and strongly textured microstructure increases the nucleation, limits the orientation and restricts the growth of Ni4Ti3 precipitates during constraint-aging treatment. The fine and well-aligned Ni4Ti3 precipitates with dispersive distribution introduce strong coherent stress field and numerous interfaces between the matrix and precipitates in the rapidly solidified and constraint-aged Ni51Ti49 alloy. Homogeneous composition and massive interfaces in the B2 matrix promote the simultaneity of local phase transformations. The strong coherent stress field and the excellent deformability of <100>B2-oriented grains contribute to large deformation and high recovery ratio of the alloy during phase transformation. Thus, the strongly textured microstructure formed during rapid solidification allows the constraint-aged NiTi alloy to possess superior ARSME with narrow phase transformation temperature range.

Narrow thermal hysteresis of NiTi shape memory alloy thin films with submicrometer thickness

NiTi shape memory alloy (SMA) thin films were fabricated using biased target ion beam deposition (BTIBD), which is a new technique for fabricating submicrometer-thick SMA thin films, and the capacity to exhibit shape memory behavior was investigated. The thermally induced shape memory effect (SME) was studied using the wafer curvature method to report the stress-temperature response. The films exhibited the SME in a temperature range above room temperature and a narrow thermal hysteresis with respect to previous reports. To confirm the underlying phase transformation, in situ x-ray diffraction was carried out in the corresponding phase transformation temperature range. The B2 to R-phase martensitic transformation occurs, and the R-phase transformation is stable with respect to the expected conversion to the B19′ martensite phase. The narrow hysteresis and stable R-phase are rationalized in terms of the unique properties of the BTIBD technique.

Phase-Transformation-Induced Extra Thermal Expansion Behavior of (SrxBa1-x)TiO3/Cu Composite.

The properties of metal matrix composites (MMCs) can be optimized effectively through adjusting the type or the volume fraction of reinforcement. Generally, the coefficient of thermal expansion (CTE) of MMCs can be reduced by increasing the volume fraction of the reinforcement with lower CTE than metal matrix. However, it is great challenge to fabricate low CTE MMCs with low reinforcement volume fraction because of the limitation of reinforcement CTEs. SrxBa1−xTiO3 (SBT) powder presents negative thermal expansion behavior during the phase transformation from tetragonal to cubic phase. Here, we demonstrate that the phase transformation of SBT can be utilized to reduce and design the thermal expansion properties of SBT particle-reinforced Cu (SBT/Cu) composite, and ultralow CTE can be obtained in SBT/Cu composite. The X-ray diffraction analysis on heating indicates that the temperature range of phase transformation is extended greatly, therefore, the low CTE can be achieved within wide temperature range. Landau-Devonshire theory study on the phase transformation behaviors of SBT particles in the composite indicates that thermal mismatch stress significantly affects the Curie temperature of SBT particles and the CTE of the composite. The results given in the present study provide a new approach to design the MMCs with low CTE.

The effects of heating/cooling rate on the phase transformations and thermal expansion coefficient of C–Mn as-cast steel at elevated temperatures

Abstract

Influence of Tensile Training Conditions on Shape-Memory Properties of NiTi-Based Ribbons

This work presents a study of the mechanical properties and influence of thermomechanical training conditions on the two-way shape-memory effect (TWSME) (magnitude and stability) in NiTi and NiTiCu alloys. Correlation with a stress-assisted two-way shape-memory effect (SATWSME) was also investigated. A rapid solidification technique was employed for preparation of small-dimension NiTi samples with homogeneous microstructure. Samples were fabricated by melt spinning. The melt-spun ribbons were trained under tensile deformation by thermal cycling through the phase transformation temperature range. Results showed that the tensile trainings under both constant strain and constant stress were effective in developing a TWSME. The SATWSME was comparable in magnitude to the TWSME. Addition of copper was effective in narrowing the transformation hysteresis and transformation temperature dependence on composition.

Microstructures and damping capacity of TiNiNbMo quaternary alloys with different Ti/Ni ratios

The effect of Ti/Ni ratio on the microstructure, phase transformation characteristics and damping capacity of TiNiNbMo quaternary alloys was investigated by scanning electron microscope, differential scanning calorimetry (DSC) and dynamic mechanical analyser. The microstructure observation showed that eutectic is weakened by the increase in the Ti/Ni ratio. The DSC test indicated that TiNiNbMo alloys with different Ti/Ni ratios exhibit multistage transformations including R transformation and B19′ martensite transformation, and the phase transformation temperature range was increased during cooling or heating. Meanwhile, when the Ti/Ni ratio is equal to 1·08, the alloy in martensite phase exhibited much higher damping than that of Ti50·1Ni49·9 binary alloy, which is mainly attributed to the precipitation of fine and dispersed β-Nb particles in the prime NiTi phases.