Transformation Temperature Range Research Articles

Controlling the optimal phase transition temperature of wires during quenching in salt bath through process parameters

Performing isothermal quenching heat treatment on austenitizing wires in a molten salt-bath can produce high-performance products. Meticulous regulation of the cooling process is essential for enhancing the performance of the wires. The research of this paper is based on the previous achievements of our research group. A three-dimension physical model is built to simulate the cooling process of the wires in the salt-bath. Through this model, this study first designs three new controlling flow hats and compares them with the original controlling flow hats from three perspectives: flow fields, entropy generations, and wire cooling rates, and finally selected the best performing hats. Subsequently, several groups of simulations are conducted under the boundary conditions of different salt capacities, temperatures and wires’ speeds to address the demand for increased capacity of the salt pump in the actual production. The main innovation of this article is to explore the synergistic effect of the salt temperature, capacity and wire speed on the optimal phase transition temperature, and determine the ideal salt temperature under the different salt capacities. In addition, the impact of the salt capacities on the wires’ thermo-uniformity and the range of phase transformation temperature is also studied. Finally, this article provides the molten salt-bath temperatures and wire speeds required to maintain the optimal phase transition temperature under three different salt capacities. This is of great significance for the renovation in actual production.

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.

Effect of adaptive nanocrystalline behaviors on the cavitation erosion performance of Cu47.5Zr45.1Al7.4 bulk metallic glass

Amorphous alloys have attracted much attention in the field of cavitation erosion (CE) due to their good comprehensive properties. However, due to the special amorphous structures that are difficult to characterize, their micro-response behaviors and damage mechanisms during the CE process have not been well elucidated. In this paper, advanced techniques including focused ion beam (FIB) and transmission electron microscope (TEM) were used to comparatively study the microstructure evolution and volume loss rules of Cu47.5Zr45.1Al7.4 and Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glasses (BMG) under the action of cavitation load and cavitation heat to reveal their CE mechanisms. The results showed that the absence of small atoms in Cu47.5Zr45.1Al7.4 led to a large free volume, thereby compromising its hardness, modulus, and yield strength. However, this also made it more susceptible to shear banding, which in turn enhanced its energy absorption capabilities. Although Cu47.5Zr45.1Al7.4 had a higher glass transition temperature (Tg) and onset temperature of crystallization (Tx), as well as a wider supercooled liquid phase region (ΔTx), its exothermic peak was obviously pronounced and the transformation temperature range was significantly narrower. Therefore, it is more likely to adaptively form Cu-rich nanocrystals under the action of cavitation heat. Additionally, the larger free volume in the shear band was conducive to the diffusion of atoms and the occurrence of adaptive nanocrystallization behaviors in Cu47.5Zr45.1Al7.4. These nanocrystals were able to effectively force crack deflection, thereby dissipating impact energy and delaying the fatigue spallation of the material. Consequently, Cu47.5Zr45.1Al7.4 exhibited a far longer incubation period and a noticeably lower cumulative volume loss.

Ru/Ir nanojunctions supported on CNTs as active and ultrastable catalysts for CO preferential oxidation toward hydrogen purification

Hydrogen purification is animportanttechnological step for proton exchange membrane fuel cells (PEMFCs), which can promote the service life of batteries. The preferential oxidation of CO (PROX) in hydrogen is a promising solution for hydrogen purification to avoid poisoning of catalysts by the trace amount of CO present in thehydrogen-richfeedgas. Herein, we demonstrate an interface engineering strategy to prepare Ru/Ir-CNTs nanojunctionswith remarkablecatalyticactivity for CO oxidation. The as-prepared catalyst shows thetotal COconversionin awidetemperaturerange of 50-200℃ under a high feeding gas flow velocity of 72000 mL g-1h−1 and remains stable after 48 h of continuous working. The catalyst also exhibits 100 % CO conversion in temperature from 80 to 100℃ under a much higher feeding gas flow velocity of 108000 mL g-1h−1. Moreover, the CO conversion remains 100 % after intermittent performance testing over a one-week time period. Theoretical calculations reveal that the interface of Ru/Ir can weaken the adsorption of *CO2, thus greatly increasing the temperature range of the complete transformation of CO. Compared to oxide supports, CNTs are more difficult to combine with CO2, which makes the catalyst completely convert CO for a long time within the operating temperature range.

Исследование превращений переохлажденного аустенита при ступенчатой закалке стали 20Cr2Mn2SiNiMo

Currently, step quenching of steels in the temperature range of martensitic transformation, including quenching – partitioning, has found wide application in the automotive industry. Step quenching technology is successfully used to increase a set of properties, which most often include temporary tensile strength and relative elongation. The authors carried out a dilatometric study of the supercooled austenite transformations occurring in the 20Cr2Mn2SiNiMo steel, when implementing various options of step quenching with holding in the martensitic region. It was found that after single-stage quenching, single-stage quenching followed by tempering, and two-stage quenching, primary martensite, isothermal bainite, and secondary martensite are formed in various quantitative ratios. Using X-ray diffraction phase analysis, the amount of residual austenite was determined during step quenching. It has been shown that two-stage quenching makes it possible to stabilise up to 14 % of residual austenite, in the structure of the studied steel, at room temperature. Research has revealed that 20Cr2Mn2SiNiMo steel is characterised by a decrease in the crystal lattice parameter of the residual austenite, with an increase in its content in the steel structure. Uniaxial tensile and impact bending tests were carried out, and the values of the mechanical properties were determined. It has been found that during two-stage quenching, higher strength and elongation values, with lower values of relative contraction and impact strength are achieved compared to oil quenching and low-temperature tempering. The study showed that, with regard to the structural reliability of machine-building parts, step quenching is not the optimal heat treatment mode for the steel under study. The best combination of strength, ductility and impact hardness is achieved after quenching and low-temperature tempering.

Дюрометричний аналіз зміцнення приповерхневого шару ADI при терті під впливом TRIP-ефекту

Features of strengthening of the near-surface layer of ADI during friction due to strain-induced martensitic transformation were analyzed by duromeric methods. Indentation under continuous loading (Meyer hardness, HM) and Vickers microhardness Hμ were used. Pop–ins are observed on the ADI continuous load curves, which indicate martensitic transformations during indentation. The effect usually exists at a load of ~0,1 H and an depth of ~1,5 μk. The average microhardness of the initial sample is Hμ ≈ 4,89 GPa. After wear, the average value increases to Hμ ≈ 6,92 GPa. Statistical analysis of the microhardness distribution of the sample after wear revealed that a third of the indentations have abnormally high hardness, which is characteristic of deformation-induced martensite. Probably, these indents are obtained from regions of the structure where deformation-induced martensitic transformation took place. Increasing the indentation load practically does not affect the determination of the microhardness of the initial sample, but reduces the hardness of the sample after wear. This indicates the gradient nature of deformation and phase-structural rearrangements in the near-surface layer during wear. As the friction temperature increases, there is a decrease in microhardness in the wear zone. This is explained by the departure from the temperature range of the martensitic transformation, due to which the TRIP effect is weakened. The maximum degradation of microhardness is observed between room temperature and 50 oC. Keywords: ADI materials, durometric studies, TRIP-effect, wear.

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.

Structure, microstructure and magneto-elastic property study on Co40Ni29Al31 ferromagnetic shapememory alloy ribbon

Ferromagnetic shapememory Alloys having huge magnetic field and stress-induced strain are suitable materials for sensors and actuators. Ni2MnGa being the prototype of these materials and because of its brittleness alternative systems CoNiAl/Ga were recently developed. CoNiAl being a ductile material because of its two-phase microstructure and the large range of transformation temperatures. In this line, a ribbon with nominal composition Co40Ni29Al31 was prepared using melt-spun technique. The structure and microstructure of the sample was determined using XRD and SEM. The transformation temperatures were determined using four probe method using a cryocooler within the temperature range of 4 K to 350 K. The elastic and magneto-elastic properties were studied using a Vibrating reed method within the temperature 80 K to 300 K. A constant magnetic field of 300 Oe is applied with a coil wound on the cryostat of the vibrating reed setup. As was expected the sample has two phases of microstructure, from the XRD data, a high amount of β phase with a few amount of γ phase was found and it was also replicated in SEM photographs. The phase fractions were found by fitting the XRD data with Reitveld refinement. The transformation temperatures of the sample were obtained from the four probe resistivity measurements, and they are TMs = 133 K, TMf = 83 K, TAs = 130 K and TAf = 179 K. From the sound velocity and internal friction study without and with the magnetic field interesting results were found. The martensitic and inter martensitic transformations were suppressed with the application of magnetic field. It was clearly seen in the sound velocity change plots as a function of temperature and the same was replicated in the internal friction plots. Such studies through light on the magneto-elastic coupling-related issues and are quite useful for the application of these materials for the Micro Electro Mechanical Systems at different operating conditions.

Research of the unacceptable defects causes in the manufacture of reinforcing rope

In the production of reinforcing ropes, the patenting of wire rods is carried out under the technical production regulations. Patenting is a consequence of isothermal treatment, in which the decomposition of supercooled austenite is carried out in the lower part of the temperature range of diffusion transformation. In the microstructure of patented steel, there should be no structures of prostate, bainite, and martensite. Such a structure has a combination of ductility as well as good deformability with high reduction ratios. In the production of ropes, failure to comply with these technical requirements can lead to serious consequences. The article examines the defects that have arisen in the production of reinforcing ropes. In the course of the study, on the surface where the wires broke, uneven colors, scratches, and small flaws were revealed. For microstructural analysis of the metal was used Microscope Altami MET 1C. As a result of the microstructural study of steel, areas with large-lamellar perlite were identified, which led to a wire break.

Experimental Investigation on the Inhomogeneities of Transverse Microstructure and Internal Stress of High‐Strength Low‐Alloy Hot‐Rolled Strip

Herein, the evolution of transformation in the width direction of high‐strength low‐alloy hot‐rolled strip is studied by using thermomechanical simulation, and the temperature, microstructure, and internal stress are correlated based on electron backscatter diffraction data. The temperature and time range of the transverse transformation are determined based on the thermal expansion curve. The results show that the transformation at the edge of the steel plate ends earliest and that at the plate center begins at the latest; only 31.9% austenite undergoes transformation at the plate central by the end of laminar cooling. The fraction of transformed austenite at the plate center is the least throughout the laminar cooling process. The proportion of small grains (within the grain size range of 0–4 μm), mean, and variant coefficient of grain sizes at the plate edge are 75%, 4 μm, and 1.29, respectively. In contrast, those values of the central region are 66%, 4.4 μm, and 1.05, respectively. The correlation between temperature and internal stress evolutions is established. It is demonstrated that the internal stress increases monotonically with the average transformation rate.

Effect of Cr on Isothermal Structure Transformation of Iron Oxide Scale

Herein, the effect of different contents of Cr on the isothermal structure transformation of FeO is systematically studied by a thermogravimetric analyzer, and it is found that the temperature range of eutectoid transformation of FeO in Fe–Cr alloy is 300–500 °C. Combined with the experimental data, the kinetic model of isothermal phase transformation of FeO is established based on Johnson–Mehl–Avrami–Kolmogorov equation, and the time–temperature–transformation curve of isothermal transformation of FeO is predicted, which follows the law of C curve, and the C curve shifts backward with the increase of Cr content. Therm‐calc thermodynamic software calculates the Fe–O phase diagrams of different Cr contents. Combined with the experimental results, the effect mechanism of Cr content on FeO eutectoid transformation is clarified. With the increase of Cr content, the stability of FeO decreases, and under the same isothermal temperature and time, high Cr content has greater undercooling, a higher driving force of phase transition, and the starting time of eutectoid transformation is earlier than that of lower Cr content.

Формирование микроструктуры типа «ожерелье» методом ковки в сплавах Гейслера системы Ni-Mn-Ga-Si как способ повышения механических свойств

The standard technique for melting Heusler alloys involves melting in an argon-arc furnace on a water-cooled copper crucible. As a result of intensive crystallization of the ingot, large elongated crystals are formed in the structure. The thermo-mechanical treatment of such a structure is ineffective, since microcracks are formed along the boundaries of large crystals as a result of internal stresses and martensitic transformation, along which then, during processing, cracks develop and the workpiece is destroyed. It is shown that additional heat treatment by the vacuum induction remelting makes it possible to eliminate this effect. As a result of the treatment, an equiaxed granular microstructure with a grain size of about 200 μm is formed. However, as a result of remelting in a quartz crucible, silicon atoms diffuse into the bulk of the ingot. Its content varies in the range of 1-2% depending on the duration of exposure in the molten state. A uniform distribution of silicon, without the formation of additional phases is shown by energy-dispersive analysis. Thus, the Ni54.1Mn19.6Ga24.6Si1.7, Ni56.2Mn18.8Ga23.2Si1.8, Ni57.4Mn18.2Ga22.7Si1.7 and Ni56.5Mn20.1Ga22.3Si1.2 alloys were obtained. A partially recrystallized structure of the "necklace" type was formed in the alloys by the multiaxial isothermal forging at 950-973 K and the true degree of deformation e=1.9...3.9. The initial large grains with a size of 100-200 microns are surrounded by a layer of fine-grained structure. The thickness of the interlayer at the periphery of the workpiece is about 5 grains. In the center of the workpiece, the proportion of the fine-grained structure may prevail over the coarse-grained structure. The study of cyclic and fatigue strength was carried out by the method of three-point bending during cyclic tests in the temperature range of martensitic transformation using the example of the Ni54.1Mn19.6Ga24.6Si1.7 alloy in the initial state and the Ni57.4Mn18.2Ga22.7Si1.7 alloy in the forged state. It is shown that the “necklace” type microstructure, compared to the equiaxed microstructure, demonstrates a twofold advantage in cyclic strength and a fivefold advantage in fatigue strength.

Detection of structural phase transition in SMART microwires using Magneto-Impedance sensing

• Correlation between the structural transition and magneto-impedance is shown. • A well-defined variation (6%) of magneto-impedance effect is appeared. • Magneto-Impedance effect can be used for phase\strain detection in SMA. We report on the possibility to use magneto-impedance effect to study the structural phase transformation of glass coated Ni 2 FeGa microwires. These microwires show martensitic phase transition within the temperature range from 300 to 350 K. Hysteresis loops confirm the variation of easy magnetization axis direction connected to martensitic transformation . Being parallel to the wire’s axis in high-temperature austenite phase, it is tilted a little bit out of the easy axis for low temperature martensite phase. The temperature dependence of magnetoimpedance effect shows well-defined variation (6%) of impedance that appears within the temperature range of structural transformation as a result of the easy axis variation. These properties give the microwire function of very sensitive SMART actuators since they have also sensing functionality due to the possibility to use magneto-impedance for sensing the structural transformation.

Effect of alloying constituents on thermal, microstructural, mechanical and shape memory properties of Cu-Al-Ag shape memory alloys

PurposeThe purpose of this study is to assess the influence of Al and Ag addition on thermal, mechanical and shape memory properties of Cu-Al-Ag alloy.Design/methodology/approachThe material is synthesized in a controlled atmosphere to minimize the reaction of alloying elements with the atmosphere. Cast samples were homogenized, then subjected to hot rolling and further betatized, followed by step quenching. Eight samples were chosen for study among which first four samples varied in Al content, and the next set of four samples varied in Ag composition.FindingsThe testing yielded a result that the increase in binary alloying element decreased transformation temperature range but increased entropy and elastic energy values. It also improved the shape memory effect and mechanical properties (UTS and hardness). An increase in ternary alloying element increased transformation temperature range, entropy and elastic energy values. The shape memory effect and mechanical properties are enhanced by the increase in ternary alloying element. The study revealed that compositional variation of Al should be limited to a range of 8 to 14 Wt.% and Ag from 2 to 8 Wt.%. Microstructural and diffraction studies identified the ß’1 martensite as a desirable phase for enhancing shape memory properties.Originality/valueNumerous studies have been made in exploring the transformation temperature and phase formation for similar Cu-Al-Ag shape memory alloys, but their influence on shape memory effect was not extensively studied. In the present work, the influence of Al and Ag content on shape memory characteristics is carried out to increase the design choice for engineering applications of shape memory alloy. These materials exhibit mechanical and shape memory properties within operating ranges similar to other copper-based shape memory alloys.

Structure, Martensitic Transformation, and Damping Properties of Functionally Graded NiTi Shape Memory Alloys Fabricated by Laser Powder Bed Fusion.

Besides the unique shape memory effect and superelasticity, NiTi alloys also show excellent damping properties. However, the high damping effect is highly temperature-dependent, and only exists during cooling or heating over the temperature range where martensitic transformation occurs. As a result, expanding the temperature range of martensite transformation is an effective approach to widen the working temperature window with high damping performance. In this work, layer-structured functionally graded NiTi alloys were produced by laser powder bed fusion (L-PBF) alternating two or three sets of process parameters. The transformation behavior shows that austenite transforms gradually into martensite over a wide temperature range during cooling, and multiple transformation peaks are observed. A microstructure composed of alternating layers of B2/B19′ phases is obtained at room temperature. The functionally graded sample shows high damping performance over a wide temperature range of up to 70 K, which originates from the gradual formation of the martensite phase during cooling. This work proves the potential of L-PBF to create NiTi alloys with high damping properties over a wide temperature range for damping applications.

Damage of the martensite interfaces as the mechanism of the martensite stabilization effect in the NiTi shape memory alloys

The aim of the paper was a comprehensive experimental study of the martensite stabilization effect (MSE) in NiTi alloys under various conditions to find the mechanism behind this phenomenon. The MSE was studied in the quenched Ni50Ti50 and Ni51Ti49 alloys subjected to pre-deformation to various strains in three ways: deformation in the martensite state, cooling under stress through a temperature range of the forward transformation and deformation in the austenite state due to the stress-induced martensite formation. It was found that after pre-deformation by the martensite reorientation, the MSE was observed even after a small pre-strain. After pre-deformation by cooling under stress or by stress-induced transformation, the MSE was small if the pre-strain was less than 5%; otherwise, the value of this effect was significant. A new mechanism of the martensite stabilization effect was considered. It was assumed that the damage to the martensite boundaries during the pre-deformation (without plastic strain) decreased their mobility and a larger thermodynamic force needed to be provided to move the interfaces during the reverse transformation.

Phase transformation and mechanical properties of ultrahigh strength steels under continuous cooling conditions

The present work deals with phase transformation mechanical behavior and of newly developed ultrahigh strength steels. Bainitic and martensitic phase transformations have been studied in detail with respect to their transformation temperature range and microstructural evidences observed under various continuous cooling conditions. The various critical temperatures of Ac1, Ac3, Bs, Ms, and TNR of the investigated steels were initially calculated using numerical equations and validated with experimental results. The dilatometric tests consisted under different cooling rates from 0.1 to 100 °C/s and the respective continuous cooling transformation (CCT) diagrams have been determined. The microstructural features were revealed using optical and different electron microscopy techniques. A strong dependency of cooling rate on microstructure and mechanical properties has been found. The present steels have exhibited ultrahigh strength (1400–2000 MPa) with reasonable ductility (6–13% total elongation), which is attributed to combination of mixed microstructure comprising fine bainite and lath martensite along with thin film-like retained austenite. Fine precipitates of (Ti, Nb)C, Mo2C and/or Cu contribute to strengthening effect by increasing the hardness and strength values for a particular cooling rate. It has been witnessed that the hardness, yield strength and ultimate tensile strength have been increased with the rise of both cooling rate and carbon contents.

Data-driven shape memory alloy discovery using Artificial Intelligence Materials Selection (AIMS) framework

One of the obstacles to the deployment of shape memory alloys (SMAs) in solid-state actuation is the low efficiency and functional instability due to the transformation thermal hysteresis and large temperature ranges during martensitic phase transformation. Numerous studies have been conducted in an effort to minimize the thermal hysteresis and transformation temperature range of SMAs through ternary and quaternary alloying of known binary alloy systems, such as NiTi, and considerable success has been achieved. However, and crucially, the alloys discovered so far have failed to maintain a narrow hysteresis under applied stress. In the present study, an AI-enabled materials discovery framework was successfully used to identify both SMA chemistries and the associated thermo-mechanical processing steps that result in narrow transformation hysteresis and transformation range under an applied stress. The major elements of the proposed workflow are described in detail and its materials-agnostic character makes it widely applicable to other alloy discovery challenges. Using this framework, and without relying on subsequent experimental exploratory analysis, an SMA composition, i.e. Ni32Ti47Cu21 (at. %), was predicted and confirmed to have the narrowest thermal hysteresis and transformation range under stress achieved thus far for a NiTi-based SMA. Furthermore, the alloy was shown to exhibit excellent cyclic stability and actuation strain. The methodology and the dataset introduced here can be extended to design novel SMAs with other target functions.

Diffusion welding of titanium using pressure at the initial stage

As an example of alloy OT4 it is shown, that at diffusion welding of titanium alloys with the original globular (equiaxed fine-grained) microstructure, the accumulated strain value of the welded blanks can be reduced (more than 2 times) if the welding process is performed in the temperature range of polymorphic transformation (∼950 °С). In such a case, use the welding pressure only at the first stage to form a physical contact with an area of at least 50% of the nominal, and then produce an isothermal annealing without pressure, the duration of which is temperature dependent. When using a temperature higher than the end of polymorphic transformation (∼1000 °C), the duration of annealing is reduced by almost 10 times compared with annealing at 950 °C.