Phase Transformation Temperature Research Articles

Effect of Accumulative Roll Bonding Cycles and Postprocessing Heat Treatment Temperature on Shape Memory Properties of Cu–Al–Ag Alloys

Herein, Cu/Al/Ag‐layered composites with two silver powder concentrations (2 wt% and 3 wt%) are fabricated with the aid of accumulative roll bonding (ARB). The ARB‐ed samples are heat treated at different temperatures (750, 850, 950, and 1050 °C), times (30, 45, and 60 min), and cycles (1–9 cycles) to produce Cu–Al–Ag shape memory alloys. The samples are characterized by X‐ray diffraction, scanning electron microscope, and electron backscattering diffraction. Phase transformation temperatures are measured by differential scanning calorimetry. Strain recovery and shape memory behavior are evaluated by bending and tensile tests, respectively. The results indicate that alloys containing 2 wt% Ag, rolled till 9 cycles, heat treated at 950 °C for 60 min, and samples with 3 wt% Ag, fabricated by 9 cycles, annealed at 850 °C for 60 min show maximum β martensite phase amount. The strain recovery ratios of the first and second samples are 71.7% and 71.2%, respectively. Additionally, the tensile test shows that the residual plastic strain and the recovered strain for the first sample with 2 wt% Ag are equal to 0.7% and 3.0%, respectively. These results for the second sample with 3 wt% Ag are 1.2% and 3.4%, respectively.

Synchrotron EDXRD strain-temperature measurement during laser welding

Synchrotron EDXRD strain-temperature measurement during laser welding

CALPHAD-Based Modeling and Experimental Validation of Silicon Effect on the Solidification Behavior of Novel SiNb Cast Irons

AbstractThe low oxidation resistance of SiMo ductile cast irons used as exhaust manifold material at high temperatures necessitates the development of new generation ductile cast iron compositions. New alloy designs can be made using CALPHAD methodology, and solidification sequence, segregation and critical phase transformation temperatures can be determined, especially for the solidified bulk materials. Thus, in commercial practicality, castable compositions with a raised A1 temperature can be obtained. In this study, novel SiNb cast irons with varying silicon contents were developed as candidate materials for exhaust manifolds. Solidification sequence, microsegregation, phase transformations, equilibrium phases of hypereutectic compositions containing 4 to 7 wt pct Si were calculated by CALPHAD-based modeling. The bulk materials of the studied compositions were cast as Y blocks and metallurgical analyzes were carried out. Studies revealed that; (i) in the ferritic matrix of the cast irons, graphite, Nb-rich carbides and some pearlite existed, (ii) pearlite formation was due to the negative segregation of silicon and positive segregation of manganese during solidification, (iii) as silicon content increased the amount of silicon dissolved in ferrite phase increased in the solidified structure and as a result pearlite formation decreased at the cell boundaries, and amount of vermicular graphite increased, (iv) depending on the silicon content the critical A1 temperature varied between 860 °C to 1013 °C and these values were higher than that of SiMo cast iron. All these findings revealed that SiNb cast irons had phase stability at higher temperatures compared to SiMo cast iron.

Electron paramagnetic resonance and luminescence spectroscopy of transition metal ion impurities and X-ray-induced radicals in brushite

Calcium phosphates hold paramount importance as the constituents of hard tissue of living organisms. Among them, brushite (CaHPO4·2H2O), also known as dicalcium phosphate dihydrate (DCPD), is a common precursor in phosphate synthesis and is becoming increasingly appealing as a biomaterial for bone regeneration applications. This study presents a comparative analysis of structural, morphological, thermal, and spectroscopic properties of synthetic brushite prepared by the wet precipitation method with several brushite products available from commercial vendors. Electron paramagnetic resonance (EPR) spectroscopy revealed that Mn2+ and Fe3+ ions are common trace impurities in commercial products. Following exposure to X-rays, EPR signals of several phosphorous-related radicals emerge. The annealing of the irradiated samples gives rise to broad thermally stimulated luminescence (TSL) signals in the 40-120 °C range, which correlates with the annealing kinetics of the radicals. The stability of radiation-induced EPR and TSL signals is limited by the phase transformation temperature from brushite to monetite (CaHPO4). The results of this study provide novel insights into the formation and stability of phosphorous-related radicals and demonstrate how minuscule amounts of impurity ions can strongly influence the spectroscopic properties of brushite.

Low temperature effect on cyclic behavior of shape memory alloy U-shaped dampers

Although Nickel-Titanium (NiTi) shape memory alloys (SMAs) have been widely studied as seismic response mitigation devices in civil structures, their temperature sensitivity due to the coupled thermo-mechanical behavior prevents their practical implementation in cold temperature environments. This paper investigated the effects of varying ambient temperatures (particularly low ambient temperature) on the hysteretic behavior and self-centering (SC) ability of shape memory alloy U-shaped dampers (SMAUDs) that were made of NiTi showing superelasticity (SE) at room temperature. Thermo-mechanical properties of SMAUDs were identified through differential scanning calorimetry (DSC) tests. Cyclic loading experiments on SMAUDs were conducted at a wide ambient temperature range from −40°C to 20°C. The variations in the hysteretic characteristics of the SMAUD, including partial superelasticity (SE), strength, stiffness, SC, and energy dissipation capabilities, at different ambient temperatures were investigated. In general, the decreasing ambient temperature leads to the degradation of the SC ability. At ambient temperatures below the phase transformation temperature, the SMAUDs lose the SE but still maintain certain levels of strength and energy dissipation, which is different from common axial-type SMA elements. Meanwhile, the SMAUDs can restore their SC ability and strength after the recovery from low temperatures to room temperature, making them suitable for use in a cold environment.

Electro–Thermo–Mechanical Characterization of Shape Memory Alloy Wires for Actuator and Sensor Applications, Part 2: High‐Ambient‐Temperature Behavior

The typical phase transformation temperatures of commercially available shape memory alloys (SMA) for actuator applications are in the region of 80–90 °C for austenite finish and around 60 °C for martensite start. That limits the areas of application for SMA actuators, as increased ambient temperatures restrict their functionality. Especially in the industrial and automotive sectors, operational temperatures of 80 °C and higher are commonly required. This article discusses the limits of operation temperatures for commercially available SMA actuator wires. Also, methods to increase this critical temperature limit, at which the SMA actuation strain falls below a certain threshold, are proposed. By means of electrothermal actuation experiments, the influence of the variation of bias loads and an additional training method are investigated. Supported by these results, an exemplary valve actuator system is designed, which exhibits consistent stroke in a wide range of ambient temperatures. All experiments and measurements are conducted on a custom designed test bench with the same commercially available SMA wire. The test bench is in the following used again to evaluate the designed SMA valve actuator.

Wire-based electron beam additive manufacturing of NiTiNb shape memory alloy: Microstructure, phase-transformation behavior and mechanical properties

NiTiNb shape memory alloy (SMA) is considered to have great potential in aerospace due to its wide phase-transformation hysteresis. Here, we innovatively used electron-beam additive manufacturing (EBAM) to fabricate a NiTiNb SMA thin-walled structure. The phase-transformation temperature, microstructure evolution, and mechanical properties were investigated in detail. The as-built NiTiNb SMA comprised a NiTi matrix and different morphologies of β-Nb phase at room temperature. The microstructure homogeneity and mechanical properties of NiTiNb prepared by EBAM significantly improved compared with those of NiTiNb powder-based AM technology. Our work provided a promising method for the preparation of defect-free and microstructure homogeneous NiTiNb SMA by AM. This method further stimulated the potential of additively manufactured SMA components for industrial applications.

Effect of Fe Composition and Heat Treatment Temperature on the Transformation Temperature of R-Phase of Ti-Ni-Fe Alloy

R-phase transformations in TiNi shape memory alloys (Nitinol) have various applications because of their small thermal hysteresis and low fatigue resistance. Adding a third element such as Fe or Al is one of the useful ways to induce R-phase transformation. Controlling the R-phase transformation temperature is crucial for industrial and bio-field applications. However, the effects of adding Fe have rarely been reported. In this study, the effects of Fe addition and heat treatment temperature on the R-phase transformation temperature of TiNiFe shape memory alloys were systematically investigated. Results showed that increasing Fe composition decreases the R-phase and martensitic transformation temperatures of 19K/1at%Fe and 51 K/1at%Fe, respectively. Additionally, in the Ti–49Ni–1Fe alloy, rather than a martensite transformation, the R phase transformation temperature was constant irrespective of heat treatment temperature and increasing number of thermal cycles. This means that the R-phase transformation temperature is not affected by dislocation density resulting from the heat cycling or cold working processes. This allows practical applications of R-phase transformation to be easily realized. Furthermore, this means that the R-phase transformation temperature is only affected by the Ni content of the matrix.

Achieving excellent strength-ductility-superelasticity combination in high-porosity NiTiNb scaffolds via high-temperature annealing

Metallic scaffolds with lightweight, low elastic modulus, and high energy-absorbing capacity are widely utilized in industrial applications but usually require post-heat treatment to enhance their comprehensive mechanical properties. However, it is unclear how to utilize the impact of β-Nb on the surrounding matrix for NiTiNb ternary alloys to achieve strength-ductility-superelasticity enhancement. Here, we prepared rhomboidal dodecahedral NiTiNb porous scaffolds with a porosity of 85.9% by additive manufacturing. Subsequently, annealing treatment was employed to drastically reduce the phase transformation temperatures and expand the thermal hysteresis. Interestingly, the 850°C annealed scaffold exhibited exceeding double compressive strength of the as-built sample, with a remarkable improvement in ductility and superelasticity. From the microstructure perspective, high-temperature annealing caused a further eutectic reaction of the unmelted Nb particles with the NiTi matrix and the transformation of mesh-like β-Nb into diffuse spherical β-Nb particles. The microstructure evolution after deformation indicated that stress-induced martensitic transformation occurred in the matrix away from the NiTi-Nb eutectic region whereas almost no martensite formed nearby β-Nb particles. Atom probe tomography characterization revealed an element diffuse zone in several nanometers surrounding the β-Nb particle, where the substitution of Nb with Ti led to a higher Ni: Ti atomic ratio, lowering transformation temperatures. Molecular dynamics simulations illustrated that β-Nb particles can not only entangle dislocations internally, acting as reinforcements but also hinder the twin growth, contributing to strain hardening. This work elucidates the influence of β-Nb particles on the deformation mechanism of the NiTi-Nb eutectic region through in-depth atomic-scale investigation, which can provide inspiration for the improvement of comprehensive mechanical properties of NiTiNb alloys.

Postweld Heat Treatment of 15Cr-6Ni-2Mo-1Cu Supermartensitic Stainless Steel Welds

Supermartensitic stainless steels with 15Cr- 6Ni-2Mo-1Cu with 135 ksi minimum yield strength (15Cr-135 SMSS) offer high strength and good toughness through a complex hierarchical microstructure of nanoscale precipitates, tempered martensite, and reverted austenite. Upon welding and postweld heat treatment, substantial changes to heat-affected zone microstructure and hardness may occur. Here, we reveal spatially heterogeneous microstructure and microhardness in the HAZ of 15Cr-135 SMSS; correlate these changes to measured phase transformation temperatures; and demonstrate that HAZ hardness changes depend strongly on postweld heat treatment temperatures. Furthermore, we demonstrate that PWHT may lead to undesired reductions in base metal yield strength and formulate a design guide for PWHT that quantifies the trade-offs in desired reductions of HAZ hardness with undesired changes to base metal yield strength. These findings have important practical implications for welding procedure design and qualification.

CALPHAD simulation and experimental study on heat treatment process of Al-Cu-Mn-Mg-Sc cast alloys

Because different heat treatment parameters have different effects on the microstructure and mechanical properties, it is necessary to optimize the heat treatment parameters to obtain alloys with better properties. In this study, the heat treatment parameters of Al-Cu-Mn-Mg-Sc cast alloys were optimized by using thermal simulation and experimental methods. The results show that the phase transformation temperature of the low melting point eutectic phase Al2Cu is 542.9 ℃, and the time for element homogenization distribution of the alloy during solid solution at 525 ℃, 535 ℃ and 550 ℃ is 8 h, 7 h and 4.5 h, respectively. With the rise of solid solution temperature, the microhardness increase at first and then decrease, and the microhardness reaches to 96.4 HV at 535 ℃. When solid solution heat treatment is carried out at 535 ℃ for different times, the microhardness increase at first and then decrease with time, and the microhardness reaches to 118.4 HV at 5 h. It is known that the number of metastable phase decreases gradually with the increase of aging heat treatment temperature by using the calculation of thermodynamic software. The optimal aging heat treatment process parameter for the alloy is 170 ℃ for 10 h, and the microhardness at this time reaches to 142.3 HV.

A Study of a Cryogenic CuAlMn Shape Memory Alloy

In extreme temperature environments, a newly emerging engineering application involves both the active and passive control of structures using cryogenic shape memory alloys, which are smart materials able to recover high deformation below the freezing point. With the objective of carrying out new advances in this area, the present work aims to investigate the Cu-7.5Al-13.5Mn (wt.%) shape memory alloy. Thermal, microstructural, and thermomechanical analyses of as-cast and hot-rolled specimens were performed, taking into account the effects of annealing and solubilization. It was observed that the phase transition occurs at temperatures below 120 K and changes according to the thermo-mechanical path. Specifically, hot-rolling lowers the phase transition temperature range with respect to the as-cast condition–from 34 K to 23 K for Mf, and from 89 K to 80 K for Af. Additionally, when the annealing temperature rises, the phase transformation temperature increases as well, and the alloy loses its cryogenic features when heat treated above 473 K. Finally, loss factors of 0.06 and 0.088, which were respectively found in dynamic and static settings, validate the material’s good damping response.

Synthesis and phase transformation study of nanostructured manganese oxide polymorphs

This paper presents the green synthesis of manganese oxide nanoparticles using olive leaf extract (OLE). The extract functions as both a reducing agent, responsible for converting manganese ions into nanoparticles, and a capping agent, aiding in stabilizing the formed nanoparticles. Our focus lies on investigating the thermal stability, phase transformation, and decomposition temperatures of different manganese oxide phases in powder form as a function of the calcination temperature. Since phase transformation depends on temperatures change at the nanoscale both thermogravimetric and differential scanning calorimetry (TGA, DSC) are used to determine the new phase transformation temperatures of the synthesized nanoparticles. Moreover, the phase structure and the exact stoichiometry are studied using ex-situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning/transmission electron microscopy (SEM/TEM). XRD and XPS analyses reveal the formation of amorphous MnOx at room temperature (prior to calcination), transitioning to crystalline phases (Mn2O3 and Mn3O4) post-calcination. High-resolution TEM and SEM depict the formation of nanoparticles around 15 nm in size, exhibiting different shapes. BET technique calculations give a very high specific surface area, rending these nanoparticles excellent candidates for several applications.

Numerical Simulation and Experimental Verification of the Quenching Process for Ti Microalloying H13 Steel Used to Shield Machine Cutter Rings

Owing to the non-uniform distribution of chemical composition and temperature during the heat treatment process, the residual stress and deformation of the workpiece emerge as crucial factors requiring consideration in managing the service performance and lifespan of shield machine cutter rings crafted from H13 steel. Considering H13 steel with titanium microalloying as the research object for the shield machine cutter ring, we simulate the quenching process using Deform-3D. The temperature field, phase transformation, stress evolution, and deformation amount after quenching are analyzed. The results demonstrate a strong agreement between the simulation and experimental results, offering valuable insights for optimizing the heat treatment process and enhancing the overall performance of shield machine cutter rings.

Phase Transformation Temperature Prediction in Steels via Machine Learning.

The phase transformation temperature plays an important role in the design, production and heat treatment process of steels. In the present work, an improved version of the gradient-boosting method LightGBM has been utilized to study the influencing factors of the four phase transformation temperatures, namely Ac1, Ac3, the martensite transformation start (MS) temperature and the bainitic transformation start (BS) temperature. The effects of the alloying element were discussed in detail by comparing their influencing mechanisms on different phase transformation temperatures. The training accuracy was significantly improved by further introducing appropriate features related to atomic parameters. The melting temperature and coefficient of linear thermal expansion of the pure metals corresponding to the alloying elements, atomic Waber-Cromer pseudopotential radii and valence electron number were the top four among the eighteen atomic parameters used to improve the trained model performance. The training and prediction processes were analyzed using a partial dependence plot (PDP) and Shapley additive explanation (SHAP) methods to reveal the relationships between the features and phase transformation temperature.

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.

Influence of copper on the microstructure and mechanical properties of titanium ortho-alloy produced by selective laser melting

This study explores an intermetallic orthorhombic titanium alloy produced by incorporating varying copper concentrations ranging from 0 to 6 wt. % through in-situ doping during selective laser melting (SLM) fabrication, coupled with simultaneous substrate preheating. The investigation delves into the influence of copper introduction on grain refinement within the primary B2/β-phase and subsequent alterations in mechanical properties. Through X-ray diffraction analysis and scanning electron microscopy, the microstructure characterized by the presence of the B2/β-phase and orthorhombic phase precipitates was identified. Additionally, the detection of a minor quantity of the α2-Ti3Al-phase was noted, with its proportion increasing proportionally with the augmentation of copper content. Differential scanning calorimetry revealed a shift in the phase transformation temperatures towards higher temperatures and a constricted α2-Ti3Al + B2/β + Ti2AlNb region, attributed to the inclusion of copper. The addition of copper, up to 6 wt. %, resulted in the softening and embrittlement of the orthorhombic alloy, forming a fine-grained microstructure with an average grain size of 8.3 μm. Energy dispersive X-ray spectroscopy confirmed the presence of an intermetallic O-phase along the grain boundaries, contributing to a 12 % increase in hardness compared to the orthorhombic alloy without copper after SLM with substrate heating at 850 °C. An alloy containing 4 wt. % copper exhibited superior plastic properties and a tensile strength of 1080 MPa, comparable to the strength of the orthorhombic alloy obtained via SLM followed by hot isostatic pressing.

Predictive modeling of phase transformation temperatures in NiTiCu shape memory alloys: Integrating electronic factors through artificial neural network

The primary objective of this research is to investigate the correlation between the electronic factors of NiTiCu Shape memory alloy (SMA) on phase transformation temperature (PTT) and thermal hysteresis. The study yields valuable insights into understanding the phase transition behavior of NiTiCu shape memory alloys, emphasizing the intricate interplay between electronic factors and alloy composition on PTT. Theoretical analyses highlight the critical role of considering electronic structure in designing shape memory alloys. A pivotal aspect of this study is the development of an artificial neural network (ANN) model to predict PTT, encompassing austenite start (As), austenite finish (Af), martensite start (Ms), martensite finish (Mf), and thermal hysteresis is calculated from the predicted PTT. This research draws on datasets from prior studies on diverse ternary NiTiCu SMA compositions, focusing exclusively on homogenized, solution-treated data to mitigate precipitate-induced impacts on PTT. The proposed ANN model, configured with 9–14–4 neurons, demonstrates precise and reliable predictions for PTT in NiTiCu. The model's robust performance, characterized by a strong correlation (high R values), low relative errors within ±1% from the Gaussian distribution, and successful validation, underlines its applicability for predicting PTT across diverse NiTiCu compositions. Furthermore, experimental validations for unseen NiTiCu compositions affirm the model's reliability and robust performance in forecasting PTT in NiTiCu SMAs.

The effect of Hf on the microstructure, transformation temperature, and the shape memory properties of Zr–Cu-based high-entropy shape memory alloys

The microstructures, phase transformation temperatures, and shape memory properties of Hf-modified Zr50−xHfxCu25Ni7.5Co17.5 and Zr50−xHfxCu25Ni10Co15 high-entropy shape memory alloys (SMAs) were investigated. Hf additions can alter the valence electron concentration, strengthen the alloy matrix, and introduce more secondary phase particles, which significantly influence the properties of the alloys. The results reveal that high austenitic transformation temperature (over 600 K) with very small thermal hysteresis (70–80 K) can be achieved by tailoring the Hf contents, and the best shape memory recovery strain (up to 2.44%) compared with other Zr–Cu-based SMAs could be obtained in Zr42Hf8Cu25Ni10Co15 alloy. This study demonstrated that high-performance Zr–Cu-based high-entropy SMAs can be realized by incorporating Hf additions.

The effect of heat input on weld-bead geometry, mechanical, phase transformation temperature, and corrosion properties of autogenous double pulse TIG welded nitinol sheets

This research aims to analyze the welding of 1 mm thick NiTinol sheets using an autogenous double pulse tungsten inert gas (DPTIG) welding process. The effect of heat input (HI) on bead geometry, microstructure, hardness, tensile strength, phase transformation temperature (PTT), and corrosion behavior was studied. The lower (111.25 J/mm), and higher (120.14 J/mm) HI produced an average grain size of 26 μm and 36 μm, respectively. The microstructure of the fusion zone (FZ) had coarser columnar grains with intermetallic phases such as Ni3Ti, and TiO2. The grain size in the FZ increased with the increase in HI. Sample P (111.25 J/mm) showed a higher hardness of 280.54 HV and tensile strength of 566 MPa due to a higher proportion of austenite phase (99.4%), the smaller grain size of 26 µm, a larger fraction of high angle grain boundary (HAGB) of 75.8%, and higher kernel average misorientation (KAM) value of 4.93. Compared to base metal (BM), sample P (111.25 J/mm), and sample S (120.14 J/mm) exhibited a reduction in tensile strength of 19.14% and 32.29%, respectively. The decline in hardness and tensile strength was attributed to the formation of intermetallic phases, a decrease in the Ti/Ni ratio, coarser grain formation, and a decrease in HAGB fraction and KAM values. The fractured tensile samples showed a mixed mode of fracture with dimples and cleavage facets. Compared to BM, Sample Q (118.05 J/mm) exhibited lesser variation in temperature hysteresis values for austenite and martensite temperatures, with a deviation of 0.4°C and 3.1°C, respectively. All the welded samples had better corrosion behavior than the BM due to a higher Ti/Ni ratio.