Search

General derivation of the well-known Ren–Otsuka relationship, 1 α d T o d x = − α β (where T o , x, α and β (> 0) are the transformation temperature and composition, as well as the composition and temperature coefficient of the critical shear constant, c′, respectively) for shape memory alloys, SMAs, is provided based on the similarity of interatomic potentials in the framework of dimensional analysis. A new dimensionless variable, t o x = T o x T m x , describing the phonon softening (where Tm is the melting point) is introduced. The dimensionless values of the heat of transformation, ΔH, and entropy, ΔS, as well as the elastic constants c′, c44, and A = c 44 c ′ are universal functions of to(x) and have the same constant values at to(0) within sub-classes of host SMAs having the same type of crystal symmetry change during martensitic transformation. The ratio of d t o d x and α has the same constant value for all members of a given sub-class, and relative increase in c′ with increasing composition should be compensated by the same decrease in to. In the generalized Ren–Otsuka relationship, the anisotropy factor A appears instead of c′, and α as well as β are the differences between the corresponding coefficients for the c44 and c′ elastic constants. The obtained linear relationship between h and to rationalizes the observed empirical linear relationships between the heat of transformation measured by differential scanning calorimetry (DSC) (QA⟶M) and the martensite start temperature, Ms. [ABSTRACT FROM AUTHOR]

The discovery of the Mg–Sc shape memory alloy system has become a milestone in the development of lightweight shape memory alloys. However, for the application scenarios with the highest demand at room temperature, the Mg–Sc alloy faces problems such as excessively low phase transition temperatures and poor room-temperature superelasticity, directly hindering the practical application of this new type of lightweight memory alloy. In this work, Mg–Sc based shape memory alloys with exceptional room temperature superelasticity have been screened for the first time utilizing Tm, phase transformation strain, and stress-strain curves. Co and Ge are selected as the most promising elements for improving Mg–Sc based alloys at room temperature. Furthermore, the mechanism behind the superelasticity of Mg–Sc alloy has been systematically unveiled and the average rate of energy change per unit time of the alloys was calculated for the first time. Co doped Mg–Sc based alloys exhibited the lowest variations in the average rate of energy change per unit time, Helmholtz free energy, and M1, along with a higher charge density between Co and Sc atoms. Additionally, a coupling effect between the d orbital of Co and Sc electrons and a lowered Fermi level was observed. These findings demonstrate that Co doping in Mg–Sc based alloys significantly reduces the superelastic hysteresis area and transformation driving force, and increases Tm and strain, thereby enhancing superelasticity. This research guides further studies and the design of new Mg–Sc based lightweight SMAs with outstanding superelasticity at room temperature.

In the present work, the effects of Nb addition and aging on the microstructure evolution and martensitic transformation of (Ni50.3Ti28.7Hf20.0Sc1.0)100-xNbx (x = 0, 5, 10, 15 at.%) high temperature shape memory alloys were investigated. The addition of Nb results in the formation of the eutectic β-Nb phase along with martensite and Sc2O3 at room temperature. Aging at 550 °C for 3 h leads to the formation of nanoscale H-phase. The surface area fraction of the H-phase decreases with increasing Nb content to 10 at.%. As the Nb content increases, the transformation temperatures of the solution-treated NiTiHfScNb alloy increase and then decrease due to the variation of Ni content in the matrix. The aged samples show a smaller transformation hysteresis in comparison with the solution-treated samples. The difference of thermal hysteresis between the solution-treated and the aged samples increases with increasing Nb content because of the H-phase precipitation and Nb solution in matrix.

The composite oxides of Ti and Zr can effectively induce acicular ferrite nucleation and refine austenite grain size. To study the transformation mechanism of acicular ferrite in Ti–Zr treated steel, the mass fraction of 0.038% titanium and 0.008% zirconium were added to low alloy steel by melting in a 25 kg vacuum induction furnace. The effect of austenitizing temperature on acicular ferrite transformation behavior was observed in-situ using a high-temperature laser confocal microscope: the samples were heated to 1250, 1300, 1350, and 1400 ℃ at a heating rate of 5 ℃·s−1 and then cooled to 400 ℃ at a cooling rate of 3 ℃·s−1 after holding for 300 s. The ferrite transformation behavior of samples during the above process was observed using a high-temperature confocal microscope. The inclusion composition of Ti–Zr treated steel and the nucleation of acicular ferrite on the inclusion surface were observed using a scanning electron microscope. The variation in microstructure at different austenitizing temperatures was observed using an optical microscope. The austenite grain size was found to increase from 125.6 to 279.8 μm with increasing austenitizing temperature from 1250 to 1400 ℃. The initial transformation temperature of acicular ferrite and side-plate ferrite increased, reached a maximum at 1350 ℃, and then decreased. The volume fraction of acicular ferrite increased from 39.6% to 83.6%. In Ti–Zr treated steel, the size of complex inclusion with Zr–Ti–O in core and Al–Ti–Zr–O in exterior and MnS precipitated on the surface was mainly concentrated in 1–3 μm. It could effectively promote acicular ferrite nucleation. The Mn-poor region and the good lattice relationship between complex inclusions and ferrite were the mechanisms by which the type of inclusions in the steel could promote acicular ferrite nucleation. Using classical nucleation theory, the nucleation potential of acicular ferrite under different conditions was calculated. The results showed that when the austenitizing temperature was 1300 ℃, the nucleation potential of acicular ferrite was the strongest, reaching 191.7 mm−2. The calculation results were consistent with the variated law of acicular ferrite volume fraction. An increase in austenite grain size led to a decrease in polygonal ferrite nucleation sites, an increase in acicular ferrite nucleation space, and the formation of many inclusions that effectively induced nucleation of acicular ferrite treated by titanium and zirconium, which increased the acicular ferrite volume fraction.

In the present study, the influence of the processing parameters on the transformation temperatures and microstructural evolution in a copper-based shape memory alloy was investigated. Five times remelting in identical conditions was conducted to investigate the effect of successive remelting on the microstructural and thermal behavior of the alloy. Samples were hot rolled up to 25, 50, 75, and 90% reduction in thickness after heating at 900 °C. It was demonstrated that one-time remelting is required to achieve a target alloy composition. Thermal hysteresis remained almost constant with elevation in the rolling strain imposed. Furthermore, increased rolling reduction led to decreased enthalpy and entropy levels. [ABSTRACT FROM AUTHOR]

SMAs can switch from one crystallographic structure to another in response to temperature or stress stimuli. When SMAs are exposed to mechanical cyclic stress, they can absorb and discharge mechanical energy by experiencing a reversible hysteretic shape change. SMAs are widely used for sensing, actuation, impact absorption, and vibration damping. This work studied the effect of CeO2 addition on the transformation temperature and wear resistance of Cu-Al-Ni SMAs. WhereCeO2 was added at different percent’s 0.5, 1, and 3 wt% to the base alloy, followed by casting and homogenization at 900oC. Some tests were carried out: Differential scanning calorimeter, Optical Microscope, Scanning Electron microscopy, Energy dispersion spectrometer, X-Ray Diffraction, and Wear and Hardness tests. OM and SEM tests reveal that both phases of martensite β and γ are found. Also, the additions of CeO2 show a visible effect on phase formation and transformation temperatures. It was observed that increasing of CeO2 particles in Cu-based SMAs owing to improve interfacial bonding between matrix and reinforcement and also observed that the variants become thicker with increasing in percent. Additions of different percentages of cerium oxide increase the hardness of Cu-Al-Ni SMAs. Due to the addition of CeO2 particles, the sample's wear rate decreases compared to pure SMAs.

The dissolution of carbides during the heating to the quenching temperature has a significant effect on the martensite oversaturation and the resulting mechanical properties. The kinetics of dissolution can be influenced by various external factors. This work deals with monitoring the carbide dissolution utilizing dilatometer analysis. The austenitization of 100CrMnSi6-4 bearing steel in two initial states was compared—after accelerated spheroidization annealing and conventional soft annealing. The main objective was to determine the amount of undissolved cementite during austenitization in the temperature range where only austenite and cementite are present in the structure. The austenitization temperature determines the degree of cementite dissolution and, consequently, the carbon content in austenite and thus the final properties after quenching. The cementite dissolution was quantified from dilatometric curves and image analysis. [ABSTRACT FROM AUTHOR]

Purpose: Nickel-titanium (nitinol) alloys possess a special set of properties that allow for a wide range of applications. Specifically, the transformation temperature for self-expanding nitinol peripheral stents allows for easy crimping at or below room temperature and reformation at body temperature becoming superelastic. Case Report: We report the case of an elderly man with iliac stenting 1 month prior, who presented several weeks after recovering from coronavirus disease 2019 with recurrent anterior-wall ST-elevation myocardial infarction. This was complicated by deformation and infolding of the previously implanted nitinol self-expanding stent in his right common iliac artery (CIA). Understanding nitinol's specific properties, we proceeded with rapid injections of iced saline to cool the nitinol stent to its transformation temperature while nudging the distal end of the stent with a partially inflated balloon. This maneuver softened the nitinol stent, allowing us to "unfold" and reappose it against the wall of the right CIA, resulting in successful restoration of the original shape of the nitinol self-expanding stent. Conclusion: This represents the first reported case describing treatment of an infolded nitinol self-expanding peripheral stent by exploiting the transformation temperature of nitinol using iced cold saline to successfully restore the stent's original shape and structure. [ABSTRACT FROM AUTHOR]

Machine learning approaches (ML) based on data-driven models are conducive to accelerating the assessments of the martensitic transformation peak temperature (Tp) of TiZrHfNiCoCu high entropy shape memory alloys (HESMAs) over a huge composition space. In this work, an interpretable machine learning workflow was established through dataset construction, feature selection, modeling and validation, and model interpretation. We identified a set of key feature combinations closely related to Tp, by exploiting Pearson correlation selection, univariate feature selection, and forward feature elimination. The established ML model was then used to estimate the Tp of three newly synthesized alloys, with their prediction relative errors of less than 3 % in comparison with the experimental measurements. The behaviors of our ML model were interpreted by the Shapley Additive exPlainations (SHAP) approach, demonstrating the crucial role of CV22 (Allred Rochow electronegativity) in the prediction of Tp. In addition, the ML model in combination with our designed interpretation strategy was further used to investigate the effects of alloying elements on the Tp, which showed that the TiZrHfNiCoCu HESMAs with 9 ≦ Co (mol%) ≤ 10 and 15 ≦ Cu (mol%) ≤ 17 have pronounced positive effects on Tp.

Ni47Ti44Nb9 alloys were successfully fabricated by laser powder bed fusion (LPBF) technique with different laser powers. The phase transformation behavior, tensile properties and shape memory response before and after heat treating were also investigated. The Ni47Ti44Nb9 LPBF alloys have good shaping properties, though a few defects were discovered. Phase transformation peaks did not appear in the as-built samples, but were observed in the heat-treated samples. The phase transformation temperatures of the heat-treated samples increase with the increase in laser power. The tension test at room temperature indicates that the LPBF samples exhibit poor tensile ductility, which may be related to the existence of pores and Ti2Ni or Ti4Ni2Ox phase during the LPBF process. However, the LPBF samples after heat treating still possess good shape memory effect (with recovery strain about 7.82–8%) and relatively high reverse transformation temperature (about 36–52.6 °C) when deformed to 8%. [ABSTRACT FROM AUTHOR]

The statistical-thermodynamic theory of ordering and electronic theory of ordering in the pseudo-potential approximation was used to study the influence of ternary addition of some transition metals on the atomic ordering behavior of Co0.5(Ti1–xMx)0.5 alloys with M = Fe, Pt, Re, V, Cr, Mn, Ni, Cu, Zn, Zr, Ag, Hf or Au up to a concentration of 1 at.%. The partial ordering energies, order-disorder phase transformation temperatures and partial short range order parameters have been calculated for these alloys. The analysis shows that the impurity elements in Co0.5(Ti1–xMx)0.5 alloys can be divided into two main groups on the basis of lattice site occupancy i.e. M = V, Cr, Mn, Cu, Zn, Zr, Ag, Hf and Au mainly substitute for Co sublattice sites whereas M = Fe, Ni, Pt or Re mainly substitute for Ti sublattice sites. Further, the order-disorder transformation temperatures were found to either increase or remain nearly unchanged by the addition of ternary impurities in the CoTi alloy depending on the absolute value of the partial ordering energies. Alloys of Ti with V, Cr, Mn, Cu, Zn, Zr, Ag, Hf or Au in place of Co and alloys of Co with Fe, Ni, Pt or Re in place of Ti can be predicted for future. The results of the present analysis are in good agreement with the available experimental data on these alloys.

The transformation of gibbsite to α-alumina occurs in the range 1100 to 1300°C. The higher the calcination temperature, the larger the crystallites and this leads to abnormal grain growth. The main goal of this research was to reduce the transformation temperature of gibbsite to α-alumina by reducing the gibbsite particles size. The sodium content of the gibbsite used in the study was reduced to less than 0.1% by washing it in HCl solution. It was then ground in a fast mill at ambient conditions for different times then calcined at different temperatures. The microstructure, particles size and thermal behaviour of the samples were examined with SEM, XRD, XRF, PSA and STA, respectively. In a sample ground for 180 min, the transformation temperature decreased from about 1300°C to 1150°C. The reduction in the calcination temperature led to a reduction in α-alumina crystallite size from about 77.16 nm to 64.37 nm. [ABSTRACT FROM AUTHOR]

Although Ni-rich 60 NiTi shape memory alloy (SMA) shows superior properties, it is difficult to process due to its high hardness and studies on the manufacturing method are still needed. By the hot isostatic pressing process (HIP), parts close to the net shape are produced and the second operation may no longer be required. In this study, the effects of mechanical alloying on NiTi alloy produced by the HIP process were investigated. The starting powders of the first group were mechanically alloyed. The starting powders of the second group were mechanically mixed. Afterwards, the microstructures, transformation temperatures and some mechanical properties of these two groups were compared. For these examinations, SEM-EDS, XRD, DSC analyzes and microhardness measurement, density measurement by hydrostatic weighing method were performed. The result showed, mechanical alloying causes a more homogeneous microstructure and higher transformation temperatures. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) was used to manufacture smart programmed structures with customized properties made of biocompatible NiTi shape-memory alloy. A series of helixes was produced with systematically varied SLM process parameters Laser Exposure Time and Laser Power in order to specifically change the thermo-mechanical material properties of the 3D-structures. This innovation opens up the possibility to adjust the NiTi phase transformation temperature during the manufacturing process. This controllable property determines which of the two crystallographic phases martensite or austenite is present at a certain operating temperature and allows the mechanical properties to be adjusted: martensitic devices are soft and pseudo-plastic due to the shape-memory effect, whereas austenitic structures are pseudo-elastic. In a further step, the SLM process parameters were locally varied within 4Dprinted twin-helixes. As a result, the phases, respectively the mechanical properties of a single component were adjusted at different locations. The ratio of elastic to plastic deformation and the spring constant of the helix can be locally controlled. This allows, for example, the spatio-temporal programming of 3D-printed surgical instruments or implants that are stimuliresponsive.

The shape memory thin films are most suitable candidates as actuators in MEMS applications than other smart materials due to its ability to produce larger recovery strains at low operation voltages. Recently, Ti based shape memory alloys are gaining attention due to its ability to produce stable shape memory properties at high temperatures. In current study, Ti-Zr-Mo high-temperature shape memory thin films were fabricated using multi-target DC/RF magnetron sputtering system on Si (100) substrate. Deposition time and target power were varied to obtain the desired composition. Post-annealing was carried out at 500 °C, 600 °C and 700 °C for 15 min each to crystallize the thin films that were amorphous in the homogenized condition. The annealing temperature was varied to observe the structural and morphological changes. The total thickness of the film was found to be around 300 nm measured from the cross-sectional micrographs. The results suggest that flatness of surface topography is attributed to higher ad-atom mobility with increasing the annealing temperature. The martensite phase (α’) was observed after annealing at 500 °C and the formation of silicides was observed with annealing at higher temperatures. The transformation temperature of 220 °C was obtained from electrical resistivity measurement. The enhanced mechanical properties with maintaining structural stability was observed in Ti-Zr-Mo thin film annealed at 500 °C for 15 min.

Tuning the martensite transformation temperature through composition design has become an important way to broaden the applicable temperature range of shape memory alloys (SMAs). The empirical formula based on traditional statistics is a key reference for composition design. Due to the lack of experimental data, a large deviation may exist among the prediction results from the empirical formulas obtained by different data sources. In present work, we proposed an augmentation strategy of empirical formula based on a machine learning method to build the relationship between martensite transformation start temperature (Ms) and compositions in Cu-Al-based SMA system. A series of ML models were established by physical and chemical features and a Gaussian radial basis kernel function support vector machine (SVR.rbf) model was screened out based on mathematical and domain knowledge criteria. An augmented empirical formula of Ms as the function of compositions was fitted based on the abundant augmented dataset combined experimental data with predicted data by the SVR.rbf model. Compared with previous empirical formula fitted by small experimental dataset, the accuracy and robustness of the augmented empirical formula was significantly improved without additional experimental cost. This strategy offers a recipe to build empirical formula based on a small experimental dataset.

Ni47Ti44Nb9 alloys were successfully fabricated by laser powder bed fusion (LPBF) technique with different laser powers. The phase transformation behavior, tensile properties and shape memory response before and after heat treating were also investigated. The Ni47Ti44Nb9 LPBF alloys have good shaping properties, though a few defects were discovered. Phase transformation peaks did not appear in the as-built samples, but were observed in the heat-treated samples. The phase transformation temperatures of the heat-treated samples increase with the increase in laser power. The tension test at room temperature indicates that the LPBF samples exhibit poor tensile ductility, which may be related to the existence of pores and Ti2Ni or Ti4Ni2Ox phase during the LPBF process. However, the LPBF samples after heat treating still possess good shape memory effect (with recovery strain about 7.82–8%) and relatively high reverse transformation temperature (about 36–52.6 °C) when deformed to 8%.

Recently, researchers have shown an increased interest in Cu-based shape memory alloys due to their special characteristics, which can be used in high-temperature applications. In this study, ternary shape memory alloys in the form of CuAlFe with different ratios of iron and quaternary CuAlFe alloys containing Ni, Mn, and Ti were produced by arc melting. Then the produced alloys were kept at 900 °C for 24 hours to make sure that all constituents in the alloys were homogeneously distributed. The change in the transformation temperatures for all samples was checked out by Differential Scanning Calorimetry (DSC). Also, the change in the crystal structure and microstructure were determined by x-ray diffractometer (XRD) and scanning electron microscopy (SEM), respectively. The aim of this study is to compare the thermal and microstructural properties of quaternary alloys formed by adding Ni, Mn, and Ti elements to CuAlFe-based shape memory alloy with different rates, which is not available in the literature. The result of this study; although the electron concentration value increased, a significant decrease was observed in the values of the transformation temperatures. Increasing Fe-element decreased the transformation temperature non-linearly. Ni and Mn contents added to CuAlFe shape memory alloys have reduced transformation temperatures, such as Af and Mf. The XRD and SEM-EDX measurements showed the martensite phase with some produced compound precipitated in the matrix phase. [ABSTRACT FROM AUTHOR]

The effect of Zr and Cu additions on the phase stability, microstructure and martensitic transformation temperature of binary NiTi alloys has been investigated with a combined approach of experimental measurements and first principle density functional theory calculations. In this work, multilayer Ni/Ti/Zr/Cu films have been deposited using the magnetron sputtering on Si substrates at room temperature and subsequently annealed at 350 °C for complete inter-diffusion of multilayers to create amorphous phase followed by high temperature annealing at 600 °C for 5 min to achieve Ni44Ti35Zr15Cu6 shape memory alloys. The high temperature annealing is required for the formation of crystalline phases. The x-ray diffraction pattern of the film annealed at 600 °C indicated the presence of martensite phase. The surface and interface studies were performed focusing on morphology and interlayer diffusion over the nano-level structure at 600 °C. The elemental mapping showed near-uniform distribution of constituent elements after annealing. Atomic force microscopy results showed the increase in surface roughness at annealing temperature of 600 °C due to grain growth. The formation energy results indicate that the Zr and Cu additions to NiTi favor the formation of monoclinic B19' phase. The differential scanning calorimetry results show that the martensitic transformation temperature increases with Zr and Cu additions. Nanoindentation studies for Ni44Ti35Zr15Cu6 films showed an increase in depth recovery for the crystalline film. A theoretical model has been used, to determine the hysteresis of shape memory alloys as predicted by the geometric nonlinear theory of martensite. [ABSTRACT FROM AUTHOR]

The statistical-thermodynamic theory of ordering and electronic theory of ordering in the pseudo-potential approximation was used to study the influence of ternary addition of some transition metals on the atomic ordering behavior of Co0.5(Ti1-xMx)0.5 alloys with M = Fe, Pt, Re, V, Cr, Mn, Ni, Cu, Zn, Zr, Ag, Hf or Au up to a concentration of 1 at.%. The partial ordering energies, order-disorder phase transformation temperatures and partial short range order parameters have been calculated for these alloys. The analysis shows that the impurity elements in Co0.5(Ti1-xMx)0.5 alloys can be divided into two main groups on the basis of lattice site occupancy i.e. M = V, Cr, Mn, Cu, Zn, Zr, Ag, Hf and Au mainly substitute for Co sublattice sites whereas M = Fe, Ni, Pt or Re mainly substitute for Ti sublattice sites. Further, the order-disorder transformation temperatures were found to either increase or remain nearly unchanged by the addition of ternary impurities in the CoTi alloy depending on the absolute value of the partial ordering energies. Alloys of Ti with V, Cr, Mn, Cu, Zn, Zr, Ag, Hf or Au in place of Co and alloys of Co with Fe, Ni, Pt or Re in place of Ti can be predicted for future. The results of the present analysis are in good agreement with the available experimental data on these alloys. [ABSTRACT FROM AUTHOR]

The ferrite–bainite microstructures and mechanical properties in a hot-rolled dual phase steel with different transformation temperatures were investigated in this paper. The deformation behavior of bainite and ferrite was analyzed by using in situ scanning electron microscope. The results showed that the ferrite and bainite can be refined and the volume fraction of bainite can be slightly increased by 5% by decreasing the ferrite transformation temperature from 690 to 635 °C and increasing the bainite transformation temperature from 400 to 450 °C. The strengthening mechanism was dislocation difference in polygonal and acicular ferrite and then the grain size difference of ferrite. The hole expansion ratio increased from 52.9 to 83.7% with the ferrite transformation temperature decreasing. The cracks or voids were smaller in size and also the number in steel with the lower ferrite transformation temperature after expanding. The microstructure separation along the boundary between bainite and ferrite and the slip band in the ferrite appeared at the non-uniform deformation stage. However, fewer appeared in the microstructure of steel with lower ferrite transformation temperature. Cooperative deformation of ferrite and bainite and finer microstructure in steel with lower ferrite transformation temperature were the mechanisms why the cracks could not easily nucleated and propagated, respectively. Thus this was also why there was a better hole expansion ratio. The ferrite–bainite microstructures and mechanical properties in a hot-rolled dual phase steel with different transformation temperatures were investigated. The deformation behavior of bainite and ferrite was analyzed by using in situ scanning electron microscope. The strengthening mechanism was dislocation difference in polygonal and acicular ferrite and then the grain size difference of ferrite. The hole expansion ratio increased from 52.9 to 83.7%. Cooperative deformation of ferrite and bainite and finer microstructure in steel with lower ferrite transformation temperature were the mechanisms why the cracks could not easily nucleated and propagated, respectively. Thus this was also why there was a better hole expansion ratio. [ABSTRACT FROM AUTHOR]

The transformation temperatures, magnetization behavior, shape memory behavior, and mechanical properties of polycrystalline Ni45Mn40Co5Sb10−xBx (at.%) (x = 0, 1, 2, 3, 4, 5) alloys were systematically investigated. It was revealed that substituting Sb with B drastically increases the transformation temperatures, while it decreases the saturation magnetization due to the alteration of electron concentration of the matrix and formation of Co-rich second phases. With the substitution of Sb with 5% B, martensite start temperature and activation energy were increased from 50 to 316.8 °C, and 185 to 722.6 kJ mol−1, respectively. The thermal cycling under stress, superelasticity, and failure experiments showed that shape memory properties and strength were improved by the substitution of Sb with B. The shape memory effect with maximum recoverable strain of 1.6% was observed with in Ni45Mn40Co5Sb9B1, and perfect superelasticity was exhibited at 220 °C in Ni45Mn40Co5Sb8B2. It was concluded that NiMnCoSb alloys can be used as high-temperature magnetic shape memory alloys as they exhibit transformation temperatures above 100 °C and show promising shape memory and superelasticity behavior, and there is a magnetization difference between their transforming phases. [ABSTRACT FROM AUTHOR]

The memory effect of shape-memory alloys (SMAs) has opened interesting perspectives to create prestress states in concrete elements. However, the procedure has not been yet fully resolved due to the complex thermomechanical behavior of these alloys, in addition to the practical difficulties of mechanical coupling between SMA and concrete elements. The present study deals with tests on the development of prestressing forces in concrete beams during the thermal cycle required in the procedure. Pre-stretched nickel–titanium wires were externally placed on concrete prismatic beams equipped with strain gauges. As concrete rupture may occur during the heating by the Joule effect, a compromise must be found between the SMA pre-stretch level and the maximum temperature to be applied before returning to ambient temperature. A macroscopic model was developed to analyze this compromise. The complex thermomechanical response of SMAs implies a particular attention in the definition of the ambient temperature and heating conditions for the creation of prestress states in concrete components. [ABSTRACT FROM AUTHOR]

Accurately predicting the metastable zone width is beneficial for controlling the cooling crystallization to increase particle size. In this work, the transformation temperature between anhydrous inositol and dihydrate inositol was determined to be 301.2 K. In industry, only stable anhydrous inositol is required, so the metastable zone width was measured in the temperature range from 308.2 K to 353.2 K. A novel prediction model for metastable zone width was proposed. Cooling rate, stirring linear velocity, saturation temperature and transformation temperature were considered. Fitted with sufficient data, three predictive equations used for different temperature ranges were obtained. The experimental values were in good agreement with the predictive values. Under the guidance of the prediction equations, the particle size and flowability of the obtained anhydrous inositol significantly increased. The results provide guidance for the preparation of large particle inositol and provide reference for the prediction of metastable zone width in other systems. [Display omitted] • The influence of transformation temperature on the MSZW of MI was revealed. • A novel prediction model of MSZW based on Sangwal's self-consistent model was proposed. • The parameters of industrial crystallization are considered in the prediction model. • The prediction model is suitable for both batch and continuous crystallization • The powder flowability of inositol was improved. [ABSTRACT FROM AUTHOR]

Copper based shape memory materials was interesting group of metal alloys that have a widespread potential in medical and industrial application due to their characteristics ,the possibility of exhibiting shape memory behavior and lower cost. In this research the alloy (Cu-(15-40) wt%Zn-6wt.%Al) has been prepared by powder metallurgy technique Zn element (15, 20, 25, 30, 35, 40 wt%Zn) and fixed percentage of Al content which is 6.wt%Al then aluminum replaced by (Si, Sn, Ni )element at fixed percentage of 6wt.%, in order to study the effect of these elements on SMA. After samples preparation examination were done by using XRD, SEM technique, DSC, Vickers hardness, Archimedes method to measure the porosity percentage and corrosion rate in different solutions (HCl, NaOH and SEAWATER).The XRD and microstructure results show that all samples with and without additives consist of two phases (β-phase) and (α-phase) at room temperature and the addition of alloying elements in these percentages does not have effect on present phases. the hardness increased with zinc content because the formation of intermetallic compound of CuZn that responsible to hardness while The addition of Si ,Sn and Ni leads to lower the hardness than aluminum. The bulk density increased with the alloys without addition alloying elements(Si, Ni and Sn ) while apparent porosity decreased with it the reason for this phenomenon due to the characterization of alloying elements that addition to the alloy. From the results of corrosion test can be show the alloy with 35wt% Zn have the higher corrosion resistance in all media (HCl, NaOH and sea water) and the addition of alloying element lead to improve the corrosion resistance. Finally, it is observed that the Copper base shape memory alloys with these types of additives are suitable for use in different application.

In this study, some physical properties of a quaternary Cu-based alloy have been studied on the example of the alloy Cu–13Al–4.5Ni–1.5Ti (wt %) that was produced by using the arc-melting method. Four specimens were made from the alloy ingot, and three of them were subjected to heat treatment at 930°C for 30 min. Later, they were separately quenched into liquid nitrogen (–196°C), alcohol (0°C), and iced-brine (6°C) mediums. Differential Scanning Calorimetry (DSC) measurements of all samples were performed to determine the effect of quenching on the phase transformation temperatures. It was observed that the quaternary Cu–Al–Ni–Ti alloy is a high temperature shape memory alloy (HTSMA) and its transformation temperatures significantly were affected by heat treatments, e.g., the phase transformation temperatures increased via quenching in alcohol and iced brine by approximately 100 K. Moreover, optical microscopy (OM) and Scanning Electron Microscopy (SEM) images were taken to observe the changes in the microstructure after heat treatment. It was revealed that grain boundaries were more discernable in the samples that were quenched in alcohol and iced brine, also the volume fraction of martensite plates was increased. Crystal structures of samples at room temperature were determined by using X-ray diffractograms, whereby, the pattern showed the presence of β', γ2, and X phases, which are of martensite origin. [ABSTRACT FROM AUTHOR]

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

A key property for the design of new shape memory alloys is their working temperature range that depends on their transformation temperature T0. In previous works, T0 was predicted using a simple linear regression with respect to the energy difference between the parent and the martensitic phases, Δ E p − m . In this paper, we developed an accurate method to predict T0 based on machine learning assisted by the first-principles calculations. First-principles calculations were performed on 15 shape memory alloys; then, we proposed an artificial neural network method that used not only computed Δ E p − m but also bulk moduli as input variables to predict T0. The prediction error of T0 was improved to 49 K for the proposed artificial neural network compared with 188 K for simple linear regression. [ABSTRACT FROM AUTHOR]

Ti‒50.13Ni and Ti‒49.62Ni (at.%) shape memory alloy ribbons were fabricated by melt-spinning method at different circumferential wheel velocities. The effects of wheel velocity, chemical composition and heat treatments on microstructure and Transformation temperature were investigated. Differences in wheel velocity led to differences in cooling rate and sample dimension, as well as in phase transformation temperatures. Two heat treatment conditions were studied, 350°C for 1h and 350°C for 5h. In the samples produced at high wheel velocity and heat-treated at 350°C for 5h, nanosized Ti-rich precipitates were observed in both chemical compositions. Cross-sectional microstructure was studied by optical microscopy; SEM was used to study the nanometric grains and nano precipitation. The transformation temperatures were analyzed by DSC.

The present communication reports the production of Cu81-Al13-Ni4-Ti2 shape memory alloy (SMA) by an arcmelting method. A piece of this alloy is subjected to heat treatment at 930°C for 30 min and then shock-cooled in liquid nitrogen (-196°C), alcohol (0°C) and saline ice water (+6°C). Differential Scanning Calorimetry (DSC) is performed on samples with no heat treatment and on those subjected to three different heat treatments. It is found that the chosen heat treatments increase significantly the phase transformation temperatures of the shape memory alloy. Some changes in the microstructure of the alloy are also observed after the heat treatment. The grain boundaries become more pronounced, while the martensite plates increase in the samples which are shock-cooled in alcohol and saline ice water. The crystalline structures of the samples are investigated at room temperature. The XRD diffractograms reveal that bı phase (martensite phases) increases in the alloys subjected to heat treatment. [ABSTRACT FROM AUTHOR]

Full penetration friction stir welding was conducted on 12 mm thick reduced activation ferritic-martensitic steel at tool rotational speeds of 500 and 900 rev min−1. Comparator welds at 500 rev min−1 were also produced in 6 mm thick reduced activation ferritic-martensitic steel plate to evaluate section thickness effects. Increase in section thickness led to an increase in heat input, which strongly influenced the microstructure evolution in stir zone (SZ), thermo-mechanical affected zone and the overall hardness in the SZ of this steel. In the as-welded condition, the base metal microstructure was significantly altered and resulted in carbide-free grain boundaries. The desirable microstructure and mechanical properties were achieved by subjecting the as-welded joints to appropriate post-weld heat treatments. [ABSTRACT FROM AUTHOR]

Abstract: The results of calorimetric studies of a histological preparation of a surgically excised Baker's cyst are presented. The measurements were performed on a DSC 204 F1 Phoenix differential scanning calorimeter (Netzsch, Germany). The measurement error of the temperature dependences of the specific heat capacity of the samples analyzed did not exceed 2%. The denaturation temperature, which corresponded to the peak of the thermal signal, was 68.1°C for Baker's cyst tissues and the denaturation enthalpy was 4.352 J/g. No thermal effects were observed on the thermograms when the samples were re-scanned; this is indicative of irreversible changes related to complete denaturation of collagen in the samples. [ABSTRACT FROM AUTHOR]

The possibility of diffusionless phase transformations in the surface layer of the ground part under the influence of instantaneous grinding temperature is investigated and analyzed. This is important because the phase Feα-Feγ transformations that may occur when grinding parts lead to the appearance of so-called grinding burns, which 2-3 times reduce the reliability and durability of the part in the working mechanism. The mechanism of phase transformations, the critical temperature of these transformations and the associated processing modes that provide this temperature are determined. This allows a reasonable approach to the definition of grinding modes and, if necessary, the application of the cooling method. In addition, the problem of optimizing grinding regimes can be solved if the processing performance is taken as a target function, and grinding temperature as a limitation. With rapid surface heating of the hardened steel part by the grinding temperature above the Ac1 line, there is a reverse martensitic transformation Feα→Feγ. The martensite range during cooling Mn-Mk to a large extent covers negative temperatures. Therefore, austenite is partially fixed in the surface layer, forming a so-called quenching burn. Dependences for determining the formation temperature for steel of any chemical composition, give the possibility to maintain the value of grinding temperature below this level during grinding. The mechanism of diffusionless reverse martensitic transformation in the high-speed surface heating by cutting grains (instantaneous temperature) is considered. The heating rate and the effect of the pressure produced by the abrasive grain on the metal during the chip removal are experimentally determined. Thus, the possibility of diffusionless phase transformation is substantiated and the dependences for the calculation of austenite formation temperatures are given, which in turn provides the opportunity to calculate safe processing regimes. [ABSTRACT FROM AUTHOR]