Martensitic Phase Transformation Temperature Research Articles

Tuning the thermal cyclic stability of martensitic transformation in Ni50.3Ti29.7Hf20 high temperature shape memory alloy

Thermal stimulus-responsive NiTi-based shape memory alloys, which undergo reversible, diffusion-less martensitic phase transformation, have emerged as important functional materials. Amongst them, Ni-rich NiTiHf high temperature shape memory alloys exhibit martensitic phase transformation temperatures well above 100 °C, making them suitable for high temperature applications. However, during repeated thermal cycles their transformation temperatures show instabilities which limit their practical applications. Here, we perform thermal cycling experiments at fixed as well as variable heating/cooling rates on the Ni50.3Ti29.7Hf20 alloy which is heat-treated at different temperatures. We successfully minimized the variations in phase transformation temperatures to an acceptable range by aging the alloy below 500 °C for 3 h. We further show that this minimization correlates well with high activation energy required for the phase transformation elucidating the physical reason behind this observation. Our results pave the way forward for designing Ni-rich NiTiHf shape memory alloys with a stable functional response.

Effect of Hf solute addition on the phase transformation behavior and hardness of a Ni-rich NiTi alloy

Hf substituted NiTi alloys are crucial for high temperature shape memory applications owing to their martensitic phase transformation temperatures around 100°C. For further high temperature applications above this limit, a balanced combination of high phase transformation temperatures, high strength and low thermal hysteresis is the foremost criterion. Here, we show that substitution of an array of Hf concentrations (5–25 at.%) to Ni50.3Ti49.7 alloy leads to a wide range of phase transformation temperatures from sub-zero to 280°C. Our studies establish complete solid solution solubility of Hf in the Ni50.3Ti49.7 alloy up to 25 at.% Hf. As a result, the hardness Ni50.3Ti49.7 alloy increases linearly with Hf concentration on account of solid solution strengthening effect. We further show that the Ni50.3Ti29.7Hf20 alloy exhibits least thermal hysteresis combined with high phase transformation temperatures and hardness amongst the compositions investigated. Our study paves the way for designing Ni-rich NiTiHf high temperature shape memory alloys, with operating temperatures up to 250°C and thermal hysteresis as low as 30°C.

Modeling of Martensite Transformation in White Layer under Thermo-mechanical Coupling in Hard-Cutting Process

Martensite volume fraction determines the hardness and wear resistance of workpiece, predicting the martensite volume fraction of the white layer is of great significance for improving the surface quality of the workpiece. Accordingly, a theoretical model on the martensite volume fraction was developed in combination with the martensite transformation temperature model and the hard-cutting FE model. A finite element (FE) model of the hard-cutting was established to obtain the stress distribution of the workpieces. A calculation model of martensite phase transformation temperature $$M_{\text{S}}$$ under the influence of the cooling rate and stress was deduced based on the change of Gibbs free energy. A theoretical model of martensite volume fraction $$f_{\text{M}}$$ of the white layer was developed based on the $$M_{\text{S}}$$ and the FE simulations. The $$f_{\text{M}}$$ calculated by the theoretical model is in accordance with the experimental result. The effects of cutting speed, feed rate, flank wear and tool rake angle on the $$f_{\text{M}}$$ in the white layers were predicted and analyzed; the results show that the $$f_{\text{M}}$$ decreases first and then increases with the cutting speed, decreases with the feed rate and the flank wear, and increases with the tool rake angle.

Influence of Cr Alloying (1.5 to 5 at.%) on Martensitic Phase Transformation Temperatures in Co-Ni-Ga-Cr Thin Films

A Co-Ni-Ga-Cr thin film materials library with a Cr concentration gradient ranging from 1.5 at.% to 5 at.% was magnetron-sputtered to determine the influence of Cr additions on the martensite transformation temperature of non-stoichiometric Co2NiGa-based Heusler alloys. An increase of the phase transformation temperature from 30 °C for 5 at.% Cr up to 100 °C for 1.5 at.% Cr was determined by a peak fitting analysis of temperature-dependent X-ray diffraction data.

Bipolar resistive switching behavior in MoS2 nanosheets fabricated on ferromagnetic shape memory alloy

The present study explores the systematic investigation of resistive switching response of magnetron sputtered MoS2 thin films sandwiched between a Ni-Mn-In ferromagnetic shape memory alloy (bottom) and copper (top) electrodes. The Cu/MoS2/Ni-Mn-In device exhibits stable and reproducible bipolar resistive switching behavior. The current-voltage (I-V) analysis suggests that the device shows ohmic conduction behavior in the low resistance state (LRS) while space charge limited conduction is the dominating conduction mechanism in the high resistance state (HRS). The compliance current vs reset current measurements were also performed which reveals that the power consumption of the device can be suppressed by decreasing the compliance current. To explain the resistive switching behavior in the Cu/MoS2/Ni-Mn-In device, a conceptual model based on copper ion migration, is proposed and well explained. The resistive switching parameters such as the set voltage, LRS and HRS resistances, are also investigated in a temperature range overlapping with the martensite phase transformation temperatures of the bottom ferromagnetic shape memory alloy (Ni-Mn-In) electrode. It provides temperature as an extra degree of freedom to modulate the resistive switching characteristics of the fabricated device. The Cu/MoS2/Ni-Mn-In device shows a decent endurance of 500 and a long retention of 103. These results demonstrate the feasibility of the MoS2 based devices for futuristic tunable nonvolatile resistive random access memory applications.

Atomistic simulation of shape memory effect (SME) and superelasticity (SE) in nano-porous NiTi shape memory alloy (SMA)

Porosity can play an important role in altering the phase transformation characteristics of NiTi shape memory alloys (SMA), thus changing its shape memory as well as its superelasticity properties. This work, based on atomistic simulations of binary NiTi SMA, documents the effects of porosity at the nanometer length scale on phase fraction evolution kinetics, transformation temperatures, and stress-strain response. Classical molecular dynamics simulations are performed using a well-examined and verified Finnis-Sinclair type embedded-atom method interatomic potential. Simulation results for the nano-porous NiTi with various porosity configurations are compared to non-porous NiTi. The martensite phase fraction and transformation temperatures increase noticeably with increasing porosity, and the stress-strain response shows noticeable variation with porosity. The residual strain and hysteretic energy dissipation capacity increase significantly with increasing porosity.

Residual stresses of LTT welds in large-scale components

Residual stresses of welds become more and more important influencing cold cracking as well as the fatigue life of welded components. Low transformation temperature (LTT) filler materials offer the opportunity to alter the residual stresses already during the welding process by means of adjusted martensite phase transformation temperature (M S). In the current paper, welding residual stresses are studied putting the focus on M S while joining heavy steel sections with a thickness of 20 and 25 mm, respectively. The residual stress state was determined at the top surface using X-ray diffraction as well as in the bulk by neutron diffraction. The results compare the residual stresses present in a conventional weld and LTT welds when multi-pass welding of large-scale components was applied. Repeated phase transformation in the case of the LTT weld is more vital for the residual stresses present in the real-life-like joints. This accounts for the top surface in longitudinal direction but is most pronounced for the bulk of the welds. Detrimental tensile residual stresses are mainly reduced in the bulk in comparison to a conventional filler wire even in multi-pass welds of thick steel sections.

The effect of addition of various elements on properties of NiTi-based shape memory alloys for biomedical application

In biomedical applications, NiTi and NiTi-based alloys that show their shape memory effects at body temperature are preferred. In this study, the purpose is to produce NiTi and NiTi-based alloys with various chemical rates and electron concentrations and to examine their various physical properties. N45Ti55, Ni45Ti50Cr2.5Cu2.5, Ni48Ti51X (X=Mn, Sn, Co) alloys were produced in an arc melter furnace in this study. After the homogenization of these alloys, the martensitic phase transformation temperatures were determined with differential-scanner calorimeter. The transformation temperature was found to be below the 37 ° C (body temperature) in Ni45Ti50Cr2.5Cu2.5, Ni48Ti51X (X=Mn, Co) alloys; and the transformation temperature of the N45Ti55, Ni48Ti51Sn alloys was found to be over 37 ° C . Then, the micro and crystal structure analyses of the alloys were made, and it was determined that Ni45Ti50Cr2.5Cu2.5, Ni48Ti51X (X=Mn, Co) alloys, which were in austenite phase at room temperature, included B2 (NiTi) phase and Ti2Ni precipitation phase, and the alloys that were in the martensite phase at room temperature included B19i (NiTi) phase and Ti2Ni phase. The common phase in both alloy groups is the Ti2Ni phase, and this type of phase is generally seen in NiTi alloys that are rich in titanium (Ti-rich).

Martensitic transformation and microstructure of dual-phase Ti44Ni47Nb9 shape memory alloy after high-velocity impact

Martensitic transformation, microstructure and mechanical properties of a Ti44Ni47Nb9 alloy under a high-velocity impact at 1.0km·s−1 were studied. The deformation mechanism was also discussed based on the Johnson–Cook (J–C) material model. The results showed that the transformation behavior, microstructure and mechanical properties along the impact direction of the impacted specimen exhibit regionalization characteristics. Martensite and reverse phase transformation temperature decreased and stabilized during three thermal cycles. Stress-induced martensite plates emerged in the matrix, and high-density dislocations were introduced into the matrix, β-Nb particles and their interface with the highest dislocation density at the interface. The deformation recovery tends to first increase and then decrease gradually with increasing distance from the crater.

Development of an interatomic potential for the simulation of defects, plasticity, and phase transformations in titanium.

New interatomic potentials describing defects, plasticity, and high temperature phase transitions for Ti are presented. Fitting the martensitic hcp-bcc phase transformation temperature requires an efficient and accurate method to determine it. We apply a molecular dynamics method based on determination of the melting temperature of competing solid phases, and Gibbs-Helmholtz integration, and a lattice-switch Monte Carlo method: these agree on the hcp-bcc transformation temperatures to within 2 K. We were able to develop embedded atom potentials which give a good fit to either low or high temperature data, but not both. The first developed potential (Ti1) reproduces the hcp-bcc transformation and melting temperatures and is suitable for the simulation of phase transitions and bcc Ti. Two other potentials (Ti2 and Ti3) correctly describe defect properties and can be used to simulate plasticity or radiation damage in hcp Ti. The fact that a single embedded atom method potential cannot describe both low and high temperature phases may be attributed to neglect of electronic degrees of freedom, notably bcc has a much higher electronic entropy. A temperature-dependent potential obtained from the combination of potentials Ti1 and Ti2 may be used to simulate Ti properties at any temperature.

Shape Memory Behaviour of NiTi Alloy Produced by MIM Using Palm Stearin Based Binder

In this present work, NiTi alloy has been successfully produced by metal injection moulding (MIM) starting with elemental powders mixture of Nickel (Ni) and Titanium (Ti) mixed with a composite binder of palm stearin (PS) and polyethylene (PE). Two different atomic fractions of Ni-Ti were investigated; 50-50 and 50.8-49.2 and the powder loading used was 65.5vol%. The green parts were successfully injection moulded at an optimum temperature of 130°C. The samples were then underwent solvent extraction using n-heptane solution to remove the primary binder of PS. It was followed by thermal debinding to completely remove the backbone binder of PE and subsequently sintered in high vacuum at 1050°C to allow diffusion of the elemental Ni and Ti powders to form NiTi alloy. The phase constituents of the sintered specimens were characterized by X-Ray Diffraction (XRD) and by Scanning Electron Microscopy (SEM), equipped with EDX analysis under back-scattered electron (BSE) mode. The reversible austenite to martensite phase transformation temperatures (PTTs) correspond to shape memory effect (SME) was determined by Differential Scanning Calorimeter (DSC) with heating and cooling cycle in the range of-50 and 200°C. The influence of Ni-Ti ratio and the processing conditions on phase constituents and SME was then analyzed and discussed.

THE INFLUENCE OF NI-TI RATIO ON THE REVERSIBLE AUSTENITE-MARTENSITE TRANSFORMATION AND MECHANICAL PROPERTIES PRODUCED BY METAL INJECTION MOULDING

This paper highlights the influence of Ni-Ti ratio on the phase constituents, the reversible austenite-martensite transformation and mechanical properties produced by metal injection molding (MIM). The binder system used was mainly palm stearin with minor fraction of polyethylene. Injection moulding was done successfully at 130˚C to form tensile shape samples. It was followed by solvent extraction, thermal debinding at 500oC and subsequently sintered in high vacuum at 1100˚C. The result showed that as the Ni content increased, the fraction of austenite phase also increased owing to greater fraction of transient liquid phase formation during the sintering, thus improved the mechanical tensile properties. However, the reversible austenite to martensite phase transformation temperatures (PTTs) seemed to be broadened with increased Ni content due to formation of metastable R-phase.

Elevated Temperature, In Situ Micromechanical Characterization of a High Temperature Ternary Shape Memory Alloy

The microthermomechanical behavior of a precipitation-hardenable Ni-48Ti-25Pd (at.%) shape memory alloy has been investigated as a function of temperature. Micropillars were fabricated within a large 〈145〉-oriented grain and compressed in situ in the SEM at elevated temperatures corresponding to the martensite and austenite phase transformation temperatures. The precipitation-strengthened alloys exhibited stable pseudoelastic behavior with little or no residual strains when near the transformation temperatures. In the plastic regime, slip was observed to occur via pencil glide, circumventing the fine scale precipitates along multiple slip planes.

A low temperature in-situ crystalline TiNi shape memory thin film deposited by magnetron sputtering

ABSTRACT TiNi films deposited by magnetron sputtering usually have amorphous structure and must be annealed at high temperature to obtain crystallization. We have synthesized an in-situ fully crystalline TiNi shape memory thin film at low temperature by dc magnetron sputtering. Application of pulsed direct current to the substrate is effective to obtain a crystalline TiNi film. Nine different conditions were used for deposition in silicon wafer and thin copper plate substrates. Structural properties and phase transformation temperatures of the TiNi films were investigated. To examine the structural properties of the films, XRD, SEM and EDS techniques were used. Austenitic and martensitic phase transformation temperatures were observed via DSC (differential scanning calorimeter) tests. TiNi (110) B2 austenite peaks were observed in the Run7 film. The crystalline Run7 TiNi film showed single-stage phase transformation (B19 to B2 on heating and B2 to B19 on cooling).

Theoretical investigation of the magnetic and structural transitions of Ni-Co-Mn-Sn metamagnetic shape-memory alloys

The composition-dependent crystal structure, elastic modulus, phase stability, and magnetic property of Ni2-xCoxMn1.60Sn0.40 (0 <= x <= 0.50) are studied by using first-principles calculations in combination with atomistic spin dynamics method. It is shown that the present lattice parameters and Curie temperature (T-C) are in agreement with the available experimental data. The martensitic phase transformation (MPT) occurs for x < 0.43, where the austenite is in the ferromagnetic (FM) state whereas the martensite is in the antiferromagnetic (AFM) one at 0 K. The x dependence of the lattice parameter, elastic modulus, and energy difference between the FM austenite and the AFM martensite well accounts for the decrease of the MPT temperature (TM) with the Co addition. With increasing x, the increase of the magnetic excitation energy between the paramagnetic and FM austenite of these alloys is in line with the T-C similar to x. The Ni 3d as well as the Co 3d electronic states near the Fermi level are confirmed mainly dominating the phase stability of the studied alloys.

Understanding the martensitic phase transition ofNi2(Mn1−xFex)Gamagnetic shape-memory alloys from theoretical calculations

By using first principles in combination with atomistic spin dynamics calculational methods, we determine the temperature-dependent free energies of the $L{2}_{1}$- and $L{1}_{0}\ensuremath{-}{\mathrm{Ni}}_{2}({\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})\text{Ga}\phantom{\rule{0.28em}{0ex}}(0\ensuremath{\le}x\ensuremath{\le}1)$, including phonon vibrational and magnetic energies. The $x$-dependent martensitic phase transformation (MPT) temperature $({T}_{M})$ and the Curie temperature $({T}_{C})$ are well represented. It is found that, the abnormal nonmonotonic behavior of ${T}_{M}\ensuremath{\sim}x$ mainly originates from the phonon vibrational free energy. The magnetic energy, which does not change the trend of ${T}_{M}$ against $x$ but decreases the driving force of the MPT, is indispensable as well to get reasonable ${T}_{M}$ values. This insight provides a good understanding of the physical mechanisms driving the MPT of ${\mathrm{Ni}}_{2}({\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})\text{Ga}$, and promotes the improvement of their magnetic shape memory properties.

Shifting martensite transformation temperatures of single crystalline Fe72Pd28 thin films by external magnetic fields

The effect of an external magnetic field B on the martensite phase transformation temperature T 0 was studied for single crystalline Fe72Pd28 thin films. From in-plane and out-of-plane aligned magnetic field dependent resistance measurements under various fields up to 9 T, T 0 was determined. The relation between T 0 and B is explained quantitatively by the Clausius–Clapeyron equation. The calculated value of 0.62 K/T is close to the values of the linear fits of 0.79 K/T and 0.76 K/T obtained from measurements with B aligned in-plane and out-of-plane.

Influence of aging on microstructure, martensitic transformation and mechanical properties of NiTiRe shape memory alloy

Aging is an effective way to adapt the microstructure, phase transformation and consequently the mechanical properties of NiTi shape memory alloys. In the present study, Ni52Ti47.7Re0.3 shape memory alloy was solution treated at 1000 °C for 24 h then aged at various temperatures of 300, 400, 500 and 600 °C for 3 h. The influence of aging treatment on microstructure, martensitic transformation and mechanical properties of Ni52Ti47.7Re0.3 was investigated. The microstructure of the solution treated alloy was martensite as a matrix phase and precipitates of Ti2Ni phase. The aged alloys had a microstructure as same as that of solution treated alloy in addition to the existence of other types of precipitates like Ni4Ti3 and Ni3Ti. The martensitic — austenitic transformation during heating and cooling was going through one stage of transformation. The martensitic phase transformation temperature increased by the increase of aging temperature but still lower than that of solution treated alloy.

Calculation of the Pull-Out Force of Ni&lt;sub&gt;47&lt;/sub&gt;Ti&lt;sub&gt;44&lt;/sub&gt;Nb&lt;sub&gt;9&lt;/sub&gt; Shape Memory Ally Pipe Coupling

Investigation of mechanical state of shape memory alloy pipe-coupling had an important significance in engineering field. Theory of plastic deformation was used to analyze the coupling force in the tube connecting process of NiTiNb shape memory alloy, in this paper. Based on the analyzed results a mechanical modeling and formula calculation were carried out, the radial pressure of the SMA tube was calculated, in this paper. The results show that, when the temperature doesn’t reach to contact temperature, the pipe coupling of TiNiNb shape memory alloy has no radial pressure; when the temperature reaches to inverse martensite phase transformation temperature, the radial pressure increases; with the decreasing of temperature, the radial pressure increases a little. The radial pressure and push-out force increase with the increasing of the wall thickness. Thus, to improve the strength of connection, the wall thickness of pipe coupling can be properly increased.

Strain mediated coupling in magnetron sputtered multiferroic PZT/Ni-Mn-In/Si thin film heterostructure

The strain mediated electrical and magnetic properties were investigated in PZT/Ni-Mn-In heterostructure deposited on Si (100) by dc/rf magnetron sputtering. X-ray diffraction pattern revealed that (220) orientation of Ni-Mn-In facilitate the (110) oriented tertragonal phase growth of PZT layer in PZT/Ni-Mn-In heterostructure. A distinctive peak in dielectric constant versus temperature plots around martensitic phase transformation temperature of Ni-Mn-In showed a strain mediated coupling between Ni-Mn-In and PZT layers. The ferroelectric measurement taken at different temperatures exhibits a well saturated and temperature dependent P-E loops with a highest value of Psat ∼ 55 μC/cm2 obtained during martensite-austenite transition temperature region of Ni-Mn-In. The stress induced by Ni-Mn-In layer on upper PZT film due to structural transformation from martensite to austenite resulted in temperature modulated Tunability of PZT/Ni-Mn-In heterostructure. A tunability of 42% was achieved at 290 K (structural transition region of Ni-Mn-In) in these heterostructures. I-V measurements taken at different temperatures indicated that ohmic conduction was the main conduction mechanism over a large electric field range in these heterostructures. Magnetic measurement revealed that heterostructure was ferromagnetic at room temperature with a saturation magnetization of ∼123 emu/cm3. Such multiferroic heterostructures exhibits promising applications in various microelectromechanical systems.