Direct Martensitic Transformation Research Articles

Ultraslow calorimetric studies of the martensitic transformation of NiFeGa alloys: detection and analysis of avalanche phenomena

AbstractWe study the thermal properties of a bulk $$\hbox {Ni}_{55}\hbox {Fe}_{19}\hbox {Ga}_{26}$$ Ni 55 Fe 19 Ga 26 Heusler alloy in a conduction calorimeter. At slow heating and cooling rates ($$\sim {1}\,\hbox {K h}^{-1}$$ ∼ 1 K h - 1 ), we compare as-cast and annealed samples. We report a smaller thermal hysteresis after the thermal treatment due to the stabilization of the 14 M modulated structure in the martensite phase. In ultraslow experiments ($${40}\,\hbox {mK h}^{-1}$$ 40 mK h - 1 ), we detect and analyze the calorimetric avalanches associated with the direct and reverse martensitic transformation from cubic to 14 M phase. This reveals a distribution of events characterized by a power law with exponential cutoff $$p(u)\propto u^{-\varepsilon }\exp (-u/\xi )$$ p ( u ) ∝ u - ε exp ( - u / ξ ) where $$\varepsilon \sim 2$$ ε ∼ 2 and damping energies $$\xi ={370}{\upmu {\rm J}}$$ ξ = 370 μ J (direct) and $$\xi ={27}{\upmu {\rm J}}$$ ξ = 27 μ J (reverse) that characterize the asymmetry of the transformation.

Investigating the reversible nature of the magnetocaloric effect under cyclic conditions of the Ni50Mn34In15Ga1 magnetic shape memory alloy

This study explores the reversibility of the martensitic transformation (MT) and magnetocaloric (MC) response of the Ga-doped Ni50Mn35In15 magnetic shape memory alloys (MSMAs) with a Heusler structure. The direct and reverse MT occurs between temperatures TM ≈ 257 K and TA ≈ 266 K, respectively. The large MC effects resulting from the magnetic-field-induced first-order MT render these materials promising for room-temperature magnetic refrigeration. On account of both a low thermal hysteresis of MT (ΔThyst = 4 K) at a magnetic field of 2 T and a highly reproducible peak value of the adiabatic temperature change at MT (|∆Tad| ≈ 1.3 K for µ0H = 1.9 T), Ni50Mn34In15Ga1 MSMA emerges as a benchmark material for studying a cyclic stability of MC effects. During the first magnetic switching cycle, a reduction of ∆Tad at MT by approximately 1.3 is observed, significantly lower than the reported one for other MC materials undergoing similar first-order phase transitions. Subsequent cycles revealed a consistent stability of the magnetic-field-induced ∆Tad even after more than 200 magnetic field switching cycles. These findings suggest a notable degree of reversibility of the MT in the studied MSMA, which was also confirmed in the present work by a Temperature-First Order Reverse Curve distribution analysis.

New insights into the effects of solidification process on the thermodynamic parameters and mechanical properties of CuAlBeNbNi shape memory alloy

In this work, the influence of the processes of unidirectional solidification and squeeze casting in microstructure, thermodynamic parameters and mechanical properties of CuAlBeNbNi shape memory alloy (SMA) was investigated. The results show that the unidirectional solidification process causes an increase in phase transformation temperatures and ductility, improves fracture toughness and reduces stress-induced martensite, residual stress and dissipated energy after load-unload tensile test of the CuAlBeNbNi alloy. The squeeze casting process, on the other hand, causes an increase in the density of grain boundaries, increasing the stress-induced martensite and the elastic energy of the direct martensitic transformation, while decreasing the impact toughness, increasing the residual deformation, the residual stress and the dissipated energy after the tensile cycle tests. These results indicate that the processes of unidirectional solidification and squeeze casting offer an alternative method to modify the thermodynamic parameters, mechanical properties, and microstructural properties of the CuAlBeNbNi SMA while keeping the composition constant. This study aims to fill the knowledge gap regarding the impact of solidification processes on the properties of Cu-based SMAs, specifically investigating CuAlBeNbNi SMAs.

Экспериментальное исследование и теоретический анализ потери устойчивости пластин из никелида титана, обусловленной прямым термоупругим фазовым превращением под действием сжимающей нагрузки

The results of experimental studies of the dependence of the critical load of stability loss of rectangular titanium nickelide plates, experiencing a direct martensitic phase transformation under the action of a constant compressive load on the length of the plate, are presented. Within the framework of various formulations and concepts, an analytical solution of the corresponding stability task has been obtained. It is established that the best correspondence with experimental data is obtained when solving the task in a single-coupled formulation, within the framework of the concept of a ubiquitous additional phase transition.

The thermo-mechanical behavior of NiTi-X shape memory alloys

A commercial NiTi alloy with the chemical composition of 54.5 Ni-45.5 Ti (mass %) was used as a standard material to be compared with Ti50Ni45Cu5, 48 Ni-37 Ti-15 Nb (mass. %) and 48 Ni- 37 Ti-15 Ta (mass. %). The experimental alloys were cast, annealed and hot rolled in order to render the material more compact and to obtain 0.5 mm-thick lamellas. Two types of specimens were then obtained. The former were fragments with a mass of less than 50 mg that were cut and cleaned in alcohol, in an ultrasonic bath, before being subjected to differential scanning calorimetry (DSC) analysis. The latter were 0.5 × 4 × 25 mm rectangular specimens that were prepared to be subjected to dynamic mechanical analyses (DMA) and optical analysis (OM). The DSC investigation program comprised a heating–cooling cycle with a rate of 10 K/min and was used in order to obtain the critical transformation temperatures of direct and reverse martensitic transformations. DMA measurements consisting in a heating cycle with a heating rate of 5 K/min, a frequency of 1 Hz, a maximum deformation of 20 µm and a maximum of 9 N dynamical applied force, were used in order to observe the mechanical behavior under dynamic conditions. DSC tests suggested that Cu and Ta alloying led to an increase of critical temperatures of reverse martensitic transformation while Nb alloying dropped these critical temperatures as low as 0 °C. In addition, Ta alloying significantly increased the transformation temperatures. All the DMA thermograms emphasized a maximum of internal friction that could be associated with the reverse martensitic transformation. Storage modulus exhibited either continuous or step-like increase during heating, suggesting the presence of a thermoelastic transformation.

Thermokinetics of shape recovery of nanostructured titanium nickelide

The microstructure, martensitic transformations (MTs), functional characteristics and thermokinetics of shape recovery of Ni-rich titanium nickelide was studied. Post-deformation annealing at a temperature of 823 K (30 min) after cold drawing with the accumulated logarithmic strain of 0.6 forms a mixed nano-sized grain / subgrain structure of B2 austenite. The training procedure was carried out using isothermal and non-isothermal bending modes. The loading-unloading temperatures were associated with the characteristic temperatures of MTs; the loading strain was varied in the range of 13 –19 %. The specific features of the evolution of functional characteristics when using various loading modes are described. The strain-temperature conditions for the realization of the total shape recovery 17 % and TWSME value 4 % are revealed. The two-stage character of shape recovery after unloading is revealed; the hypothesis of its origin is suggested. The start and finish temperatures of shape recovery vs loading strain are measured. When using the non-isothermal mode with deep cooling under load, the temperature range for shape recovery expands from 35 to 77 K with increasing loading strain. When using the isothermal mode with loading-unloading at a start temperature of the direct MT, the temperature range of shape recovery degrades from 66 to 54 K.

Effect of magnetic field on thermal strain, thermal expansion and negative thermal expansion property in a polycrystalline Ni55Mn18Ga27 alloy

The magnetic field effect on phase transition and thermal expansion properties were investigated in Ni55Mn18Ga27 alloy. The results show that the alloy has an excellent isotropy, reproducibility and thermostability in thermal strain and exhibits a large negative thermal expansion (NTE) effect in the direct and reverse martensitic transformations (MTs). For the direct MT, the average linear expansion coefficient α is about −225.21 ppm/K and the corresponding temperature span is around 8.2 K. Additionally, the sensitivities of the transformation strain and peak temperatures to field are about 88.5 ppm/T and 1.31 K/T, respectively. The rates of α and temperature spans of NTE to magnetic field are about 8.88 ppm/K T and 0.82 K/T, indicating that the magnetic field can improve the NTE property of the Ni–Mn-Ga alloy. Finally, the NTE mechanism has also been discussed. Our findings are beneficial to improving the thermal expansion and NTE properties of Ni–Mn-Ga alloys.

Preparation of porous TiNi-Ti alloy by diffusion sintering method and study of its composition, structure and martensitic transformations

The study demonstrates a method for controlling not only the phase composition but also the atomic composition of TiNi matrix in porous TiNi-Ti alloys developed for biomedical uses as implants. The alloys were obtained from TiNi powder which was sintered with Ti powder added at as much as 0–10 at%. The structure, phase and chemical composition of the produced TiNi-Ti alloys was investigated with respect to the amount of Ti added into the material. It is shown that in the sintered product containing 5 at% and more of Ti additive, the composition of its TiNi matrix becomes close to equiatomic (with Ti:Ni atomic ratio ~1), and the excessive Ti precipitates as secondary phases Ti2Ni and Ti3Ni4. In parallel, with increase in Ti additive from 0–10 at%, the structure of the precipitating Ti2Ni type phases changes its morphology from separate spherical or pyramidal precipitates to large dendritic formations. The direct martensitic transformation from austenite to martensite in all the samples was found to proceed in two stages and through the R-phase (B2→R→B19′). Thermoresistive analysis demonstrated that TiNi-Ti samples with 5 and more at% of Ti had their characteristic starting temperature of martensite transition stabilizing at ~57 °C (330 K). This implies that the sample with 5 at% of Ti additive exhibited desired martensite transition temperatures, while containing a minimum concentration of secondary-phase precipitates in its matrix which deteriorate its properties. Thus, for the first time, we show that a very simple preparation approach based on sintering powders of TiNi and Ti is capable of producing porous TiNi-Ti alloys with properties optimized for fabricating bone implants.

Влияние обратного термоупругого фазового превращения на напряжение начала структурного превращения в никелиде титана

The experimental study results of the dependence in the stress value of the onset of the structural deformation on the degree of the reverse phase transformation occurring after the complete direct martensitic transformation in titanium nickelide are described. It is established that these results are qualitatively and quantitatively correctly described in the framework of the model according to which the maximum value of the intensity of the intrinsic inelastic deformation of the martensitic part of the representative volume of the shape-memory alloy is used as a parameter of isotropic hardening.

Effect of annealing temperature and time on martensitic transformation temperatures and mechanical properties of the Ti–50.7at.%Ni shape memory alloy

The study covers the effect of recrystallization annealing temperature and time on the characteristic temperatures of martensitic transformations and mechanical properties of the Ti–50.7at.%Ni shape memory alloy in the form of wire after cold drawing at room temperature. Six modes of post-deformation annealing with different temperatures and holding times were studied for the alloy to obtain structures with different sizes of recrystallized grains. The recrystallized grain size was determined by electron backscatter diffraction (EBSD). It was shown that the size of recrystallized grains increases from 2.5 to 9 μm, with both an increase in the annealing temperature (600– 700 °С) and an increase in the holding time (0.5–5.0 h). The characteristic temperatures of direct and reverse martensitic transformations were determined using differential scanning calorimetry. It was shown that the threefold growth of the recrystallized grain size reduces the starting temperature of the direct martensitic transformation, and extends the temperature range of the reverse martensitic transformation. The results of mechanical tests (stretching tests) at room temperature showed that an increase in the grain size leads to a decrease in the dislocation yield strength and an increase in the phase yield strength. It was established that the dislocation yield strength obeys the Hall–Petch law, and the phase yield strength is determined by the test temperature position relative to the starting (or peak) temperature of the direct martensitic transformation. Heat treatment modes for specific products should be recommended taking into account these two competing factors, as well as reverse martensitic transformation temperatures determining the alloy strain recovery temperatures.

Direct measurement and imaging of magnetocaloric effect inhomogeneities at the microscale in Ni44Co6Mn30Ga20 with infrared thermography

To study the MCE at the microscale with infrared thermography, a bulk Ni44Co6Mn30Ga20 sample was investigated. Direct measurements of the MCE were performed for temperatures around the reverse and direct martensitic transformation, by applying and removing a ~1.2 T magnetic field to the sample and recording the changes in its surface temperature with an IR camera. This was done for different sample temperatures on heating (from 273 K to 327 K) and cooling (from 327 K to 267 K).For sample temperatures around the reverse martensitic transformation, the inverse MCE is observed, with ΔT between −0.04 K and −0.54 K. The effect displays strong spatial inhomogeneity at the microscopic scale, which varies considerably with the progress of phase transformation. This behavior is not observed for the direct martensitic transformation (on cooling).The study reveals substantial novelty in the manifestation of the MCE at the microscopic scale, associated with phase dynamics, showing a different and inhomogeneous behavior on heating and cooling of a FSMA around the martensitic transition.

Мартенситные превращения и эффект памяти формы биосовместимых сплавов TiNiMoAl

A study of martensitic transformations and characteristics of the shape memory effect of medical alloys (TH-10) alloyed with aluminum up to 4 at.% Al long the TiNiMo-TiMeMo section was carried out. Aluminum has a fairly smooth effect on the temperatures of the beginning and end of the direct and reverse martensitic transformation, as well as similar characteristics under load, which makes it possible to use alloying with aluminum as a method for controlling the temperature range of shape change with the shape memory effect.

Martensitic Transformations of the Titanium–Nickelide Alloys with Different Alloying Additions

Martensitic transformations of the TN-10 titanium-nickelide alloys doped with V, Nb, and Ag at a level of 1 at % are studied. It is shown that the alloying elements (Ag, Nb, and V) cause an increase in the elastic stress inside the B2-phase structure and the consequent increase in the start temperature of the direct martensite transformation. Vanadium significantly affects such a temperature and provides an increase by about 45°C. Complicated martensite transformations (B2 → R → B19') take place in alloys with vanadium and silver, and simple transformations (B2 → B19') occur in alloys with niobium.

Buckling of a Rod with a Circular Cross Section Induced by a Direct Thermoelastic Martensitic Transformation

Buckling of a Rod with a Circular Cross Section Induced by a Direct Thermoelastic Martensitic Transformation

Мартенситные превращения сплавов на основе никелида титана с разными легирующими добавками

Investigations of the martensitic transformations of TiNi-based alloys grade TN-10, doped with 1 at.% V, Nb, Ag, were presented. It was shown that alloying elements (Ag, Nb, V) cause an increase in internal elastic stresses inside the crystalline structure of the B2 phase, which leads to an increase in the beginning temperature of direct martensitic transformation. Of the selected alloying elements, vanadium has a significant effect on this temperature, shifting it to the region of high values ​​by ~ 45 ° C. In alloys with vanadium and silver, a complex sequence of martensitic transformations B2-> R-> B19 'is realized, and in alloys with niobium, a simple B2-> B19' is realized.

Потеря устойчивости стержня круглого поперечного сечения из никелида титана, вызванная прямым термоупругим мартенситным превращением

Потеря устойчивости стержня круглого поперечного сечения из никелида титана, вызванная прямым термоупругим мартенситным превращением

Cross Hardening of a Shape Memory Alloy during Compression

Abstract—The influence of the preliminary direct martensitic transformation in titanium nickelide under a constant compressive stress on the diagrams of subsequent loading under martensitic inelasticity at a monotonically increasing compressive stress is experimentally studied. These diagrams are found to reach the martensitic inelasticity diagram corresponding to the compression of initially fully twinned martensite when the stress increases. The cross hardening on compression is shown to be more intense than that on tension. The phase-structural strain deviator can be considered as a state parameter for a shape memory alloy.

Experimental Identification of a Nonlinear Deformation Model for a Shape Memory Alloy during Phase and Structural Transformations

The deformation of titanium nickelide specimens in loading under the conditions of martensite inelasticity and direct martensitic transformation during uniaxial compression and tension is experimentally studied. The experimental results can be used to determine two material functions for a nonlinear deformation model for a shape memory alloy. The experimental data are found to be approximated best of all when cumulative γ distribution functions are applied.

Effect of the temperature and magnetic field induced martensitic transformation in bulk Fe45Mn26Ga29 alloy on its electronic structure and physical properties

Effect of the temperature and magnetic field induced martensitic transformation (MT) on the electronic structure and some physical properties of bulk Fe45.2Mn25.9Ga28.9 Heusler alloy has been investigated. According to the experimental results of DSC, magnetic and transport measurements direct and reverse martensitic transformation without external magnetic field takes place within 194 ≤T≤ 328 K temperature range with a hysteresis up to ΔT≈ 100 K defined as ΔT = Af,s - Ms,f, where Af,s and Ms,f are the critical temperatures of direct and reverse martensitic transformation. External magnetic field of μ0H = 5 T causes a high-temperature shift of MT temperatures. MT from parent austenite L21 phase to martensitic tetragonally distorted L21 one (i. e. to L10) causes significant changes in the electronic structure of alloy, a drastic increase in alloy magnetization, a decrease in the alloy resistivity, and a reversal of the sign of the temperature coefficient of resistivity from negative to positive. At the same time experimentally determined optical properties of Fe45.6Mn25.9Ga28.9 Heusler alloy in austenitic and martensitic states look visually rather similar being noticeable different in microscopic nature as can be concluded from first-principle calculations. Experimentally observed changes in the physical properties of the alloy are discussed in terms of the electronic structures of an austenite and martensite phases.

Numerical modeling of the 22MnB5 formability at high temperature

Abstract It has been recognized in automotive sector that the use of hot stamped parts for the automobile body-in-white allows significant weight saving and reduction of CO2 emissions. The weight reduction is accompanied by high stiffness and increased crashworthiness, which improve the passengers’ safety and allow the development of more complex vehicle’s design. In direct hot stamping, the 22MnB5 sheets are heated above the austenitization temperature, and then, formed and quenched in cooled dies by using a minimum cooling rate of 27°C/s in order to obtain the direct martensitic transformation from the initial austenite. To evaluate part feasibility, minimize production cost and improve process robustness in hot stamping, numerical simulations are becoming increasingly important, where data regarding the formability of the material at high temperature plays a central role in the simulation. A survey of the literature shows that the complex aspects of the process have been extensively investigated from an experimental point of view, but limited studies concerning the numerical modeling of the process can be found. The aim of the present paper is to explore the critical aspects of the numerical modeling in terms of material formability in hot stamping. Numerical simulations of hot Nakajima tests at the critical temperature of 600°C were performed by using explicit numerical method, while experimental tests are carried out in the same condition. The comparison of the numerical results and the experimental data demonstrates the influence that the thermal cycle applied during the experimental tests may have, since it governs the phase transformations that affect the material formability.