Austenite Transition Research Articles

Effect of heat treatment conditions on the phase transformation characteristics of nitinol

Nitinol is the most widely used shape memory alloy in medical applications. In this study, the effect of different heat treatment conditions on the phase transformation characteristics of medical-grade nitinol was investigated. Nickel-rich nitinol wires containing 50.6% nickel with a diameter of 120 μm were used in the experimental studies. The nitinol wires were heat treated for 10 minutes at heat treatment temperatures between 540 and 570 °C. Then, nitinol wires were heat treated at a heat treatment temperature of 550 °C between 8 and 14 minutes. The austenitic and martensitic transition temperatures of these samples were measured using differential scanning calorimetry (DSC). In the experiments with 10 minutes of heat treatment time, transition temperatures decreased, and hysteresis increased with the increase in heat treatment temperature. This is related to the amount of precipitates in the structure. In the experiments carried out at 550 °C, transition temperatures decreased, and hysteresis increased with increasing heat treatment time. Experimental studies showed that the austenite finish (Af) temperature of all nitinol wire samples was below 37 °C, and they will exhibit superelasticity in the human body.

Role of dislocations on martensitic transformation temperatures and microstructure: A molecular dynamics study

Microstructure and defects strongly affect martensitic transformations in metallic alloys. Significant progress has been made in understanding the atomic-level processes that control the role of grain boundaries and precipitates in these solid-to-solid phase transformations. Yet, the role of dislocations and their structures on martensitic transformation temperature and the resulting microstructure remains unclear. Therefore, we used large-scale molecular dynamics simulations to study the forward and reverse transformation of a martensitic material modeled after Ni63Al37 under cyclic thermal loading. The simulations reveal that dislocations in the austenite phase act as one-dimensional seeds for the martensite phase, which is present at temperatures significantly above the martensite start value. We find a reduction in the dislocation density during cyclic thermal loading, which results in the increase in martensite and austenite transition temperatures, in agreement with experiments. Importantly, we extracted a critical martensitic nuclei size for developing stable domains and found that relatively low dislocation densities are needed to grow independent martensitic variants resulting in a multi-domain structure.

Interfacial structures and properties of sulfide-Fe matrix in steel: A first principles study

Fine sulfides can promote the refinement of microstructure and improve the strength and toughness of materials. The interface properties between sulfides and steel matrix are associated with this phenomenon. The first principles calculation combined with two-dimensional lattice mismatch and two-step nucleation theory is adopted to calculate the interface properties of TiS/bcc-Fe, TiS/fcc-Fe and TiS/MnS at the atomic level. The results show that TiS has a weak ability to promote the transition of austenite to intragranular ferrite (IGF) due to the low adhesion work value. And TiS needs to overcome energy barriers to induce the formation of IGF because the higher interface energy of TiS/bcc-Fe than TiS/fcc-Fe. The heterogeneous nucleation ability of TiS(001)/MnS(111) is stronger than that of TiS(001)/MnS(110), indicating that TiS is beneficial for improving the deformation performance of MnS without affecting the ability of MnS (110) surface to induce IGF nucleation for grain refinement. Based on the two-step nucleation theory, the structures and properties of TiS clusters are analyzed. The formation pathway of TiS/Fe interface can be described as: Tiatom + Satom + Featom → core (TiSn)–shell (fcc-Fe(111)) → core (TiS(001))–shell (fcc-Fe(110) + bcc-Fe(100)).

Investigation of the magnetic and structural properties in the non‐stoichiometric Heusler alloy Ni50Mn25+xSn25‐x; x = 13, 14

AbstractMemory shape magnetic alloys, especially Heusler alloys, are important materials in replacing conventional cooling with magnetic systems. In the present study off stoichiometric Heusler alloys with nominal composition Χ50Υ25+xΖ25‐x (X = Ni; Y = Mn; Z = Sn; x = 13, 14) were prepared by arc melting followed by thermal treatment. Structural properties were analyzed with X‐ray diffraction at room temperature (RT) and at elevated temperatures, above the martensite—austenite transition area, to determine the relevant crystallographic parameters and observe the transition. Martensite stabilization at RT appears to be a challenge, coexistence of martensite—austenite phases were observed and calculated for both 38–12 and 39–11 (16% and 12% austenite, respectively). Magnetization measurements versus temperature and field were recorded in the areas of interest where 1st order transitions were expected (355 K for x = 13 and 408 K for x = 14), and the magnetic entropy's changes (ΔSm) were determined [0.4 (J/kgK) for x = 13 and 0.3 J/(kgK) for x = 14; Hmax = 1 T]. The complex character of the magnetic properties and their dependence on Mn‐Sn ratio and on the distance between Mn atoms is discussed. The structure and the lattice parameters were determined using an anisotropic strain broadening model; stress and strain were detected in the structure due to crystal phase coexistence.

Effect Mechanism of α-Ferrite Sustained Precipitation on High-Temperature Properties in Continuous Casting for Peritectic Steel

Exploring the mechanism of the α-ferrite precipitation process on high-temperature properties plays an important guiding role in avoiding slab cracks and effectively regulating quality. In this work, in situ observation of the α-ferrite sustained precipitation behavior for peritectic steel during the austenitic phase transition process has been investigated using high-temperature confocal scanning laser microscopy. Meanwhile, the high-temperature evolution of the phase fractions during the phase transition process was quantitatively analyzed based on the high-temperature expansion experiment using the peak separation method. Furthermore, the high-temperature properties variations of the casting slab during the α-ferrite sustained precipitation process were investigated with the Gleeble thermomechanical simulator. The results show that the film-like ferrite precipitated along the austenite grain boundaries at the initial stage of phase transition, then needle-like ferrite initiates rapid precipitation on film-like ferrite when the average thickness reaches 15~20 μm. Hot ductility reached a minimum at the ferrite phase fraction fα = 10~15%, while high-temperature properties returned to a higher level after fα > 40~45%. The appearance of a considerable amount of needle-like ferrite and grain refinement effectively improves the high-temperature properties with the α-ferrite precipitation process advances.

Processing, microstructural characterization, and mechanical properties of deep cryogenically treated steels and alloys – overview

Abstract Deep cryogenic treatment (DCT), a technique of deep subzero processing, is utilized after quenching and well preceding tempering. In DCT, the materials are subjected to a soaking period of typically 24 h at a temperature of −196 °C. The optimal soaking period varies depending on the material to be cryotreated. The microstructural characteristics and mechanical properties of ferrous and nonferrous materials are significantly enhanced using DCT resulting in improved durability and functional performance of the mechanical components. The DCT is generally performed on tool steel, stainless steel, aluminum alloys, and magnesium alloys to improve its mechanical properties. The complete transition of residual austenite to martensite and finer secondary carbide precipitation correlates with an increase in the mechanical properties of tool steel. The nonferrous materials such as aluminum and magnesium alloys showed improved mechanical properties owing to the precipitation of finer second phases in the matrix. The main objective of this review paper is to provide an overview on the history and theories of DCT, important processing parameters, and the effect of DCT on microstructure and mechanical properties of tool steel, aluminum alloys, and magnesium alloys.

Comparison and analysis of ProTaper, ProTaper Next, and ProTaper Gold using finite element analysis

Aim: The aim of this study is to compare three endodontic files: ProTaper Universal (PTU), ProTaper Next (PTN), and ProTaper Gold (PTG) under bending forces using finite element analysis. Methods: This study utilizes finite element analysis conducted with ANSYS software. 3D models of the three endodontic files were prepared using ANSYS. A non-linear material model was applied, idealizing the stress-strain curve for Nickel-Titanium alloy (NiTi), the material of these endodontic files. Static and transient analyses were performed to identify three different material phases: austenitic phase, transition phase, and martensitic phase. Results: Finite element analysis reveals that the PTU file exhibited a maximum von Mises stress magnitude of 1249.7 MPa, PTN showed a maximum von Mises stress magnitude of 798.16 MPa, whereas the PTG file showed a minimum von Mises stress magnitude of 465.68 MPa. PTN showed more bending compared to the other file models for the same load magnitude. PTN remained in the austenitic phase until a tip displacement of 7.3657 mm, while PTU reached a maximum displacement of 4.5633 mm in the austenitic phase. Conclusion: The study concludes that the PTU file is the most rigid among the three file models. PTU generates higher stress magnitudes compared to the other files; thus, it is more likely to fracture under lesser bending forces. The study also concludes that PTG exhibits higher displacement with the lowest von-Mises stresses, making it the most flexible file among the three models.

Effects of rapid heating on the phase transformation and grain refinement of a low-carbon mciroalloyed steel

The present study aims to clarify the possibility of rapid heating in the preparation of low-carbon ultrafine (UFG) steel. The effects of heating rate on the phase transformation, microstructure and precipitation of a low-carbon microalloyed steel were elaborately investigated. The results manifest that rapid heating potentially provides a simple and innovative process for the preparation of UFG steels just by increasing the heating rate. The parent austenite grains were refined due to the more reserved (Nb, Ti, V)C precipitates and dislocations within a short heating process by rapid heating. However, an effective holding time was proposed in the rapid heating to ensure the refined austenite grains. Moreover, the synthetic influences of initial increased grain boundaries and redissolved (Nb, Ti, V)C carbides provoked the abnormal grains with weakened thermostability. Redissolution of (Nb, Ti, V)C carbides were apparent during austenite nucleation at a slow heating rate, and it was verified during the isothermal holding stage by rapid heating. In addition, the austenitic phase transition occurred at higher temperature with the increase of heating rate, by which the transformation rate was accelerated.

Reversible shape morphing of a neutrally stable shell by untethered local activation of embedded Ni-Ti wires

This paper presents a novel shape morphing concept, which exploits neutral stability to achieve reversible shape morphing. The concept is based on actively changing the material stiffness on a local level in order to perturb the neutral stability and thus induce the shell to deform. This concept is realized by embedding Ni-Ti wires in a neutrally stable shell. These wires undergo a significant increase in stiffness upon being heated beyond their Austenite transition temperature. The wires are locally heated by forced convection. The results show that the shape of the shell can be controlled freely along the neutrally stable elastic deformation path by changing the location of the heat stimulus. In contrast to existing shape morphing structures, the presented structure is capable of fully reversible (two-way) shape morphing, while also preserving its shape after removing the stimulus. This allows for positioning without continuous actuation. The shell achieves a significant range of motion and, since the elastic deformation reaction forces do not need to be overcome, it is capable of generating actuation force. Since the actuation concept does not require a complex patterning of active materials to achieve the desired deformation, it can potentially also be applied to other neutrally stable structures.

4D forming shape memory component of Cu–13Al–5Fe alloy based on laser powder bed fusion of metal powders

High transition-temperature shape memory alloy (SMA) is widely used in aviation, aerospace and weapon fields. Using commercially available Cu, Al and Fe powders, Cu–13Al–5Fe alloy with high austenite transition temperature of 356–419 °C has been fabricated by laser powder bed fusion (LPBF) and a criterion for formulating the process parameters of LPBF based on the mixture of metal powders has been established. It is found that the LPBF can refine the structure, enhance the mechanical property and shape memory effect (SME). The structure of LPBF formed Cu–13Al–5Fe alloy under the quenched state is composed of tiny β′ martensite distributing in the matrix while the shape memory recovery rate can reach to 100% at the bending sample with 100°, and the shape memory recovery strain can reach to 1.08% under the 5% pre-strain by compressive test. Besides, the compressive stress and strain are 1240 MPa and 15.65% at room temperature. Compared with the arc-melted Cu–13Al–5Fe alloy under the quenched state, its shape memory recovery strain and recovery ratio are increased by 54.2% and 65%, respectively; and its compressive stress and strain are increased by 37.32% and 70.11%, respectively. Considering that, the work provides a criterion and a method for forming the component of Cu–Al–Fe alloy by LPBF based on the mixture of metal powders.

X-ray Line Profile Analysis of Austenitic Phase Transition and Morphology of Nickel-Free Fe-18Cr-18Mn Steel Powder Synthesized by Mechanical Alloying

In this study, microstructural evolution and phase transition of nickel-free Fe-18Cr-18Mn (wt. %) austenitic steel powders, induced by mechanical alloying, were investigated. X-ray diffraction, scanning electron microscopy, and microhardness testing techniques were used to observe the changes in the phase composition and particle size as functions of milling time. The first 30 h of mechanical alloying was performed in an argon atmosphere followed by nitrogen for up to 150 h. X-ray diffraction results revealed that the Fe-fcc phase started to form after 30 h of milling, and its fraction continued to increase with alloying time. However, even after 150 h of milling, weak Fe-bcc phase reflections were still detectable (~3.5 wt. %). Basic microstructure features of the multi-phase alloy were determined by X-ray profile analyses, using the whole powder pattern modeling approach to model anisotropic broadening of line profiles. It was demonstrated that the WPPM algorithm can be regarded as a powerful tool for characterizing microstructures even in more complicated multi-phase cases with overlapping reflections. Prolonging alloying time up to 150 h caused the evolution of the microstructure towards the nanocrystalline state with a mean domain size of 6 nm, accompanied by high densities of dislocations exceeding 1016/m2. Deformation-induced hardening was manifested macroscopically by a corresponding increase in microhardness to 1068 HV0.2. Additionally, diffraction data were processed by the modified Williamson–Hall method, which revealed similar trends of domain size evolutions, but yielded sizes twice as high compared to the WPPM method.

Phase transition kinetics and microstructures of A508-3 steel under continuous cooling process

The phase transition kinetics of A508-3 steel during continuous cooling were studied by high temperature transition instrument which was based on thermodilatometry in this paper. The microstructures during continuous heating and cooling were also observed. The transition points were determined to be austenite formation temperatures, A c1 = 757 °C, A c3 = 823 °C, and martensitic transformation start and final temperatures, Ms = 382 °C, Mf = 222 °C at the cooling rate of 5 °C/s. The curves of Austenite transition fraction and time during continuous heating show a typical S shape. And the Austenite will show a maximum transition rate value at the middle temperature. The volume fraction of new phases translated from Austenite as functions of time and temperature during the cooling process can be obtained using the lever law. The pearlite transitions can occur in high temperature region at cooling rate smaller than 0.1 °C/s. And Bainite can be gotten at a lower temperature region. The S type curves can be used to describe the relationships between the transition volume fraction and time. Increasing the cooling rate enhances the volume fraction of Martensite at the cooling rate ≥5 °C/s. And only Martensite transition can be observed at the cooling rate > 10 °C/s. And Ms and Mf increase with increasing cooling rate. The Martensite transition kinetics equation with changing temperature were obtained. Finally, the continuous cooling transformation curves of A508-3 steel was constructed, which can be used to predict the microstructure and design the heat treatment technologies.

Heat capacity, thermal conductivity and magnetocaloric effect in Heusler alloy Ni-=SUB=-47-=/SUB=-Mn-=SUB=-40-=/SUB=-Sn-=SUB=-13-=/SUB=-

The results of a study of heat capacity, thermal conductivity and magnetocaloric effect of the polycrystalline Ni47Mn40Sn13 alloy depending on temperature (T=80-350 K) and magnetic field (0-8 T) are given. A considerable difference between the values of a sudden change in heat capacity Delta CP in the heating and cooling mode was found near the magnetostructural martensite--austenite phase transition (MSPT), which is related to influence of latent heat of phase transition. Thermal conductivity in the range of T=80-300 K rises with temperature (dkappa/dT>0) and increases in more than three times. Electronic thermal conductivity in the martensitic phase (T=150 K) is 37% of the total value. An anomalous rise of thermal conductivity Deltakappa=kappa(aust)-kappa(mart)=4.2 Wm K was found in the region of MSPT. The contributions of electrons and phonons to the observed sudden change are 63 and 37% respectively and are conditioned both by a rise of mobility of conduction electrons under a martensite--austenite transition and by an increase of phonons' free path length. The magnetocaloric effect in cyclic magnetic fields with the amplitude of 1.8 T was studied. A dependence of reverse effect value on temperature scanning rate was established. The direct measurements of Delta T in the cyclic magnetic field of 1.2 T show a twofold decrease of the effect amplitude near TC at an increase of cyclic magnetic field frequency from 1 to 30 Hz. Most likely, this is related to magnetic and microstructural heterogeneities which act as an additional thermal dissipation channel. Keywords: Heusler alloys, heat capacity, thermal conductivity, magnetocaloric effect, cyclic magnetic fields.

The Kinetics of Phase Transition of Austenite to Ferrite in Medium-Carbon Microalloy Steel

To reduce energy and resource consumption, high-strength hot-rolled rebars with yield strengths of ≥400 MPa (HRB500) and ≥500 MPa (HRB600) have been designed and produced in recent years. Optimizing the microstructure in the steel to improve strength necessitates determining the kinetics of the phase transition of austenite to polygonal ferrite. Therefore, in the study, the effect of temperature and holding time on the volume fraction of ferrite is investigated in HRB500 and HRB600 steels. Experimental results show that the ferrite percentage initially increases with an increase in temperature and then decreases as the temperature increases from 600 to 730 °C. The optimum temperature range is 680–700 °C for HRB500 steel and 650–680 °C for HRB600 steel. Based on the Johnson–Mehl–Avrami equation, phase transition kinetic models are established. Model predictions are consistent with the validation data. Thus, this study establishes a reference for studying ferrite formation during cooling.

Atomistic insight into the solid-solid phase transitions in iron nanotube: A molecular dynamics study

Molecular dynamics (MD) simulations are performed to investigate the austenitic and martensitic transitions in three iron (Fe) nanotubes (NTs) with [100]bcc (NT1), [110]bcc (NT2) and [111]bcc (NT3) axial orientations, respectively. For all NTs studied, the inner and outer surface energies differ slightly and the surface morphologies are analyzed at atomic scale. In NT1, the body-centered cubic (bcc) to hexagonal close packed (hcp) transition is dominated rather than bcc to face-centered cubic (fcc) transition upon heating. The bcc to hcp transition follows the Burgers mechanism and the back transition upon cooling obeys the same pathway. In NT2, the austenitic transition follows the Pitsch mechanism and both the Pitsch and Bain mechanisms are observed during the martensitic transition. In NT3, the bcc ↔ hcp and the bcc ↔ fcc transitions follow the Burgers and Pitsch mechanisms, respectively. In all three cases studied, the nucleation positions of the austenitic and martensitic transitions are discussed referring to the local structures and energetics. Regarding the previous works, we summarize that the transition mechanism tends to be normal strain-controlled rather than shear strain-controlled with the surface-volume ratio increase.

Correlation of magnetocaloric effect through magnetic and electrical resistivity on Si doped Ni–Mn–In Heusler melt spun ribbon

The effect of chemical substitution of Si on Mn site in Ni47Mn40-xSixIn13 (x = 1, 2 & 3) melt spun ribbons on the structure, electrical, magnetic and magnetocaloric studies are investigated. All the synthesized ribbons exhibits austenite phase at room temperature. It is found that the increase of Si content under applied magnetic fields of 0.05 T and 5 T shifts both the Curie transition temperature of the austenitic phase (TCA) and martensitic phase transition temperature (TM) towards lower temperatures. The splitting of ZFC and FC curve during magnetic measurements exposes exchange bias phenomenon attributed to irreversibility nature of magnetization due to inhomogeneous magnetic anisotropy below the blocking bias temperature. The large magnetic entropy change (ΔSM) is observed across the martensite transformation and a maximum magnetic entropy change (ΔSM)max of 10 Jkg−1K−1 is obtained for x = 1 ribbon at 273 K with a magnetic field change of 5 T. Upon further increase of Si content, the (ΔSM)max values are found to decrease from 6.3 Jkg−1K−1 (x = 2) to 5.54 Jkg−1K−1 (x = 3) and the same trend is observed for ΔSMm-ρ values.

Martensitic transformation, magnetic and magnetocaloric properties of Ni–Mn–Fe–Sn Heusler ribbons

Melt-spun ribbons of nominal composition Ni50Mn36-xFexSn14 (x = 0, 2, and 3) were prepared by melt-spinning. The alloys undergo a martensitic transformation from L21 austenite to an orthorhombic 4O martensite on cooling, as determined by X-ray powder diffraction analysis. Replacement of Mn by Fe linearly reduces the characteristic temperatures of the martensitic transformation (the equilibrium temperature decreases from 328 to 285 K) and reduces the Curie temperature of the austenite phase (from 336 to 300 K), whereas the effect of the applied magnetic field on the martensite transition temperatures is negligible. Magnetic measurements (zero-field cooled, ZFC, and field cooled, FC, curves, AC susceptibility measurements) hint the coexistence of two different ferromagnetic martensitic magnetic phases. Moreover, the AC susceptibility measurements and the irreversibility of the ZFC and FC curves point towards the presence of antiferromagnetic and ferromagnetic interactions in the martensitic phase. All samples exhibit spontaneous exchange bias at 2 K, with double-shifted loops, whereas the evolution of the conventional exchange bias with the temperature agrees quite well with the behavior of ferromagnetic regions surrounded by spin-glass regions or with the coexistence of ferromagnetic–antiferromagnetic interactions. Ni50Mn36-xFexSn14 ribbons present a moderate inverse magnetocaloric effect (with a maximum of the magnetic entropy change of 5.7 Jkg−1K−1 for μ0H = 3 T for x = 3). It is worth to note that these materials feature a significant reservoir (up to 44 Jkg−1K−1 for x = 2) of magnetic entropy change, linked to the proximity of the austenitic ferromagnetic transition to the martensitic transformation.

Influence of tool characteristics on white layer produced by cutting hardened steel and prediction of white layer thickness

In the dry and hard cutting process of hardened steel, the white layer of the machined surface has a great influence on the service performance and life of the part. The cutting force and cutting heat produced in the process are among the important factors affecting the white layer characteristics. In the process of machining, in addition to the cutting parameters, the characteristics of cutting tools can also lead to significant changes in both service performance and part lifetime. Therefore, it is necessary to further study the changes in the cutting force, cutting heat, and white layer characteristics under the influence of the tool characteristics. In this paper, hard cutting tests of hardened steel were carried out by cutting tools (including PCBN tools and ceramic tools) with different thermal conductivities and flank wear under different cutting speeds. The influence of the cutting speed and tool characteristics on the cutting force, flank temperature and white layer characteristics was analyzed, and a prediction model for the white layer thickness was established. It was found that the cutting speed, tool wear degree, and tool thermal conductivity all have a significant influence on the cutting force, cutting temperature, and white layer thickness. Among the results, the thickness of the white layer first increases and then decreases with increasing flank temperature, and the critical temperature at the maximum thickness of the white layer is the actual final temperature of austenite transformation. Changes in the cutting force indirectly affect the temperatures of the austenite and martensite phase transitions, thus affecting the thickness of the white layer. The prediction results show that a fuzzy neural network based on particle swarm optimization can effectively predict the thickness of the white layer.

Thermoelastic properties across martensitic transformation of Ni[formula omitted]MnGa Heusler alloy from time-resolved photothermal mirror

We report on the thermoelastic properties of Ni2MnGa shape-memory alloys across the martensitic to austenitic phase transition using the time-resolved pump–probe photothermal mirror technique. Quantitative information on the thermo-mechanical characteristics of the sample are obtained and compared to specific heat measurements and differential scanning calorimetry (DSC) analysis. The thermal diffusivity varied remarkably within the martensitic–austenitic transition range. Both the amplitude signal and the thermal diffusivity present, in addition to the strong martensite to austenite phase transition, a clear evidence of a subtle second-order type phase transition close to 80 °C. This magnetic transition is also observed in the calorimetric analysis. The transformation temperatures suggest the non-stoichiometric composition of sample, which is also revealed by non-symmetrical shapes of DSC peaks. The possible variation of the local chemical composition could be a result of gallium loss during the sample preparation or local inhomogeneity in the martensitic transformation.

Glassy Magnetic Transitions and Accurate Estimation of Magnetocaloric Effect in Ni-Mn Heusler Alloys.

In this work, the structural and magnetic transitions of Heusler alloy Ni50Mn34In14Ga2 have been carefully studied through measurements of heat flow and magnetization under DC and AC magnetic fields. This alloy undergoes the transition sequence of spin-glassy martensite (SPM) → ferromagnetic austenite (FA) → paramagnetic austenite at ∼225 and ∼305 K, respectively, during heating. Splitting of zero-field-cooling (ZFC)/field-cooling (FC) curves in martensite is caused by the slowdown dynamics of spin glass as evidenced by frequency dispersion and aging effects. The development of a spin-glass state is believed to be the result of strain relaxation and interaction of ferroelastic twin walls in the martensite. The magnetocaloric effect (MCE) at the SPM-FA transition was then measured using indirect, quasi-direct, and direct methods. The MCE magnitudes are controlled by the entropy changes associated with the first-order martensite transition and magnetic ordering of austenite under the magnetic field. The existence of a spin-glass state in martensite can also improve the reversibility of the magnetostructural transitions, which is beneficial for the improvement of the reversibility of associated MCE. These results provide an in-depth understanding of the transitions and magnetic properties of the Ni-Mn Heusler alloys and suggest that the MCE at the first-order magnetostructural transitions estimated solely using indirect methods may need some revision.