Martensite-austenite Phase Transition Research Articles

The defects and compressive behavior of NiTi alloy fabricated by laser powder bed fusion under a wide process space

A wide process space with laser power (P) of 50 ～ 400 W and scanning speed (s) of 50 ～ 2400 mm/s with the energy density (ED) range of 93–556 J/mm3 has been employed to fabricate NiTi alloy using laser powder bed fusion (LPBF). The optimal process window for near-full dense materials free of geometrical and metallurgical defects was determined. The characteristics of microstructures and compressive behaviors were comprehensively investigated. The results have shown that the process combinations of “high P + low s” and “high P + high s” are prone to bulging and warping defects due to rapid heating and cooling, respectively. A combination of “low P + low s” produces a relatively shallow melt pool without keyhole formation even at ED as high as 556 J/mm3. The austenite-martensite phase transition temperature (TTs) variations of ～80℃ were obtained with the process window free of porosity. The pre-existing martensite lath probably formed by plastic distortion (bulging) was responsible for the lowest critical stress of induced martensite (σSIM). The texture and nano-sized NiTi2/Ni2Ti4Ox precipitates also contribute to the variation of σSIM and residual strain among the samples with the same level of TTs upon compressive loading.

Structure and magnetic properties of Ni–Mn–Ga shape memory alloys

In this paper, we present structure, structural phase transformation, magnetic phase transition, and magnetocaloric effect of Ni50Mn50-x Ga x (x = 17, 18, 19, 20, and 21) shape memory alloys. X-ray diffraction patterns display nano-crystalline phases in the alloys. The samples are soft magnetic material with very narrow magnetic hysteresis. The martensitic-austenite transformation temperature increases from 219 K (for x = 17) to 322 K (for x = 21) with increasing Ga-concentration. Ga also increases the Curie phase transition temperature and the saturation magnetisation of the alloy. The external magnetic field also clearly affects the structural phase transition of the alloy. The magnitude of the martensitic-austenitic phase transition decreases with the increase of the applied magnetic field. Both the normal and invert magnetocaloric effects coexist in the alloy. Under the magnetic field change of 10 kOe, the maximum magnetic entropy change, ∣ΔS m ∣max, for the Ni50Mn30Ga20 ribbon is 0.95 J.kg−1.K−1 for the normal magnetocaloric effect.

Anomalous heat transfer near the martensite-austenite phase transition in Ni50Mn28Ga22-x(Cu, Zn)x (x = 0; 1.5) alloys

The paper presents a detailed investigation of the thermal transport of the Ni50Mn28Ga22-x(Cu, Zn)x (x = 0; 1.5) alloys through specific heat, thermal diffusivity and thermal conductivity measurements. It is shown that the partial replacement of Ga atoms by Zn or Cu atoms leads to a convergence of magnetic and martensitic phase transition temperatures. Our measurements of the thermal diffusivity and thermal conductivity revealed that the behavior of these parameters in the phase transitions region is anomalous due to the coexistence of martensite-austenite phases and the effect of the latent heat of the phase transition. Moreover, the latent heat plays a crucial role in the appearance of a deep minimum of thermal diffusivity in the region of martensitic transformation for the Cu- and Zn-doped samples. Estimates of the phonon mean free path lph in martensitic and austenitic phase gave values of lph,mart = 1.5 nm and lph,aust = 1.9 nm, respectively. This implies that the main mechanism of phonon scattering is local structural inhomogeneities, which decrease sharply upon transition from martensite phase to the highly symmetric austenitic phase.

Metamagnetic transition and magnetocaloric properties of Ni45Mn42In13 Heusler alloy

ABSTRACT We report a study of the metamagnetic transition and magnetocaloric effect in the ternary Ni45Mn42In13 Heusler alloy system. We also investigate the structural and magnetic properties of the alloy. The crystal structure exhibited a mixture phase of martensite and austenite at room temperature which are typical for Heusler alloys. The thermomagnetization curves have martensitic and magnetic transition near room temperature and with a quite large magnetization value under 5 T applied external magnetic field. The obvious reversible metamagnetic behavior was seen between 285 and 295 K temperatures. The isothermal M–H curves also confirmed the metamagnetic transition and provided the magnetocaloric effects by Maxwell relations. This system underwent an austenite–martensite phase transition and the change in magnetic entropy was found to be quite large across this martensitic transition, so this led to an inverse magnetocaloric effect. Significant maximum magnetic entropy was obtained under 5 T applied magnetic field.

Prediction of a Heusler alloy with switchable metal-to-half-metal behavior

We propose a ferromagnetic Heusler alloy that can switch between a metal and a half-metal. This effect can provide tunable spintronics properties. Using the density functional theory with reliable implementations of the electron correlation effects, we find ${\mathrm{Mn}}_{2}\mathrm{ScSi}$ total energy curves consisting of distinct branches with a very small energy difference. The phase at low lattice crystal volume is a low magnetic half-metallic state while the phase at high lattice crystal volume is a high magnetic metallic state. We suggest that the transition between half-metallic and metallic states can be triggered by a triaxial contraction/expansion of the crystal lattice or by an external magnetic field if we assume that the lattice is cubic and remains cubic under expansion/contraction. However, the phase at high volume can also undergo an austenite-martensite phase transition because of the presence of Jahn-Teller active $3d$ electrons on the Mn atoms.

A thermo-mechanically coupled finite strain model for phase-transitioning austenitic steels in ambient to cryogenic temperature range

We present a finite-strain thermo-mechanically coupled continuum theory to model the material response of phase transitioning (metastable) austenitic steels from ambient (room) to cryogenic temperature. We applied our model to 316L stainless steel which shows plastic strain driven transformation from FCC austenite to BCC martensite phase at temperatures below room temperature and calibrated the model parameters using uniaxial tension tests at room and cryogenic temperatures. The constitutive model is able to successfully model the observed second strain-hardening behavior at cryogenic temperature due to formation of harder martensite at large strains. We implemented our coupled thermo-mechanical-phase transition model in the finite element program Abaqus by writing a user material subroutine and validated the model by conducting finite element based tension and compression simulations for a room temperature formed corrugated pipe. Comparisons of mechanical response between our simulation predictions and full-scale tests for the corrugated pipe at both room and cryogenic temperature show good accuracy of our model. We also conducted simulations to investigate the austenite-martensite phase transition near a notch tip in a flat plate geometry.

Influence of Co and Al on Magnetic Properties and Magnetocaloric Effect of (Ni, Co)-Mn-(Sn, Al) Alloys

This paper investigates the influence of Co and Al concentrations on the structure, magnetic properties and magnetocaloric effect of (Ni, Co)-Mn-(Sn, Al) alloy ribbons prepared by melt-spinning. X-ray diffraction analyses show multi-crystalline phase characteristic of the ribbons including face-centered cubic (L10), body-centered cubic (B2), orthorhombic (4O) and monoclinic (10M) phases. The amplitude and temperature of the martensite–austenite phase transition of the alloy clearly depend on Co and Al concentrations. Magnetization measurements reveal soft magnetic features, with coercivity less than 50 Oe for all the alloy ribbons. The Curie temperature of the austenite phase increases with increasing Co concentration, but decreases with increasing Al concentration. The magnetic phase transitions in the alloy can be shifted to the room temperature region by adjusting the Co and Al concentrations. With appropriate concentrations of Co and Al, the alloy ribbons possess both negative and positive magnetocaloric effects, with a maximum magnetic entropy change larger than 0.6 J kg−1 K−1 in a magnetic field change of 12 kOe. The temperature and magnetic field dependence of the magnetocaloric effect in these alloy ribbons was also investigated.

The mechanical cycling behavior of TiNi based crystal/glassy alloy in the superelastic mode

We designed TiNi bulk metallic glass composite (BMGC) which has both a glassy phase and a crystalline phase. The TiNi BMGC undergoes a martensitic transformation during deformation, exhibits the superelastic behavior and excellent mechanical properties: strength of 2.5 GPa, ductility of more than 20%. It is known that mechanical-fatigue is an important feature which affects the martensitic transformation during superelastic cyclic loading. Comparison of the fatigue performances in TiNi dual-phase alloy and TiNi fully crystalline alloy demonstrates that the amorphous phase acts as the barrier and sinking of the dislocation slipping and promotes martensite-austenite phase transition during the superelastic cycling. The representative BMGCs provide a way to design metallic glasses with high ductility and outstanding anti-fatigue properties.

Long-range ferromagnetism and magnetocaloric effects in rapidly quenched Ni 50−x Co x Mn 50−y Al y ribbons

Abstract Ni50−xCoxMn50−yAly (x = 7 and 9; y = 17, 18 and 19) alloy ribbons were prepared by melt-spinning with a tangential velocity of copper wheel of 40 m s−1. X-ray diffraction patterns reveal multi-crystalline phase behavior in the fabricated ribbons. The shape of thermomagnetization curves clearly depends on Co and Al concentrations. The Curie temperatures (TC) of the alloy ribbons strongly increase with increasing the Co concentration and slightly decrease with increasing the Al concentration. The martensitic-austenitic phase transition in the alloy ribbons can be manipulated by tuning Co and Al concentrations. The maximum magnetic entropy change |ΔSm|max of about 0.75 J kg−1 K−1 for a field change of 12 kOe at TC ≈ 364 K was achieved for the Ni43Co7Mn32Al18 ribbon. Critical analysis using the Arrott-Noaks and Kouvel–Fisher methods demonstrates the existence of a long-range ferromagnetic order in this ribbon.

Effect of Cu substitution on magnetocaloric and critical behavior in Ni47Mn40Sn13−Cu alloys

Abstract A series of Heusler phases Ni47Mn40Sn13−xCux (x = 0, 0.5, 1, 1.25), which are magnetic shape-memory alloys, has been synthesized by mechanical alloying (MA) and characterized. The martensite-austenite phase transition was investigated by X-ray diffraction, differential scanning calorimetry, and DC magnetization measurements. With greater Cu content, the martensitic transition temperature TM increases while the magnetic transition temperature of austenite T c A remains almost unchanged. The maximum inverse magnetic entropy changes Δ S M for the x = 0.5 and x = 1 samples are nearly twice as high as for the undoped sample. Furthermore, the martensitic transformation of the doped samples occurs around room temperature, which is important for applications. Effective refrigerant capacities (RCeff) reduced due to the higher hysteresis losses in the x = 0.5 and x = 1 samples compare to the undoped one. Refrigerant capacities (RC) were examined in T c A . The largest value of RC = 207 J/kg was measured for the undoped sample. Critical properties near the ferromagnetic–paramagnetic (FM–PM) phase transition were analyzed in detailed. The critical parameters β, γ, δ and T c A of the x = 0 and x = 0.5 samples, which were determined through use of modified Arrott plots, the Kouvel-Fisher method, and the Widom scaling relation, differed from the mean-field values. The critical behavior indicates that long-range ferromagnetic order dominates in these Cu-doped samples.

Magnetic nature of the austenite–martensite phase transition and spin glass behaviour in nanostructured Mn2Ni1.6Sn0.4 melt-spun ribbons

Nanocrystalline ribbons of inverse Heusler alloy Mn2Ni1.6Sn0.4 have been synthesised by melt spinning of the arc-melted bulk precursor. The single-phase ribbons crystallize into a cubic structure and exhibit very fine crystallite size of <2 nm. Temperature-dependent magnetization (M–T) measurements reveal ferromagnetic–austenite (FM-A)–antiferromagnetic–martensite (AFM-M) phase transition that begins at MS ≈ 249 K and finishes at Mf ≈ 224 K. During warming, the reverse AFM-M to FM-A transitions begins at As ≈ 240 K and finishes at Af ≈ 261 K. A re-entrant FM transition is observed in the M-phase at \(T_{\text{CM}}\) ≈ 145 K. These transitions are also confirmed by temperature-dependent resistivity (ρ–T) measurements. The hysteretic behaviour of M–T and ρ–T in the temperature regime spanned by the A-M transition is a manifestation of the first-order phase transition. M–T and ρ–T data also provide unambiguous evidence in favour of spin glass at \(T < T_{\text{CM}}\). The scaling of the glass freezing temperature (Tf) with frequency, extracted from the frequency-dependent AC susceptibility measurements, confirms the existence of canonical spin glass at \(T < T_{\text{CM}}\) ≈ 145 K. The occurrence of canonical spin glass has been explained in terms of the nanostructuring modified interactions between the coexisting FM and AFM correlations in the martensitic phase.

Anomalous transport properties ofNi2Mn1−xCrxGaHeusler alloys at the martensite-austenite phase transition

The martensite-austenite phase transition in a series of $\mathrm{N}{\mathrm{i}}_{2}\mathrm{M}{\mathrm{n}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{r}}_{x}\mathrm{Ga}$ Heusler alloys has been investigated by x-ray diffraction, dc magnetization, and electrical resistivity measurements. With increasing Cr concentration, the martensitic phase transformation shifts to higher temperature while the ferromagnetic transition shifts to lower temperature. For $xl0.5$, the martensitic transformation occurs in a ferromagnetic state, while for $xg0.5$, the transition occurs in a paramagnetic state. The Cr doping results in a reconstruction of the electronic structure, particularly, near the Fermi level, which is indicated in the resistivity data where a systematic jumplike anomaly is observed in the vicinity of the martensite-austenite phase transformation. With increasing Cr concentration, the magnitude of the jump in resistivity changes dramatically from less than $1%$ to nearly $18%$ The results are discussed considering the fundamental interactions in Heusler alloys.

Atomistic simulation of martensite-austenite phase transition in nanoscale nickel-titanium crystals

Shape-memory (SM) alloys can, after initial inelastic deformation, reconstruct their pristine lattice structure upon heating. The underlying phenomenon is the structural solid-solid phase transition from low-temperature lower-symmetry martensite to the high-temperature higher-symmetry austenite. Conventional nickel-titanium (NiTi) with near-equiatomic concentration already possesses an eminent importance for many applications, whereas the nanostructured equivalent can exhibit yet enhanced thermomechanical properties. However, no plausible microscopic theory of the SM effect in NiTi exists, especially for nanoscale systems. We investigate the thermally induced martensite-austenite phase transition in free equiatomic nanocrystals, comprising up to approximately 40 000 atoms, by means of molecular-dynamics simulations (MD) using a classical Gupta-type many-body scheme. Thereby we complement and extend a previously published study [D. Mutter, P. Nielaba, Eur. Phys. J. B 84, 109 (2011)]. The structural transition, revealing features of a first-order phase transition, is demonstrated. It is contrasted with the melting phase transition, a quantum solid model and bulk experimental findings. Moreover, a nucleation-growth process is observed as well as the irreversibility of the transition upon cooling.

Thermal and adhesion properties of bioinert layers on a titanium nickelide surface

The results of determination of thermal and adhesive stability of bioinert layers formed by plasma electrolytic oxidation on the surface of titanium nickelide are presented. It is established that the surface processing almost does not affect the martensite-austenite phase transition, which is responsible for the shape memory effect.

Magnetic, magnetocaloric and critical properties of Ni50−xCuxMn37Sn13 rapidly quenched ribbons

Magnetic, magnetocaloric and critical properties of Ni50−xCuxMn37Sn13 (x=0, 1, 2, 4 and 8) rapidly quenched ribbons have been studied. The substitution of Cu for Ni clearly effects on magnetic transitions, magnetocaloric effects and magnetic orders of these alloy ribbons. With increasing the Cu-concentration, the martensitic–austenitic phase transition shifts to lower temperature, from 265K (for x=0) to 180K (for x=4), and disappears with x=8, while the Curie temperature, TC, is almost unchanged. Both the conventional and inverse magnetocaloric effects are observed. The obtained values for the maximum inverse magnetic entropy changes, |ΔSm|max, of the ribbons are relatively large, 5.6Jkg−1K−1 (for x=0) and 5.4Jkg−1K−1 (for x=4) with the external magnetic field change ΔH=12kOe. The critical parameters (TC, β, γ and δ) of the ribbons are determined from the static magnetic data at the second order ferromagnetic–paramagnetic transition by using both the Arrott–Noakes and Kouvel–Fisher methods. The results reveal that the long-range ferromagnetic order in the alloy is tendentiously dominated by increasing the Cu-concentration.

Magnetic properties and magnetocaloric effect at room temperature of Ni50−x Ag x Mn37Sn13 alloys

In this work, we present a detailed study of the magnetic properties and the magnetocaloric effect at room temperature of Ni50−xAgxMn37Sn13 alloys with x = 1, 2, and 4, which were prepared by using an arc-melting method. Experimental results reveal that a partial replacement of Ag for Ni leads to a decrease in the anti-FM phase in the alloys. In addition, the martensitic-austenitic phase transition shifts towards lower temperature and is broaded. The Curie temperature (TCA) for the austenitic phase also shifts toward to lower temperature, but not by much. The Curie temperature was found to be 308, 305, and 298 K for x = 1, 2, and 4, respectively. The magnetic entropy change (ΔSm) of the samples was calculated by using isothermal magnetization data. Under an applied magnetic field change of 10 kOe, the maximum value of ΔSm (|ΔSmax|) was achieved at around room temperature and did not change much (~0.8 J·kg−1·K−1) with increasing Ag-doping concentration. Particularly, the M2 vs. H/M curves prove that all the samples exhibited a second-order magnetic phase transition. Based on Landau’s phase-transition theory and careful analyses of the magnetic data around the TCA, we have determined the critical parameters β, γ, δ, and TC. The results show that the β values are located between those expected for the 3D-Heisenberg model (β = 0.365) and mean-field theory (β = 0.5). Such a result proves the coexistence of short-range and long-range ferromagnetic interactions in Ni50−xAgxMn37Sn13 alloys. The nature of the changes in the critical parameters and the |ΔSmax| is thoroughly discussed by means of structural analyses.

IR Thermography and Resistivity Investigations on Ni-Ti Shape Memory Alloy

The shape recovery efficiency of Ni-Ti shape memory springs has been investigated upon the application up to 6 X 105 thermo-activation cycles. The hysteretic behaviour of the Martensitic-Austenitic phase transition has been characterized by resistivity measurements and infrared thermography. A loss in the recovery efficiency of the original shape has been observed and has been ascribed to functional fatigue leading to the formation of the R phase upon sample heating. Nevertheless, one way shape memory effect was found to exhibit an asymptotic stable behaviour which makes possible the realization of Ni-Ti actuators able to operate for a relative large number of activation cycles.

Free energies of austenite and martensite Fe–C alloys: an atomistic study

We investigate the influence of C interstitials on the phase stability of Fe–C crystals. We employ the Meyer–Entel interatomic interaction potential which is able to reproduce the austenite-martensite phase transition for pure Fe, and supplement it by a simple pairwise Fe–C interaction potential. Using two different thermodynamic methods, we calculate the free energies of the martensite and austenite phases. We find that C destabilizes the ground-state bcc phase. The decrease in the equilibrium transformation temperature with increasing C content parallels the one found in the experiment. This destabilization is found even if C is added for a potential in which only the bcc phase is stable until the melting point; here, for sufficiently high C addition, a stable fcc phase is established in the phase diagram.

Scaling of the isothermal entropy change and magnetoresistance in Ni-Mn-In based off-stoichiometric Heusler alloys

We show that for identical changes in magnetic field, the temperature dependence of the change in isothermal entropy across the martensite-austenite phase transition in different Ni-Mn-In based off-stoichiometric Heusler alloys scales to a single curve. The temperature dependence of magnetoresistance across the same martensite-austenite phase transition in these alloys also scales to follow a similar curve. The temperatures corresponding to the peak value of the isothermal entropy change and the peak magnetoresistance for a particular applied magnetic field are correlated with distinct features observed in the magnetization vs. temperature and resistivity vs. temperature curves respectively of these alloys (in the same magnetic field). These findings can be utilized in estimating the useful temperature regime for the isothermal entropy change and magnetoresistance of Ni-Mn-In based alloys with newer compositions, and to predict the magnitude of these functionalities, without performing actual experiments.

Study of the dynamical features of the austenite-martensite phase transition in the Ni50(Mn, 1%Fe)34In16 alloy using scanning Hall probe imaging

We have performed scanning Hall probe imaging experiments to study the martensite to austenite phase transition in the Ni50(Mn, 1%Fe)34In16 alloy as a function of temperature and magnetic field. We observe that the martensite and austenite phase regions are separated by a distinct interface. The relative growth of phase across the phase transition is associated with the movement of this interface. The movement of the interface becomes arrested at low temperature, which leads to the formation of a “magnetic glass” state in the alloy. The dynamics of the martensite to austenite phase transition in the Ni50(Mn, 1%Fe)34In16 alloy is found to be qualitatively different when the transition is field induced than what it is when the same transition is induced by temperature. While both nucleation and growth of the martensite phase is observed during the austenite to martensite phase transition in the alloy during cooling down, the martensite to austenite phase transition during warming up appears to be growth oriented. In contrast, both nucleation and growth of the product phases are observed during the field induced martensite to austenite phase transition both during increasing and decreasing field experiments. The physical reasons behind these different observations are explored.