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Epitaxial Ni–Mn–Ga thin films have promising application potential in micro-electro-mechanical sensing and actuation systems. To date, large abrupt magnetization changes have been observed in some epitaxial Ni–Mn–Ga thin films, but their origin - either from magnetically induced martensite variant reorientation (MIR) or magnetic domain evolution - has been discussed controversially. In the present work, we investigated the evolutions of the magnetic domain and microstructure of a typical epitaxial Ni–Mn–Ga thin film through wide-field magneto-optical Kerr-microscopy. It is demonstrated that the abrupt magnetization changes in the hysteresis loops should be attributed to the magnetic domain evolution instead of the MIR.

The room temperature gas sensors have always been an important research direction of the gas sensor, and the room temperature gas sensors without the assistance of the light is more valuable. The SnO2 nanoparticles were synthesized by hydrothermal method, which showed good formaldehyde sensitivity, had the advantages of low test temperature, only [Formula: see text]C, good formaldehyde selectivity, and especially the good response to formaldehyde at room temperature. The nanostructure and gas-sensing properties were characterized by scanning electron microscopy, EDS mapping, nitrogen physical adsorption, and X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and WS-60B gas-sensing measurement system. Compared with the reported research results, we carefully discuss the physical mechanism of the SnO2 formaldehyde sensor with low operating temperature and good formaldehyde selectivity in this paper.

In this work, the B2 partial disordered structure of the austenitic parent phase, martensitic transformation, elastic and magnetic properties of the Ni8Mn4+xTi4-x (x = 0, 1 and 2) Heusler alloys have been systematically investigated by the first-principles calculations. The preferential atomic occupation of B2 structure is one Ti atom exchange with the nearest neighboring Mn atom from the view of lowest energy principle. This disordered exchange sites (Mn-Ti) and the excess Mn atoms occupying the Ti sites (MnTi) could reduce the nearest Mn-Mn distance, resulting in the antiferromagnetic state in the austenitic and martensitic phases of the alloys. The total magnetic moment of the alloy decreases with the increasing Mn content; it is ascribed to the antiferromagnetic magnetic moments of the excess Mn atoms. When x = 0, the alloy does not undergo martensitic transformation since the austenite has absolute phase stability. The martensitic transformation will occur during cooling process for x = 1 or 2, owing to the energy difference between the austenite and the martensite could provide the driving force for the phase transformation. The elastic properties of the cubic austenitic phase for the Ni2MnTi alloy is calculated, and the results reveal the reason why Ni-Mn-Ti alloy has excellent mechanical properties. The origin of martensitic transformation and magnetic properties was discussed based on the electronic density of states.

Gyrotron, as a most likely practical high-power terahertz (THz) radiation source, has been widely applied to THz dynamic nuclear polarization-enhanced nuclear magnetic resonance (DNP-NMR) spectroscopy. In this article, an iris cavity with high-quality factor is theoretically designed for a frequency-tunable THz gyrotron, which could be tuned at three frequency regimes: 140, 250, and 263 GHz, respectively. Based on the self-developed nonlinear code, the beam wave interactions in the designed cavity are studied in detail when the corresponding high-order axial modes (HOAMs) are ${\mathrm {TE}}_{-\mathrm {6.1.q}}$ , ${\mathrm {TE}}_{\mathrm {0.4.}\mathrm {q}^{\prime }}$ , and ${\mathrm {TE}}_{\mathrm {8.2.q}''}$ . By tuning the applied magnetic field under the condition that the beam voltage U0 is 20 kV and beam current I0 is 0.10 A, the output power and frequency tuning ranges could achieve 0.75 kW and 1.15 GHz, 0.63 kW and 3.10 GHz, and 0.59 kW and 2.54 GHz. Meanwhile the calculation results are compared with the 3-D particle software CST, which have confirmed that the frequency and power tuning ranges of ${{\mathrm {TE}}}_{-\mathrm {6.1.q}}$ , ${\mathrm {TE}}_{\mathrm {0.4.q}'}$ , and ${\mathrm {TE}}_{\mathrm {8.2.q''}}$ could reach 0.46 kW and 1.07 GHz, 0.37 kW and 2.24 GHz, and 0.34 kW and 1.96 GHz. These results could be beneficial for the development of frequency-tunable gyrotron toward some up-and-coming novel THz applications.

Size effect is a typical characteristic of micro-/nano-materials, which can contribute to a variety of size-dependent behaviors, phenomena, and properties, such as stiffness softening, deformation springback, etc. The intrinsic causes of size effects are micro-structural properties of materials, and the sensitivity of microstructural properties of materials is closely related to the smallest structural unit of the crystal, crystal defects and geometric dimensions, and is heavily influenced by the material’s field conditions. The modeling method based on non-local theory and gradient theory in the model is not only consistent with experimental and molecular dynamics simulation results, but also provides a solid explanation for the size effect underlying ‘softening’ and ‘hardening’ behaviors. Taking this as a basic point, this paper further considers the real working environment of materials, and systematically reviews the static and dynamic mechanical behavior cases of various nano-structures, mainly involving bulking, vibration and wave propagation of micro-beams and plates under different theories. A description and discussion of the differences in mechanical properties resulting from size effects under various theoretical frameworks and three key bottleneck problems are provided: the selection of kernel functions, the determination of size parameters, and the physical meaning of boundary conditions at higher orders. A summary is provided of the possible avenues and potentials for size effect models in future research. Many studies have shown that size parameters have a significant impact on the mechanical behavior of micro-/nano-structures, and these effects will increase as the size of the structure decreases. Nevertheless, different theories have varying scopes of application and size effects, and further research is needed to develop a unified size-dependent theory with universal applicability. A major focus of this paper is on the size effect of micro-/nano-structures, as well as provides the necessary data support to resolve the bottleneck problem associated with the size effect in the processing and manufacturing industries, and realizes the design and optimization of micro-scale parts based on their size.

Composition dependence of martensitic transformations as well as the magnetic properties for the Ni2Mn1+xIn1-x (0.25 ≤ x ≤ 0.58) alloys were investigated by using the first-principles calculations. Key results demonstrate that the stability of parent austenite (A) decreases gradually with increasing Mn content whilst it is opposite for the martensitic phase. This causes the total energy difference between the austenite and martensite phases increscent with increasing Mn contents. When x = 0.33, the martensite transformation during cooling is PA→FA→NM. When x ≥ 0.42, an intermartensitic transformation occurs from modulated 6 M martensite to non-modulated (NM) martensite with the martensite transformation sequence of PA→FA→6M→NM. The martensitic transformation from austenite to martensite accompanies the transition from ferromagnetic to ferrimagnetic state. This is a typical magneto-structural coupling transformation. The analysis of the density of states demonstrates that the Ni 3d state plays an important role in the phase stability.

Enhanced elastocaloric properties in a directionally solidified Ni55Mn18Ga26Ti1 alloy were achieved by combining composition tuning and microstructural control. Owing to the introduction of Ti and the microstructural feature with coarse columnar grains and strong A preferred orientation, the thermal hysteresis and the stress hysteresis were successfully reduced to 4K and 16MPa, respectively. Large adiabatic temperature change of −6.2K was obtained on removing a low stress of 120MPa, resulting in the specific adiabatic temperature change of 51.7K/GPa. Moreover, the alloy demonstrated enhanced cyclability of elastocaloric effect up to 497 loading/unloading cycles and high coefficient of performance value of 25.6.

Selective control of the key parameters of the cold atmospheric plasmas (CAPs) is crucial for diverse applications ranging from materials processing, clinical medicine to clean energy generation. In particular, the low gas temperature (T g) and high electron number density (n e) are both critical for obtaining high treatment efficiency of heat-sensitive materials, yet are challenging to achieve because of the very frequent species collision nature in CAPs. In this paper, selective control of T g and n e in a helium CAP driven by a radio-frequency power supply and operated in an open environment is achieved successfully for the first time numerically and experimentally with the quasi-independent variation windows from −33.7 °C to 49.5 °C (i.e. 239.3 to 322.5 K) for T g and from 2.7 × 1016 to 6.3 × 1016 m−3 for n e. This result has expanded the key CAP parameter windows significantly into a previously unachievable domain. The further theoretical analysis of the energy transfer and balance based on the ‘energy tree’ concept and numerical modeling reveals the unique non-equilibrium energy transfer channel allowing selective control of T g and n e. This energy transfer channel is enabled by the two ‘valves’, one for controlling the energy deposition from the external circuit to the discharge cell (valve 1), and another one for controlling the energy exchange between the discharge cell and the environment (valve 2). Our conceptual approach and proof-of-principle demonstration open a new way for the active and selective control of the key CAP parameters, which will be quite important for designing CAP sources with specific requirements and for advancing or even creating new CAP applications in the future.

International audience; Ni–Mn-based shape memory alloy is a promising candidate as the solid-state elastocaloric refrigerant in the micro- or nano-refrigeration fields owing to the required small driving force. In this letter, we report a multielement alloying strategy, i.e., the co-substitution of non-magnetic element and boron for Mn, to improve the elastocaloric refrigeration efficiency and mechanical properties simultaneously. Under Cu and B co-substitution, a large adiabatic temperature change of –12.8 K and a giant specific adiabatic temperature change of 41.0 K/GPa were obtained in the directionally solidified Ni50(Mn31.7Cu2.5B0.3)In15.5 alloy. The proposed alloying manner is also favorable to enhance fracture resistance and cyclability.

In this paper, a random forest regression (RFR) is proposed to reconstruct the statistical characteristics of electric fields in perforated enclosures. The power balance method and a diffusion equation–based model have been applied to the analysis of such problems; however, they are unable to account for the statistical nonisotropy problem. To solve it, RFR is used to predict the variances of six basic electric fields, the real and imaginary parts of the three rectangular electric field components, in perforated enclosures under external excitation. Using the predicted variances, the probability density function to represent each basic electric field can be generated as they are assumed to obey normal distribution with zero mean value. Then the statistical characteristics of other electric fields can be calculated by an analytical method and Monte Carlo method. Using the proposed method relies on RFR, the overall statistical characteristics of electric fields in perforated enclosures with the electric dimensions less than ten times the wavelength can be accurately reconstructed. Using the predicted statistics, the practical electromagnetic compatibility problem, such as global shielding effectiveness of a perforated enclosure, can be evaluated in seconds.

Poisson’s ratio is one of the fundamental features of materials, reflecting the transverse strain response to the applied certain axial strain. The materials with a negative Poisson’s ratio, also known as auxetic materials, are rare in nature and attract lots of research interest because of their unusual mechanical behavior and extensive applications in mechanical nanodevices. Here, we proposed and studied a novel hyperbolic two-dimensional graphene-like structure (GLS) showing a negative Poisson’s ratio behavior by first-principles calculation. The thermodynamic, dynamic, lattice dynamic, and mechanical stabilities of the GLS were carefully studied. In addition, we also explored the electronic structure, mechanical characteristics, and optical-electronic characteristics. The GLS not only displays a negative Poisson’s ratio in certain directions but also shows low-gap semiconductor characteristics and superior electronic conductivity. It is a potential sunscreen material because of the outstanding reflection and absorption for ultraviolet and infrared light.

Microwave devices based on high-power magnetrons are currently used widely and there is a strong demand for phase-controlled magnetrons. In this work, the performance of a 20-kW $S$ -band continuous-wave magnetron with varied anode voltage ripple is studied. The anode voltage ripple is introduced to an equivalent model of the magnetron to evaluate the system’s performance theoretically. The effects of the anode voltage ripple and the injection parameters on the magnetron’s output are thus analyzed numerically. Furthermore, experiments are performed while the anode voltage ripple is varied from 4.2% to 0.6% using a shunt capacitance-adjustable ripple filter module. A nearly tripled locking bandwidth is observed under a constant injection ratio at 0.1 with decreasing ripple. The ripple-suppressed system pulls its sideband energy to the locking frequency and thus achieves a spectral intensity increment of 0.9 dB, phase noise reduction of 13 dB at an offset of 100 kHz, and phase jitter convergence from ±1.8° to ±0.9°. The experimental features validate the results obtained from the theoretical analyses. The results of this investigation also provide guidance for future industrial applications of phase-locked magnetron arrays.

The martensitic transformation, kinetics, elastic and magnetic properties of the Ni2-xMn1.5In0.5Cox (x = 0-0.33) ferromagnetic shape memory alloys were investigated experimentally and theoretically by first-principles calculations. First-principles calculations show that Co directly occupies the site of Ni sublattice, and Co atoms prefer to distribute evenly in the structure. The optimized lattice constants are consistent with the experimental results. The martensitic transformation paths are as follows: PA ↔ FA ↔ 6 MFIM ↔ NMFIM when 0 ≤ x

BaTiO3/LaNiO3 (BTO/LNO) ferroelectric superlattices with different stacking periods have been prepared by pulsed laser deposition (PLD). Compared to the pure BTO films, the BTO/LNO superlattices have significantly enhanced ferroelectric and dielectric properties. This is because, in addition to the strain effect, the accumulated oxygen vacancies in each ultra-thin LNO layer can change the depolarization field and reduce the leakage current in the superlattices. The results indicate that the use of ultra-thin metallic oxide layers as the constituent material of the ferroelectric superlattices is a feasible and effective way to improve the properties of superlattices.

Pure phase polycrystalline BiFeO₃ film was deposited onto FTO substrate by RF magnetron sputtering method. SEM result shows that BiFeO₃ film has the obvious porosity and large clusters which lead to the poor ferroelectric and photovoltaic properties in FTO/BiFeO₃/Ag device. However, these properties are improved in p-i-n structured FTO/TiO₂/BiFeO₃/HTM/Ag device by incorporating the electron and hole transport materials. The hysteresis loop measurement demonstrates the excellent ferroelectric property with large remnant polarization (2Pr = 180 μC/cm²) and low leakage current. The J-V curve shows the short-circuit current density is dozens of times larger than that of FTO/BiFeO₃/Ag device. Moreover, the photovoltaic output depends on the poling field where the positive poling improves the short-circuit current density to -85 μA/cm₂ and the negative poling reduces both the photocurrent and photovoltage. It is believed that the ferroelectric polarization plays a dominant role in the photovoltaic effect.

International audience; Thermo-mechanical treatment is an effective way to tune the microstructure and enhance the output strain of NiMn-based magnetic shape memory alloys through field driven variant reorientation or structural transformation. Comprehensive knowledge on the microstructural feature and related transformation crystallography is of great importance for the microstructure control and property optimization. In this work, we demonstrate the crossing twin of seven-layered modulated (7 M) martensite assembled in herringbone shape induced by thermo-mechanical treatment in a directionally solidified Ni50Mn30Ga20 alloy. Based on the electron backscatter diffraction (EBSD) measurements, it is found that the crossing twin is composed of four 7 M martensite variants with two mutually crossing systems of twin, i.e., type I twin and compound twin. The type I twin in the crossing twin, being with {1 –2 10}7 M as the twinning plane, is quite different from that of the self-accommodated martensite (i.e., {1 –2 –10}7 M as the twinning plane). A novel transformation orientation relationship between austenite and 7 M martensite in crossing twin is resolved to be {1 0 1}A//{1 –2 10}7 M and A//7 M, in contrast to that of self-accommodated case, i.e., {1 0 1}A//{1 –2 –10}7 M and A//7 M. By using the experimentally determined orientation relationship between two phases to construct the deformation gradient matrix, the underlying mechanism for the selection of twinning system is further discussed.

A polycrystalline BiFeO₃ film was deposited on ITO substrate by RF magnetron sputtering method. Small crystallite size and compact structure are obtained for BiFeO₃ film which has the excellent ferroelectric properties. The measured photovoltaic response reveals an open-circuit voltage of ~0.52 V and a short-circuit current density of ~10 μA/cm² under the illumination of 100 mW/cm² irradiance. Moreover, a tunable photovoltaic effect with light illumination is observed under different voltage sweep mode. High initial sweep voltage can enhance the photovoltaic effect largely, however, the photovoltaic response decreases with the increase of voltage sweep interval. The results indicate the ferroelectric polarization plays an important role in the photovoltaic effect.

We report on flash sintering using a contactless approach. The process is based on dielectric barrier discharge atmospheric cold plasma which allows flash sintering without external preheating. The evenly spread cold plasma plume contributed to homogenous densification of zirconia samples, instead arc discharge resulted in un-sintered and cracked material. Final density and grain size could be controlled by adjusting current and discharge time. A 7 mm diameter disc was sintered up to 99% in 30 s by passing a current of 15 mA (0.39 mA/mm2). The proposed technique is industrially scalable and offers a reliable replacement to platinum electrodes.

Modification of a convective internal boundary layer (IBL) by spanwise motion of a warm surface is investigated by imposing different surface moving speeds in the present study. Our analysis shows that the spanwise surface motion reduces the Reynolds shear stress right after the increase in the surface temperature in the convective IBL. The maximum decreasing rate of the Reynolds shear stress is found to be approximately 75% at the largest moving speed of the warm surface considered in the manuscript. Due to the reduction of the Reynolds shear stress, the vertical momentum transport is fundamentally altered, and the mean flow accelerates immediately after the increase in the surface temperature. By scrutinizing the instantaneous and conditional averaged flow fields as well as the pre-multiplied energy spectra, we have attributed the reduction of the Reynolds shear stress to the suppression of the near-surface velocity streaks and quasi-streamwise vortices, and the delayed growth of the convective structures, such as thermal plumes. Our investigation suggests that the developments of the convective IBL can be influenced by a strong spanwise motion of the warm surface, which should be taken into consideration in the prediction model for practical applications.

Conventional immersed boundary methods (IBMs) have greatly simplified the boundary condition treatment by interpreting boundaries as forces in the source terms of governing equations. In conventional IBMs, uniform meshes of very high resolution must be applied near the immersed boundary to treat the solid–fluid interface. However, this can induce a high computational cost for simulating flows with large moving boundary domains, where everywhere along the trajectory of the moving object must be refined isotropically. In the worst scenario, a global refinement is required when the object is moving arbitrarily in the entire computational domain. In this work, an overset boundary condition-enforced immersed boundary method (overset BC-enforced IBM) is proposed to simulate incompressible flows with large moving boundary domains efficiently. In the proposed overset BC-enforced IBM, a locally refined uniform mesh is applied and fixed on the moving object to account for the local motions, e.g., the rotation and deformation of the object, while the global motion of the object is handled by embedding the locally refined mesh in a coarser background mesh. Both the local mesh and the global background mesh can be generated automatically using the Cartesian approach to avoid the cumbersome boundary treatment. Since the mesh refinement is local, considerable computational savings can be achieved. The overset BC-enforced IBM is combined with the lattice Boltzmann flux solver to simulate various fluid–structure interaction problems with rigid and deformable boundaries.

The effects of Co doping on the phase stability, martensite transformation and magnetic properties of Ni 24- x Mn 17 In 7 Co x ( x = 0–5) ferromagnetic shape memory alloy were systematically investigated by the first-principles calculations. Co atom prefers to occupy the Ni sublattice. Co doping increases equilibrium lattice constant of austenite and decreases phase stability of austenite, 6 M and NM martensites. When 0 ≤ x x ≥ 2, the corresponding martensite transformation is PA→FA→NM. The martensitic transformation from austenite to martensite (6 M and NM) accompanies the ferromagnetic to ferrimagnetic transition in the Co content 0 ≤ x ≤ 2. However, the ferromagnetic state is popular in the whole martensitic transformation process for x > 2. The origin of magnetic properties and magnetostructure transformation were discussed based on electronic density of states.

Well dispersed CeO₂ nanoparticles are prepared by azeotropic co-precipitation method. (Ba0.96Ca0.04)(Ti0.90Sn0.10)O₃ lead-free piezoelectric ceramics doped with nano-CeO₂ (x =0 mol%, 0.03 mol%, and 0.07 mol%) and micro-CeO₂ (x = 0.03 mol%) are prepared at 1430 °C for 2 h by the conventional solid state sintering method. XRD diffraction indicates that all components have typical perovskite structure. Both doping of nano-CeO₂ and micro-CeO₂ can inhibit grain growth. And the average grain size decreased apparently with the increase of nano-CeO₂ amount. All the samples exhibit typical diffuse phase transition behavior. The optimized electrical performances are obtained at x = 0.03 mol% with d33 = 512 pC/N, kp = 41.5%, and Pr = 14.00 μC/cm².

Shielding effectiveness (SE) of metallic structures with thin slots can be analyzed by using finite-difference time domain (FDTD) method. However, the arbitrarily shaped thin slots make the calculation be unbearable or even worse. To improve the computational efficiency, contour path (CP) algorithm is thus extended to be applied to the calculation of complex thin slots using FDTD. An equivalent model is proposed to simplify the CP-FDTD calculation for thin slots with complex penetrating paths formed by overlapped joints or flush-mounted aperture panels. It is validated by the good accordance of SE obtained using conventional fine-cell FDTD for different kind of slots with various penetrating paths. The SE prediction accuracy in terms of incident wave and the ratio of slot width to Yee's cell size are investigated. The physical measurement of SE of a metallic enclosure with thin slots is conducted and its results are in a good agreement with that obtained by using extended CP-FDTD.

In this paper, the electromagnetic environment (EME) characteristics on Wangjiang campus of Sichuan University, a typical densely populated urban area, are measured and analyzed. According to the people's daily routine, the EME measurements are performed during daytime, nighttime, weekday, and weekend, respectively. By measuring the electric field (E-field) values along the main roads on the campus, the maps of E-field spatial distribution are obtained. Results indicate that the EME on the campus is relatively stable. The probability density functions of three orthogonal components of E-field are all lognormal distribution and very similar to each other due to depolarization phenomenon and polarization rotation of multipath propagation. Moreover, the total E-field is also lognormal distribution because of the high linear correlation between the components. In addition, E-field were also measured over time on three different sites, playground, laboratory, and student dormitory, in order to get time-varying characteristics of the EME. Results suggest how the people's activities influence on EME. All measurements on Wangjiang campus show that the maximum E-field value is far below the regulatory exposure limits proposed by the International Commission on Non-Ionizing Radiation Protection.

Increased interest in thermo-electro-elastic during the last decades can be assigned to the fact that the study of thermo-electro-elastic mechanical coupled behavior in smart structure. For instance, the coupled thermo-electro-elastic dynamic factors are meaningful in designing process of some sensors and energy harvesting products. This paper presents the steady-state analytical solutions for the coupled thermo-electro-elastic forced vibrations of piezoelectric laminated beams. Two types of damping, material damping and air damping, are introduced to the coupled vibration system. Based on Erturk and Inman’ work, a novel electric circuit model is developed. Thus, for this model, the electric factor is introduced into the classical coupled thermoplastic vibration problems for the piezoelectric laminated beams. Using the decoupled method solve the three fields of coupling problems by developing a generalized form of Green's functions. The interactions between the thermal and electric factors are obtained analytically. The convergence of the present solutions is firstly verified in the numerical section followed by the FEM results used to validate the achieved solutions. From the sample numerical calculations, it is seen that the two-dimensional temperature field presents different distributions for different electric conditions. Moreover, the optimum heat transfer coefficient is furnished for the energy harvesting problem of the laminated beam.

In the interaction representation, a gauge independent investigation has been performed on the system of two dimensional rarefied charge gas, which is subjected to a perpendicular strong magnetic field and an in-plane weak electric field that is switched on when t ≥ 0. The present results show that besides a Hall direct current, there are also transverse and longitudinal alternating currents with the same frequency. The alternating current frequency corresponding to the cyclotron oscillation, can be further used to measure the effective mass of carriers in semiconductors with high accuracy.

Molybdenum oxide (MoOx) thin films were prepared by pulse DC sputtering using a molybdenum target and their optical and electrochromic properties were investigated. These MoOx thin films were reactively sputter-deposited at various oxygen flow rates. The effects of the oxygen flow rate on the growth and microstructure of the molybdenum oxide films were examined using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The optical density and modulation of the MoOx films were analyzed using a UV/VIS spectrophotometer (UV–visible). Electrochromic tests were conducted using an electrochemical analyzer. Experimental results reveal that the electrochromic properties depended strongly on the crystalline phase, thickness, chemical composition and microstructure, which were controlled by varying the oxygen flow rate.

The first-order inter-martensitic transformation induced by temperature change or external stress is frequently observed in Ni-Mn-Ga alloys. Here, the inter-martensitic transformation is exploited to strengthen the elastocaloric effect. Through the stress-induced two-step structural transformation, i.e., martensitic and inter-martensitic transformation, giant adiabatic temperature change up to −10.7 K is obtained in a directionally solidified Ni55Mn18Ga27 polycrystalline alloy with 〈001〉A preferred orientation, representing the highest value so far in Ni-Mn-Ga alloys. It is demonstrated that microstructure texturing together with introduction of inter-martensitic transformation could be an effective route to improve the elastocaloric properties in polycrystalline NiMn-based alloys.

Bake-partitioning, a process integrating paint-baking of car-body assembling to induce carbon partitioning into austenite, has been proposed for enhancing the ductility of press-hardening steels. Carbon is estimated to diffuse a maximum distance of 2.7 nm in austenite at 170 °C for 20 min. Austenite films with a thickness of approximately 5 nm are therefore desired for sufficient bake-partitioning. This was realised by the ultra-fine prior austenite grain due to 7 wt% of manganese addition combined with vanadium carbide precipitation. The novel alloy exhibits 1800 MPa ultimate tensile strength combined with 16% elongation, which has never been achieved in press-hardening steels.

The complete martensitic transformation sequence and magnetic properties of the non-stoichiometric Ni2Mn1.2Ga0.8 alloy have been revealed by the first-principles calculations. The calculated martensitic transformation sequence of the Ni2Mn1.2Ga0.8 alloy during cooling is Paramagnetic Austenite (PA) → Ferromagnetic Austenite (FA) → 7M → NM, which is consistent with the experimental observations. When the cubic FA phase transforms to a 7M or NM martensitic phase, a significant reduction of the down-spin total density of states occurred at the Fermi level. This makes the martensitic phase more stable than the FA phase at low temperature.