A systematic investigation of microstructure and crystallography of the multiply twinned structure at the nanometer scale in a Ni
53Mn
25Ga
22 ferromagnetic shape memory alloy (FSMA) was performed. ...Nanoscale internal twins inside the micrometer-scale martensitic lamellae were observed. In each lamella, two nanotwin variants with a compound twinning relationship exist, and the twinning elements are
K
1
=
{
1
1
2
}
,
K
2
=
{
1
1
2
¯
}
,
η
1
=
〈
1
1
1
¯
〉
,
η
2
=
〈
1
1
1
〉
,
P
=
{
1
1
¯
0
}
and
s
=
0.379
. Two types of lamellar interfaces, i.e., interpenetrated interlamellar interface and stepped intralamellar interface, were revealed. The orientation relationships between the nanotwins connected by these two types of interfaces were unambiguously determined, and it was found that the respective orientation relationship between the neighboring nanotwins depends strongly on the adjacency condition at the interfaces. The possible formation mechanisms of the interpenetrated interlamellar interface and stepped intralamellar interface are discussed. These results are useful for property optimization by microstructure control in the FSMAs.
A systematic study of the magnetic properties and both the temperature- and magnetic-field-induced structural transformations in the Ni50−xCoxMn39Sn11 (0⩽x⩽10) multifunctional alloys over a large ...temperature range from 500K down to 10K was performed. It is revealed that, with increasing x, the martensitic transformation temperatures first decrease slowly when 0⩽x⩽4 and then decrease rapidly when 5⩽x⩽8; no martensitic transformation was observed in the alloys with 9⩽x⩽10. The magnetic properties of these alloys are very sensitive to their chemical composition. The austenite in the alloys with 0⩽x⩽4 shows paramagnetic behavior and the martensite exhibits paramagnetic, superparamagnetic (SPM), and superspin glass (SSG) behaviors in different temperature ranges during cooling. In contrast, the austenite in the alloys with 5⩽x⩽8 is paramagnetic above its Curie temperature TC and ferromagnetic below TC, and the martensite shows SPM and SSG behaviors in different temperature ranges. The austenite in the alloys with 9⩽x⩽10, which remains stable down to 10K, shows paramagnetic and ferromagnetic behaviors above and below TC, respectively. The complete phase diagram for the Ni50−xCoxMn39Sn11 (0⩽x⩽10) alloy system, from high temperature down to 10K, is established. A significant magnetic-field-induced decrease of martensitic transformation temperatures and almost fully reversible magnetic-field-induced structural transformation are achieved across a broad temperature range in the alloys with 5⩽x⩽8. These results are important for understanding the composition and temperature-dependent functional properties, as well as their underlying mechanisms, in the Ni–(Co)–Mn–X (X=In, Sn, Sb) multifunctional alloys.
Cyclability of elastocaloric effect is of crucial importance for practical applications of elastocaloric refrigeration which is a promising alternative to the conventional cooling technology based on ...vapor compression. The well-known Ni-Mn-based magnetic shape memory alloys exhibit fascinating multicaloric effects (including elastocaloric, magnetocaloric and barocaloric effects), but they are intrinsically brittle because of weak grain boundary cohesion, which results in poor cyclic stability of elastocaloric effect. Here we demonstrate that microalloying with boron is very effective in enhancing the mechanical properties and cyclic stability of elastocaloric effect in Ni-Mn-In intermetallic magnetic shape memory alloys. The elastocaloric effect of the boron-free Ni51.5Mn33In15.5 alloy degrades rapidly after only ∼20 cycles; in contrast, that of the boron-doped (Ni51.5Mn33In15.5)99.7B0.3 alloy remains stable with almost no degradation for more than 150 cycles. The enhancement of mechanical properties and cyclic stability of elastocaloric effect is mainly attributed to the increase of gain boundary cohesion and grain refinement resulting from microalloying with boron. Furthermore, by virtue of its enhanced mechanical properties, a high adiabatic temperature change up to 6.6 K (under 550 MPa), a large stress-induced entropy change of 20.0 J kg−1 K−1 (under 300 MPa) and a high coefficient of performance of 18 were successfully achieved in the boron-doped (Ni51.5Mn33In15.5)99.7B0.3 alloy showing a working temperature just around room temperature. These advantages make this alloy promising for room-temperature elastocaloric refrigeration. This study is instructive for designing high-performance elastocaloric materials for solid-state mechanocaloric cooling applications.
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The practical applications of magnetocaloric materials for magnetic refrigeration require not only large magnitude but also reversibility, as well as room-temperature operating temperature, of the ...magnetocaloric effect. However, it is a complex problem to simultaneously meet these demands in the Heusler-type Ni-(Co)-Mn-X (X = In, Sn, Sb, Ga) magnetic shape memory alloys which are a promising candidate for magnetocaloric materials, owing to the interdependence of magnetostructural transformation parameters. Here, through synergic tuning of magnetostructural transformation parameters via alloying with Ti in Ni42-xTixCo9Mn39Sn10 alloys, we achieved a large reversible room-temperature magnetocaloric effect. By alloying with a proper amount of Ti, the martensitic transformation temperature was brought down to room temperature and the sensitivity of transformation temperature to magnetic field change was greatly enhanced with the transformation entropy change still remaining a large value, while the thermal hysteresis and the transformation interval only slightly increased. Thus, the field required to induce the complete and reversible transformation was significantly reduced. As a result, a large reversible room-temperature magnetic entropy change ΔSm of 18.7 J kg−1 K−1 under 5 T was achieved in the Ni41Ti1Co9Mn39Sn10 alloy. This is the first report on reversible ΔSm in Ni-Mn-Sn-based Heusler alloys and the ΔSm we achieved represents the highest reversible ΔSm under 5 T reported heretofore in Ni-Mn-based Heusler alloys. Furthermore, the Ni41Ti1Co9Mn39Sn10 alloy shows good compressive properties and stable martensitic transformation during thermal cycling, beneficial for potential magnetocaloric applications. This study is instructive for the development of high-performance magnetocaloric materials for room-temperature magnetic refrigeration.
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Large reversible caloric effects covering a broad temperature region are essential for high-efficiency and environment-friendly solid-state caloric refrigeration that can potentially replace the ...traditional vapor-compression-based cooling technology. Here, we report the simultaneously achieved large reversible magnetocaloric and elastocaloric effects in a Ni43Co6Mn40Sn11 magnetic shape memory alloy. A reversible near-room-temperature magnetic entropy change ΔSm of as high as 19.3 J kg−1 K−1 under 5 T was experimentally obtained and the corresponding adiabatic temperature change ΔTad was estimated to be 7.7 K. Meanwhile, a large reversible elastocaloric effect with a directly measured ΔTad up to 7.1 K was attained. The elastocaloric effect exhibits high cyclic stability with no apparent degradation during 380 cycles of loading and unloading. Furthermore, we propose and demonstrate the utilization of the multicaloric approach under the coupled uniaxial stress and magnetic field to enlarge the refrigeration temperature region of reversible caloric effects. By combining the reversible magnetocaloric and elastocaloric effects and the reversible multicaloric effect under the coupling of uniaxial stress and magnetic field in the hysteresis region, large reversible caloric effects covering a broad temperature region from 257 K to 383 K can be obtained. This study may pave the way for designing advanced caloric materials with cyclically stable and reversible large caloric effects and wide refrigeration temperature region for solid-state refrigeration.
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The micromechanical behavior of high-strength steels with multiple phases was characterized using the in situ high-energy X-ray diffraction technique. For the materials investigated, the {2
0
0} ...lattice strains of the constituent phases (ferrite, bainite and martensite) with similar crystal structures were determined by separating their overlapped diffraction peaks and then examining the respective changes in peak positions during deformation. Based on those experimental data, the anisotropic elastic and plastic properties of the steels were simulated using a self-consistent model for predicting the grain-to-grain and phase-to-phase interactions. The constitutive laws for describing the elastic and plastic behavior of each constituent phase were directly obtained by comparing the predicted lattice strain distributions with the measured ones. The transmission electron microscopy observations of the microstructure development verified the partitioning of plastic strains among different phases. The present investigations provide a fundamental understanding of the stress partitioning of soft and hard phases, and the different work-hardening rates of the multiphase steels.
Ni-Mn-based metamagnetic shape memory alloys have been extensively studied due to their multifunctional properties including magnetocaloric effect (MCE), magnetoresistance effect, and ...magnetic-field-induced strain. However, the large intrinsic thermal hysteresis of these alloys sets a limit on further development for practical applications. Here, with a few atomic percent Al substitution, we greatly reduced the thermal hysteresis and transformation temperature interval while maintaining the large magnetization difference (ΔM) between austenite and martensite. The simultaneous achievement of a large ΔM and low thermal hysteresis leads to a remarkable enhancement in MCE upon Al substitution, and a maximum magnetic entropy change of 31.6 J/kg K is achieved under a field of 5 T in Ni39Co11Mn40Sn8Al2. Furthermore, our in situ high-energy X-ray diffraction experiments show that the Ni39Co11Mn40Sn8Al2 has good geometric compatibility between austenite and martensite, which accounts for the reduced thermal hysteresis in this alloy. This study is instructive for the development of high-performance magnetocaloric materials in the metamagnetic shape memory alloys.
•The thermal hysteresis and transformation temperature interval were greatly reduced with Al substitution.•The simultaneous achievement of a large magnetization difference and low thermal hysteresis.•A large magnetic entropy change of 31.6 J/kg K under 5 T is achieved.•Good geometric compatibility was disclosed by in situ high-energy X-ray diffraction technique.
A detailed study of martensitic transformation crystallography and microstructural characteristics in the Ni
53Mn
25Ga
22 ferromagnetic shape memory alloy (FSMA) was performed by both experimental ...observation and theoretical calculation. It is revealed that there are two microscopically twin-related martensitic variants with a misorientation of ∼82° around the 〈1
1
0〉
M axis in each initial austenite grain. The twin interface plane was determined to be {0.399
0.383
0.833}
M (1.79° away from {1
1
2}
M). The ratio of the amounts of the two variants inherited from one single austenite grain is about 1.70. The prevalent orientation relationship between austenite and martensite was found to be Kurdjumov–Sachs (K–S) relationship with (1
1
1)
A//(1
0
1)
M,
1
1
¯
0
A
/
/
1
1
1
¯
M
. A successful explanation of the crystallographic features during martensitic transformation will shed light on the development of FSMAs with optimal performance.
Exploration of high-performance elastocaloric materials is of great significance to the development of environmentally friendly mechanocaloric cooling technology that could potentially substitute the ...conventional cooling technology based on vapor compression. In the present work, the elastocaloric effect of a polycrystalline Ni43.5Co6.5Mn39Sn11 magnetic shape alloy was investigated mainly by mechanical testing. A large stress-induced entropy change of ~11.1Jkg−1°C−1 under 310MPa was achieved, which corresponds to more than 80% of the maximum attainable value, i.e. the transformation entropy change. Incorporating the advantages of low cost, non-toxicity, easy fabrication, and abundance in constituent elements, this alloy shows promising prospects for solid-state elastocaloric refrigeration applications. This study also provides instructive information for the design of high-performance elastocaloric materials.
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•A large elastocaloric effect was achieved in a Ni-Co-Mn-Sn magnetic shape memory alloy.•The stress-induced entropy change reaches 11J/(kg °C) under 310MPa, which is more than 80% of the maximum attainable value.
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