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Phase transition of Ni_(55-x)Co_(x)Mn_(20)Ga_(25)(8.5≤x≤11.0)alloys with different compositions and magnetic fields

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Rare Metals 2023年第2期42卷 572-578页

作者： Xiao Wang Jing-Min Wang Hui Hua cheng-bao jiang Key Laboratory of Aerospace Materials and Performance(Ministry of Education) School of Materials Science and EngineeringBeihang UniversityBeijing100191China

Studies on Co-doped Ni–Mn–Ga ferromagnetic shape memory alloys(FSMAs)have been quite active topics in recent *** previous reports where the amount of Co doping was generally less than 8 at%,in this work Ni_(55-x)Co_(x)Mn_(20)Ga_(25)(8.5≤x≤11.0)alloys were studied with high Co *** effects of both composition and magnetic field on phase transitions were *** the increase in substitution of Co for Ni,the magnetic transition temperatures increase gradually but the martensitic transformation temperature decreases quite *** particular,the average decrease in the martensitic transformation temperatures is up to 100 K which is nearly twice that in the case of Co content of less than 8 at%.Further,under an applied magnetic field ranging from 0.03 to 0.60 T,abnormal stabilization of a martensite phase with lower magnetization was *** entropy change of 1.6 J·kg^(−1)·K^(−1)was induced at the martensitic transformation of Ni46.5Co8.5Mn20Ga25 alloy by an applied field of 1 *** magnetic contributions,including the magnetocrystalline anisotropy and the Zeeman energy,to the thermodynamics of the martensitic transformation are considered to understand the observed unusual *** work results in new insights into the understanding of Co-doped Ni–Mn-based ferromagnetic shape memory alloys.

关键词： Ni-Mn-Ga Ferromagnetic shape memory alloys Martensitic transformation Magnetic properties Magnetocaloric effect

Influence of cooling rate on magneto-structural transition and magnetocaloric effect of Ni_(30)Cu)8Co_(12)Mn_(37)Ga_(13) alloy

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Journal of Iron and Steel Research International 2017年第7期24卷 711-717页

作者： Zhu-jun jiang Yu-ye Wu Jing-min Wang cheng-bao jiang School of Materials Science and Engineering Beihang University School of Physics and Nuclear Energy Engineering Beihang University

The influence of heat treatment with different cooling rates on phase transition behaviors and magnetocaloric effect is systematically *** in atomic order is induced by changing cooling rates,where ordered phase is obtained in the furnace cooled（FC）sample while disordered phase is reserved in the water quenched（WQ）*** coupled magneto-structural transition is detected in both samples but the characteristic temperature significantly shifts to lower temperatures with increasing atomic *** magnetic entropy change（ΔS_（mag））derived from magnetic field induced martensitic transformation is confirmed for both samples,and can be remarkably enhanced by the atomic *** largestΔS_（mag） of 20.9J/（kg·K）is obtained at 307.5Kunder 5Tin the FC sample.

关键词： Ferromagnetic shape memory alloy Heat treatment Martensitic transformation Magnetocaloric effect Cooling rate Magneto-structural transition

A linear elastic Ni_(50)Mn_(25)Ga_9Cu_(16) martensitic alloy

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Rare Metals 2013年第1期32卷 29-32页

作者： Cong-Wei Wang Jing-Min Wang cheng-bao jiang Key Laboratory of Aerospace Materials and Performance (Ministry of Education) School of Materials Science and Engineering Beiing University of Aeronautics and Astronautics

The linear elasticity was studied in a martens- tic alloy NisoMn25Ga9Cu16. A 0.4 % linear elastic strain is btained in the polycrystalline sample under compressive stress of 745 MPa. The elastic modulus is 186 GPa. The obtained linear elastic strain and elastic modulus are much higher than that of ternary Ni-Mn-Ga martensitic alloys.~.bstract The linear elasticity was studied in a martens- tic alloy NisoMn25Ga9Cu16. A 0.4 % linear elastic strain is ~btained in the polycrystalline sample under compressive stress of 745 MPa. The elastic modulus is 186 GPa. The obtained linear elastic strain and elastic modulus are much higher than that of ternary Ni-Mn-Ga martensitic alloys.

关键词： Ni-Mn-Ga Linear elasticity Elasticmodulus Martensite

Correlation of microstructure and magnetic properties in Sm(Co_(bal)Fe_(0.1)Cu_(0.1)Zr_(0.033))_(6.93) magnets solution-treated at different temperatures

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Rare Metals 2019年第1期38卷 20-28页

作者： cheng Xu Hui Wang Tian-Li Zhang Alexander Popov Raghavan Gopalan cheng-bao jiang School of Materials Science and Engineering Beihang University M.N. Miheev Institute of Metal Physics Ural Branch of Russian Academy of Sciences International Advanced Research Centre for Powder Metallurgy and New Materials(ARCI) IITM Research Park

The correlation of microstructure and magnetic properties in Sm(Co_(bal)Fe_(0.1)Cu_(0.1)Zr_(0.033))_(6.93) magnets solution-treated at different temperatures was systematically investigated. It is found that the magnets solution-treated at 1219℃ possess a single 1:7 H phase, exhibiting the homogeneous cellular structure during further aging treatment, leading to the optimum magnetic properties. However, for the magnets solution-treated at 1211 and 1223℃,2:17 H or 1:5 H secondary phase will also form besides 1:7 H main phase, which cannot transform into cellular structure,thus deteriorating the magnetic properties greatly. The irreversible magnetization investigations with recoil loops also propose a non-uniform pinning in the magnets induced by the secondary precipitates. At proper solution temperature, Zr is supposed to occupy the Fe-Fe dumbbell sites in the form of Zr-vacancy pairs, leading to the minimum c/a ratio and thus stabilizing the 1:7 H phase. Finally,Sm(Co_(bal)Fe_(0.1)Cu_(0.1)Zr_(0.033))_(6.93) magnets with the maximum energy product and intrinsic coercivity at 550℃ up to 60.73 kJ·m^(-3) and 553.88 kA·m^(-1) were prepared by powder metallurgy method.

关键词： Sm2Co17 Solution treatment Phase constitution Demagnetization curve squareness

Synthesis of SmCo_5 nanoparticles with small size and high performance by hydrogenation technique

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Rare Metals 2018年第12期37卷 1021-1026页

作者： Zhen-Hui Ma Tian-Li Zhang Hui Wang cheng-bao jiang School of Materials Science and Engineering Beihang University

SmConanoparticles(NPs) have promising applications in high-density magnetic storage and magnetic nanocomposites. In this work, A novel method to yield SmCoparticles with small size and high coercivity was reported. Firstly, SmO-Co NPs with size of 6-15 nm were fabricated by a solvothermal route. Then the agglomerated SmCoparticles were obtained by thermal reduction of the precursor, which show high coercivity of2.0 T at room temperature. At last, the as-synthesized SmCoparticles were further hydrogenated under high hydrogen pressure of 4 MPa at room temperature, where hydrogen absorption process could form small-sized SmCoHparticles due to their lattice expansion and hydrogen desorption process could convert SmCoHNPs into SmCoNPs. The prepared SmCoNPs after hydrogenation, showing well distribution, have a small size of5-20 nm and room temperature coercivity of 1.22 T.

关键词： SmCo_5 Nanoparticles Hydrogenation Coercivity

Chemical synthesis and characterization of SmCo_(5)/Co magnetic nanocomposite particles

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Rare Metals 2021年第5期40卷 1224-1231页

作者： Ying Dong Tian-Li Zhang Hui Wang Xin Liu cheng-bao jiang School of Materials Science and Engineering Beihang UniversityBeijing 100191China

Magnetic nanocomposite material has been widely focused for the potential to become the next generation of magnetic *** this paper,two kinds of chemical coating methods were used to prepare SmCo_(5)/Co nanocomposite particles which were further characterized and *** two methods were carried out by using different materials and at different *** Method I,oleylamine(OAm),oleic acid and Ca(acac)2 were used and the reaction was carried out at the temperature of 300℃.In MethodⅡ,anhydrous isopropanol,polyvinylpyrrolidone(PVP),N_(2)H_(4)·H_(2)O and CoCl_(2)·6 H_(2)O were used and the reaction temperature was~55℃.It was found that by using the two methods,the growth and the crystal structure of the Co nanoparticles(NPs)are *** Method I,epitaxial growth on the surface of SmCo_(5) NPs was observed and the Co NPs were in a facecentered close packing crystal *** in Method II,the coated Co NPs were self-nucleated with a crystal structure of hexagonal close *** MethodⅡwith the addition of surfactant,anisotropic nanocomposite particles were achieved with an enhanced saturated magnetization of 84.2 A·m^(2)·kg^(-1).And the coercivity change of the NPs illustrates that a nonmagnetic interlayer between the hard and soft magnetic phase is beneficial to maintain the coercivity.

关键词： Nanocomposite particles Chemical coating Core/shell Magnetic properties Rare-earth material

Temperature stability of SmCo(2:17) magnets modified by Ni-Cr two-layer coating

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Rare Metals 2019年第3期38卷 238-244页

作者： Saira Bibi Jing-Min Wang M. Faisal Rathore cheng-bao jiang School of Materials Science and Engineering Beihang University National Center of Physics Quaid-e-Azam University

The oxidation resistance behavior of SmCo(2:17)-type high-temperature magnets modified with Ni-Cr two-layer coating was studied. The study depicts the mass gain kinetics and magnetic properties of uncoated and NiCr-modified magnets oxidized at high temperature(500 ℃) in air for 200 h. The oxidation test results illustrate that the mass gain of uncoated magnet is6.95 mg·cm^(-2) which is more than that(0.08 mg·cm^(-2)) of coated magnet after 200 h. For the magnetic properties concerned, there is a great loss for uncoated magnet, while for coated magnet, magnetic properties do not change much. The study of uncoated magnet through X-ray diffraction(XRD) and electron probe microanalysis(EPMA) shows that the invasion of oxygen at high temperature leads to the loss of magnetic properties by changing the microstructure of magnet.

关键词： SmCo(2:17) magnets Surface modification High temperature stability Ni-Cr coating

Chemical synthesis of SmCo5/Co magnetic nanocomposites

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Rare Metals 2019年第4期38卷 306-311页

作者： Run-Bo Lu Zhen-Hui Ma Tian-Li Zhang cheng-bao jiang School of Materials Science and Engineering Beihang University

A three-step chemical synthesis of SmCo5/Co nanocomposites was developed. Firstly, the Co-Sm（OH）3-Ca（OH）2 precursors were prepared by ***, SmCo5 particles were obtained by reductive annealing of the precursors. At last, the SmCo5/Co nanocomposites were achieved by chemical deposition based on SmCo5 particles. The SmCo5/Co nanocomposites contain hard magnetic phase of SmCo5 with about 100 nm in size and soft magnetic phase of Co with about 8 nm in size,exhibiting independent two-phase structure without alloying. Compared to that of single-phase SmCo5 particles, the saturation magnetization of SmCo5/Co nanocomposites is increased by 27.5%. The synthesis provides a new route to fabricate SmCo-based nanocomposites.

关键词： Magnetic nanocomposites SmCo5/Co Three-step chemical synthesis

Hot corrosion of surface-modified Sm_(2)Co_(17) high-temperature magnet with Ni and Ni/Cr bilayer coatings in 75 wt% Na_(2)SO_(4)–NaCl mixture

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Rare Metals 2021年第9期40卷 2494-2500页

作者： Saira Bibi Jing-Min Wang Tariq Mehmood Waheed Qamar Khan cheng-bao jiang Key Laboratory of Aerospace Materials and Performance(Ministry of Education) School of Materials Science and EngineeringBeihang UniversityBeijing 100191China Institute of Advanced Materials Bahauddin Zakariya UniversityMultan 60800Pakistan School of Space and Environment Beihang UniversityBeijing 100191China

Hot corrosion behavior of Sm_(2)(Co, Fe, Cu,Zr)17-type high-temperature magnetic alloy without and with a protective coating of Ni and Ni/Cr bilayer at 500 ℃ in a corrosive mixture of 75 wt% Na_(2)SO_(4)–NaCl for 100 h was reported in this paper. The obtained results of timedependent weight change established the parabolic growth of oxidized surface of bare magnets(8.87 mg·cm^(-2)),which caused a rapid loss of magnetic properties measured both at room and high temperatures(500 ℃). X-ray diffraction(XRD) analysis revealed the growth of oxides for bare magnet and Cr–oxides(Cr_(2) O_(3)), top layer of Ni/Cr bilayer coating, but in the case of single coating, Ni–sulfides formation indicated penetration of sulfur, which is further verified by electron probe microanalysis with energy dispersive spectroscopy(EPMA/EDS) *** showed that bilayer-coated samples(Ni/Cr) performed better than Ni-coated and bare samples.

关键词： Hot corrosion SmCo-based alloys Oxidation Coatings