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Zhenchen Zhong – 1st expert on this subject based on the ideXlab platform

  • Evolution of Microstructure, Magnetic Properties, and Thermal Stabilities of Isotropic Alnico Ribbons
    IEEE Transactions on Magnetics, 2020
    Co-Authors: Sajjad Ur Rehman, Qingzheng Jiang, Zhenchen Zhong


    The magnetic properties of Alnico alloys are highly dependent on the spinodally decomposed nanostructure. In this article, we report the fabrication of Alnico nanoribbons and the effects of various heat treatments on the magnetic properties, spinodal decomposition, microstructure, and temperature stability. It is found that the spinodal decomposition occurs in a wider range of temperatures from 800 °C to 860 °C. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses of the microstructure confirmed that the nanostructure phases develop in a wide temperature range. Aspect ratio of the order of ~20 is obtained by optimizing the heat treatment conditions. Magnetic properties of Hcj = 815 Oe, Br = 6.70 kG, and (BH)max = 1.88 MGOe are obtained after simplified heat treatment. The magnetic properties of the alloys are measured at low (10 K) and at high (800 K) temperature, and it is shown by calculating temperature coefficient of remanence (α) and temperature coefficient of coercivity (β) that Alnico ribbons possess extraordinary temperature stability at low and high temperatures.

  • microstructure and magnetic properties of ndfeb alloys by co doping Alnico elements
    Physics Letters A, 2019
    Co-Authors: Sajjad Ur Rehman, Qingzheng Jiang, Lunke He, Lei Wang, Houdong Xiong, Munan Yang, Zhenchen Zhong


    Abstract Elements of Alnico 8 are added into Nd-Fe-B alloys fabricated by rapid solidification method. It is observed that the magnetic properties at high temperature improved by small addition of Alnico elements. The Curie temperature of the alloys increased from 580 K for standard alloy to 639 K by 20% addition of Alnico 8 elements. The spin reorientation temperature decreased from 133 K to 104 K. The TEM analysis showed that elements of Alnico 8 refine the microstructure of Nd-Fe-B ribbons. The STEM analysis confirmed the heterogeneous distribution of Nd, Fe, Cu, Al, Ni and homogeneous distribution of Ti, Nb and Co. The boundaries of nano grains contain more than 70% ferromagnetic elements, ensuring strong inter-grain coupling among the grains.

  • magnetic properties phase transition temperatures and microstructure of cefeb Alnico ribbons
    Journal of Magnetism and Magnetic Materials, 2019
    Co-Authors: Sajjad Ur Rehman, Han Ouyang, Qingzheng Jiang, Lunke He, Jie Song, Lei Wang, Zhenchen Zhong


    Abstract Alnico 8 elements are added into Ce-Fe-B ribbons and the effects of the multi elements on the magnetic properties, phase transition temperatures and microstructure are investigated. It is found that the addition of Alnico elements is helpful for enhancing the magnetic properties of the Ce-Fe-B alloys. The Curie temperature of Ce2Fe14B (2:14:1) main phase increased from 422 K for the standard alloy to 490 K by 20 wt% addition of Alnico, while the Curie temperature of CeFe2 (1:2) phase decreased from 223 K to 122 K. The transmission electron microscopy (TEM) analysis showed that the nano grains of the alloys are refined which is attributed to the refractory character of Ti. The intergranular exchange interactions measured by applying Henkel plots also enhanced by adding Alnico elements into Ce-Fe-B ribbons. The magnetic properties Hcj, Br and (BH)max improved significantly for the optimized addition of Alnico. Magnetic properties of Hcj = 5.16 kOe, Br = 4.59 kG and (BH)max = 4.14 MGOe are obtained in Ce35Fe56.5(Alnico)7.5B ribbon. The improved magnetic properties in Alnico-doped Ce-Fe-B alloys are attributed to the refined microstructure and enhanced intergranular exchange interactions.

J T Zhao – 2nd expert on this subject based on the ideXlab platform

  • correlations of phase structure and thermal stability for Alnico 8 alloys
    Journal of Magnetism and Magnetic Materials, 2017
    Co-Authors: J T Zhao, X.c. Feng


    Abstract The correlations of phase structure and thermal stability for Alnico 8 alloys is analyzed by three-step aging at 650 °C, 600 °C and 550 °C gradually in this paper. After three-step aging the a1 phase is a chess-like structure in transverse direction and a bamboo-like structure in longitudinal direction. Meanwhile the magnetic energy product ((BH) m ) increases from 9.17 MGOe to 10.59 MGOe, and the remanence temperature coefficient a(RT-180 °C) reduces from −2.31 %%/°C to −1.25 %%/°C. The MPMS and VSM measurements indicate that three-step aging makes the a1 phase be single domain particles and dispersed distribution, which plays an important role in optimizing the thermal stability of Alnico alloys.

  • Effect of Phase Structure on Remanence Thermal Stability of Alnico8 Alloys
    2016 International Conference of Asian Union of Magnetics Societies (ICAUMS), 2016
    Co-Authors: J T Zhao, X.c. Feng


    With the development of technology and application requirements, researchers pay attention to not only magnetic properties of Alnico alloy but also its thermal stability. Their magnetic properties keeps in closely touch with phase microstructure[1], also Liu focuses on the effect of orientation degree of precipitated phase on thermal stability[2]. This paper mainly studies the influence of phase structure to thermal stability of Alnico8 alloys by adjusting the contents of Co and Nb(Sample A:36wt%Co; Sample B:36wt%Co, 1.1wt%Nb; Sample C:35wt%Co, 1.1wt%Nb). The morphology is characterized by Transmission Electron Microscope, the magnetic properties are measured by the B-H apparatus with closed circuit.

  • the phase and microstructure analysis of Alnico magnets with high coercivity
    Journal of Magnetism and Magnetic Materials, 2015
    Co-Authors: J T Zhao


    Abstract Alnico magnets with high coercivity and high magnetic energy (Hc about 2020 Oe, (BH)m about 9.5 MGOe) are obtained by adjusting chemical compositions and optimizing microstructure. The phase and microstructure of Alnico magnets with high (Alnico9h) and low coercivity (Alnico9) are analyzed contrastively. The shape and distribution of FeCo-rich phase (α1) which are needle-like arrangement in Alnico9h are nonuniform, the orientation degree and the volume fraction of α1 phase are less than that of Alnico9. Energy-dispersive X-ray spectroscopy (EDS) research shows that Fe and Co atoms of α1 phase have a homogeneous distribution in Alnico9h magnet in which the boundaries between α1 and AlNi-rich phases (α2) are clearer than those in Alnico9 magnet. Furthermore, the degree for chemical segregation between α1 and α2 phases in Alnico9h is much better than that in Alnico9 magnet.

Iver E. Anderson – 3rd expert on this subject based on the ideXlab platform

  • Processing of Alnico Magnets by Additive Manufacturing
    Applied Sciences, 2019
    Co-Authors: Emma White, Emily A. Rinko, Timothy E. Prost, Timothy Horn, Christopher Ledford, Christopher Rock, Iver E. Anderson


    Permanent magnets without rare earth (RE) elements, such as Alnico, will improve supply stability and potentially decrease permanent magnet cost, especially for traction drive motors and other increased temperature applications. Commercial Alnico magnets with the highest energy product are produced by directional solidification (DS) to achieve a <001> columnar grain orientation followed by significant final machining, adding to the high cost. Additive manufacturing (AM) is an effective method to process near net-shape parts with minimal final machining of complex geometries. AM also, has potential for texture/grain orientation control and compositionally graded structures. This report describes fabrication of Alnico magnets by AM using both laser engineered net shaping (LENS)/directed energy deposition (DED) and electron beam melting powder bed fusion (EBM/PBF). High pressure gas atomized (HPGA) pre-alloyed Alnico powders, with high purity and sphericity, were built into cylindrical and rectangular samples, followed by magnetic annealing (MA) and a full heat treatment (FHT). The magnetic properties of these AM processed specimens were different from their cast and sintered counterparts of the same composition and show a great sensitivity to heat treatment. The AM process parameters used in this developmental study did not yet result in any preferred texture within the Alnico AM builds. These findings demonstrate feasibility for near net-shape processing of Alnico permanent magnets for use in next generation traction drive motors and other applications requiring increased operating temperatures and/or complex engineered part geometries, especially with further AM process development for texture control.

  • texture development and coercivity enhancement in cast Alnico 9 magnets
    AIP Advances, 2018
    Co-Authors: Wenyong Zhang, Ralph Skomski, Iver E. Anderson, J. E. Shield, Shah R Valloppilly, Xingzhong Li, M J Kramer, W Tang, David J. Sellmyer


    The effect of Y addition and magnetic field on texture and magnetic properties of arc-melted Alnico 9 magnets has been investigated. Small additions of Y (1.5 wt.%) develop a (200) texture for the arc-melted Alnico 9 magnet. Such a texture is hard to form in cast samples. To achieve this goal, we set up a high-field annealing system with a maximum operation temperature of 1250 °C. This system enabled annealing in a field of 45 kOe with subsequent draw annealing for the solutionized buttons; we have been able to substantially increase remanence ratio and coercivity, from 0.70 and 1200 Oe for the Y-free Alnico 9 to 0.90 and 1400 Oe for the Y-doped Alnico 9, respectively. A high energy product of 7.3 MGOe has been achieved for the fully heat-treated Y-doped Alnico 9. The enhancement of coercivity is believed to arise from the introduction of magnetocrystalline anisotropy from 80 nm Y2Co17-type grains, which are exchange-coupled to the main-phase Alnico rods.

  • Compression Molding and Novel Sintering Treatments for Alnico Type-8 Permanent Magnets in Near-Final Shape with Preferred Orientation
    JOM, 2017
    Co-Authors: Aaron G. Kassen, Emma M. H. White, Wei Tang, Liangfa Hu, Andriy Palasyuk, Lin Zhou, Iver E. Anderson


    Economic uncertainty in the rare earth (RE) permanent magnet marketplace, as well as in an expanding electric drive vehicle market that favors permanent magnet alternating current synchronous drive motors, motivated renewed research in RE-free permanent magnets like “Alnico,” an Al-Ni-Co-Fe alloy. Thus, high-pressure, gas-atomized isotropic type-8H pre-alloyed Alnico powder was compression molded with a clean burn – out binder to near-final shape and sintered to density >99% of cast Alnico 8 (full density of 7.3 g/cm^3). To produce aligned sintered Alnico magnets for improved energy product and magnetic remanence, uniaxial stress was attempted to promote controlled grain growth, avoiding directional solidification that provides alignment in Alnico 9. Successful development of solid-state powder processing may enable anisotropically aligned Alnico magnets with enhanced energy density to be mass-produced.