Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Reports 2016 INVESTIGATION OF THE RESISTANCE TO DEMAGNETIZATION IN BULK RARE-EARTH MAGNETS COMPRISED OF CRYSTALLOGRAPHICALLY-ALIGNED, SINGLE-DOMAIN CRYSTALLITES WITH MODIFIED INTERGRANULAR PHASE Jie Li Michigan Technological University, [email protected] Copyright 2016 Jie Li Recommended Citation Li, Jie, "INVESTIGATION OF THE RESISTANCE TO DEMAGNETIZATION IN BULK RARE-EARTH MAGNETS COMPRISED OF CRYSTALLOGRAPHICALLY-ALIGNED, SINGLE-DOMAIN CRYSTALLITES WITH MODIFIED INTERGRANULAR PHASE", Open Access Dissertation, Michigan Technological University, 2016. https://doi.org/10.37099/mtu.dc.etdr/131 Follow this and additional works at: https://digitalcommons.mtu.edu/etdr Part of the Engineering Physics Commons, and the Metallurgy Commons INVESTIGATION OF THE RESISTANCE TO DEMAGNETIZATION IN BULK RARE-EARTH MAGNETS COMPRISED OF CRYSTALLOGRAPHICALLY- ALIGNED, SINGLE-DOMAIN CRYSTALLITES WITH MODIFIED INTERGRANULAR PHASE By Jie Li A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY In Engineering Physics MICHIGAN TECHNOLOGICAL UNIVERSITY 2016 © 2016 Jie Li This dissertation has been approved in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY in Engineering Physics. Department of Physics Dissertation Advisor: Peter D. Moran Committee Member: Ravindra Pandey Committee Member: Stephen Hackney Committee Member: Stephen Kampe Committee Member: Yongmei Jin Department Chair: Ravindra Pandey Content List of Tables ..................................................................................................................... vi List of Figures ................................................................................................................... vii Acknowledgements ............................................................................................................ xi Abstract ............................................................................................................................ xiii Chapter 1 Introduction ................................................................................................... 1 1.1 Research Goal ...................................................................................................... 1 1.2 Motivations for Research ..................................................................................... 2 1.3 Organization of the Dissertation .......................................................................... 3 Chapter 2 Background ................................................................................................... 5 2.1 Intrinsic Magnetic Properties ............................................................................... 5 2.2 Effect of Chemical Compositions on MS and HK ................................................. 8 2.3 Effect of Volume Percent of Hard Phase on MS and HK .................................... 11 2.4 Demagnetization Curves and the Definition of Coercivity and Remanence ..... 11 2.5 Effect of Microstructure on HC and Br ............................................................... 13 2.5.1 Magnetic Domain........................................................................................ 14 2.5.2 The Phenomenological Model for Understanding the Impact of Microstructure on Hc ................................................................................................ 16 iii 2.6 Methods of Manufacturing RE2TM14B Magnets ............................................... 19 2.6.1 Sintering Process ......................................................................................... 19 2.6.2 Hot-Deformation Process............................................................................ 22 2.6.3 Preferential Dissolution/Re-precipitation Mechanism ................................ 24 2.7 The Effect of Intergranular Phase on Magnetic Properties ................................ 27 Chapter 3 Experimental Techniques............................................................................ 31 3.1 Grain Size Measurement .................................................................................... 31 3.2 Developing a Quantitative Metric of Crystallographic Alignment .................... 32 3.3 Measuring Remanence and Coercivity with VSM ............................................. 37 Chapter 4 Characteristics of RE2TM14B Magnets Used in Traction Motors of Hybrid and Electric Vehicles ............................................................................................................... 39 4.1 Structure of the Experiments ................................................................................ 40 4.2 Results and Discussion ......................................................................................... 41 4.3 Conclusions ........................................................................................................... 47 Chapter 5 Impact of Hot-deformation Parameters on Microstructural and Magnetic Properties of RE2TM14B Magnets .................................................................................... 49 5.1 Experimental Design ............................................................................................. 50 5.2 Results and Discussion ......................................................................................... 51 5.2.1 Hot Deformation Parameters on Microstructural Properties of Magnets ...... 52 5.2.2 Hot Deformation Parameters on Magnetic Properties of Magnets ................ 59 iv 5.3 Conclusions ........................................................................................................... 61 Chapter 6 Effect of Modifying Inter-granular Phase on Microstructural and Magnetic Properties of RE2TM14B Magnets .................................................................................... 62 6.1 Experimental Design ............................................................................................. 63 6.2 Results and Discussion ......................................................................................... 64 6.2.1 Microstructural Properties of Hot-deformed Magnets with Modified Intergranular Phase ................................................................................................... 64 6.2.2 Magnetic Properties of Developed Hot-deformed Magnets ............................ 68 6.2.3 Impact of Diluting Intergranular Phase on Magnetic Properties of Hot-deformed Magnets ..................................................................................................................... 71 6.3 Conclusions ........................................................................................................... 81 Chapter 7 Summary .......................................................................................................... 83 References ......................................................................................................................... 86 v List of Tables Table 2-1 Other research work on analyzing the impact of intergranular phase on magnetic properties of Nd2Fe14B-based materials ............................................................................ 27 Table 4-1The chemical compositions of the materials examined in this work ................. 41 Table 5-1Hot deformation parameters for each sample .................................................... 51 Table 6-1 Calculated value of MS, HK for [Dy0.08Pr0.24Nd0.68]2[Fe0.94Co0.06]14B and experimental value of MS, HK for Nd2Fe14B ..................................................................... 74 Table 6-2 Values of parameters α and Neff for hot-deformed Nd2Fe14B-based magnetic materials. ........................................................................................................................... 75 vi List of Figures Figure 2-1 The tetragonal unit cell of the Nd2Fe14B crystal structure, image created with Pearson’s Crystal Data software using a crystallography data base[1]. ............................. 8 Figure 2-2 Saturation magnetization and anisotropy field of pure RE2Fe14B magnet as a function of temperature.[5] ............................................................................................... 10 Figure 2-3 Saturation magnetization and anisotropy field of Nd2[Fe1-mCom]14B at different temperatures.[6] ................................................................................................................ 10 Figure 2-4 A typical hysteresis loop of a permanent magnet. .......................................... 13 Figure 2-5 The formation of magnetic domains. .............................................................. 14 Figure 2-6 Sketch of magnetic press part in the magnetic sintering process .................... 20 Figure 2-7 Cross-sectional SEM image of sintered magnets. ........................................... 21 Figure 2-8 Surface Dy diffusion process patterned by Hitachi. ........................................ 21 Figure 2-9 General steps of hot-deformation process: (1) melt-spining, (2) hot pressing and (3) hot deformation ........................................................................................................... 23 Figure 2-10 Microstructures of (a) sintered magnets and (b) hot-deformed magnets measured by SEM. ............................................................................................................ 24 Figure 2-11 Under