COERCIVITY STUDY OF THERMALLY PROCESSED Nd-Fe-B-TYPE HDDR-TREATED MATERIAL
- Alternative Title
- 열적으로 가공한 Nd-Fe-B계 HDDR 처리 재료의 보자력에 관한 연구
- Abstract
- This project focused on the coercivity behavior of thermally processed Nd12.5Fe80.6B6.4Ga0.3Nb0.2 HDDR-treated material. The research was carried out emphasizing on the following three categories: the residual hydrogen in the Nd-Fe-B-type HDDR-treated material, the effect of residual hydrogen on the coercivity of heated HDDR-treated material, and the coercivity of hot-pressed compacts of HDDR-treated material. The HDDR-treated material contained significant amount of residual hydrogen (1500 ppm). The presence of hydrogen in the HDDR-treated material was examined by hydrogen analysis and desorption behavior on heating. The effect of residual hydrogen on coercivity of the heated Nd-Fe-B-type HDDR-treated material was investigated. The material was heated in Ar atmosphere or in vacuum with distinctively different evacuation speed. The coercivity of the HDDR-treated material was radically reduced around 650 °C or above when the material was heated in Ar or in vacuum with slow pumping speed. The coercivity reduction was much more profound for the material heated in Ar atmosphere or in vacuum with slow pumping speed than in vacuum with high pumping speed heating chamber. This fact can be explained that the residual hydrogen was desorbed more effectively in the course of heating in vacuum with high pumping speed than in Ar or vacuum with slow pumping speed. The coercivity reduction in the HDDR-treated material on heating is believed to be attributed to the disproportionation of Nd2Fe14BHx hydride formed by the residual hydrogen in it. The residual hydrogen is considered as a technical barrier for the thermal process of HDDR-treated material without losing magnetic performance. It was witnessed that coercivity loss in the HDDR material was inconsiderable despite heating at elevated temperature if the residual hydrogen could be desorbed effectively on heating. The HDDR-treated material was compacted by hot-pressing in the closed and open-type die in terms of different evacuation system. The coercivity loss in the compact prepared in the closed-type die above 650 °C was more radical than in the compact prepared in the open die. Residual hydrogen in the HDDR-treated material was desorbed more effectively in the open die compared to the closed-type die on heating for hot-pressing. The coercivity retaining rate was 80 % (10.8 out of 13.5 kOe) in the full dense compact prepared in the open die. The rate was only 28 % (3.8 out of 13.5 kOe) in the full dense compact prepared in the closed die. The present findings suggest that the coercivity of the HDDR-treated material is affected radically by the residual hydrogen if it is not desorbed effectively on thermal processing.
- Issued Date
- 2014
- Awarded Date
- 2014. 2
- Type
- Dissertation
- Publisher
- Pukyong National University
- Alternative Author(s)
- MD압들머틴
- Affiliation
- Graduate School of Engineering
- Department
- 대학원 재료공학과
- Advisor
- Hae-Woong Kwon
- Table Of Contents
- CHAPTER ONE GENERAL INTRODUCTION PAGE No.
1.1 Development of Nd-Fe-B-type Permanent Magnet…..................... 1
1.2 Applications and Prospects of Permanent Magnet.................……. 3
1.3 Processing Routes of Nd-Fe-B-type Permanent Magnet................. 5
1.4 Excellence of HDDR Process …………..……...............…………. 8
1.5 Objectives of this Thesis…………...…................…………….…… 9
1.6 Scopes of the Thesis.……….......................………………............. 11
1.7 References………................…………………………………........ 12
CHAPTER TWO MAGNETISM AND MAGNETIC
MATERIALS
2.1 Magnetism........................……………………………………….... 15
2.2 Classification of Magnetism and Magnetic Materials .................... 15
2.2.1 Diamagnetism………………................………………….. 16
2.2.2 Paramagnetism…................……….…………………….... 17
2.2.3 Ferromagnetism…................……………………………... 18
2.2.4 Antiferromagnetism…..................……………………….. 19
2.2.5 Ferrimagnetism….................…………………………….. 20
2.3 Electronic Configuration of Rare Earth-Transition Metal Compounds
2.3.1 In the Rare-Earth (R) Series…..............................………... 21
2.3.2 In the Transition-Metal (T) Elements: Fe, Co and Ni.......... 22
2.3.3 Rare Earth-Transition Metal Compounds............................. 23
2.4 Some Properties of Ferromagnetic Materials
2.4.1 Curie Temperature: Tc.................…..………………….... 24
2.4.2 Magnetic Anisotropy................…………...……………. 25
2.4.3 Magnetic Domain…...............………………………...... 26
2.4.4 Domain Wall Process.................………………………… 28
2.4.5 Origin of Coercivity….………................…..................... 29
2.4.6 Hysteresis Loop and Magnetization Process….................. 32
2.4.7 Maximum Energy Product .......…...…............................. 35
2.5 Units of Magnetism…..............….....……………..…..........….... 36
2.6 References……...……...................….……………………............ 37
CHAPTER THREE APPARATUS AND
EXPERIMENTAL PROCEDURE
3.1 Experimental Procedure…..................….…………….……….... 38
3.2 HDDR Process….................…………….…………………….... 39
3.3 Consolidation of HDDR-treated Material.…....................…….... 41
3.4 Heat Treatment of HDDR-treated Material….....................…….. 44
3.5 Magnetic Characterization……..................…….……………….. 46
3.6 Microstructure Analysis
3.6.1 Scanning Electron Microscopy (SEM)…..................…….. 49
3.6.2 Transmission Electron Microscopy (TEM) .................…... 50
3.6.3 X-ray Diffraction (XRD)…………..................……………. 53
3.6.4 Crystal Lattice Parameters by XRD…….................……….. 56
3.7 Differential Thermal Analysis (DTA)….................…................. 57
3.8 Thermopiezic Analyser (TPA)……................……………............. 59
3.9 References……..................………………………………............. 61
CHAPTER FOUR A STUDY OF RESIDUAL
HYDROGEN IN Nd-Fe-B-TYPE
HDDR-TREATED MATERIAL
Abstract……..................…………….…………………………... 62
4.1 Introduction...................………………………………………...... 63
4.2 Experimental Work……….................………………………...... 64
4.3 Results and Discussion…..................…………………………...... 65
4.4 Conclusion……………………..................…………………….... 71
4.5 References…………......................……………………………..... 71
CHAPTER FIVE EFFECT OF RESIDUAL
HYDROGEN ON COERCIVITY OF
HEATED Nd-Fe-B-TYPE HDDR-
TREATED MATERIAL
Abstract…………..…..................…………………………….….. 73
5.1 Introduction………….…..................…………………………...... 74
5.2 Experimental Work…...................……………………………...... 75
5.3 Results and Discussion..................……………………………..... 75
5.4 Conclusion……......................………………………………….... 85
5.5 References…..................………………………..…………….….. 86
CHAPTER SIX COERCIVITY OF HOT-PRESSED
COMPACTS OF Nd-Fe-B-TYPE
HDDR-TREATED MATERIAL
Abstract ………..…..................……...…………………………... 88
6.1 Introduction………...................………………………………….. 89
6.2 Experimental Work……..................….………………………….. 90
6.3 Results and Discussion..................…….………………………… 91
6.4 Conclusion………......................………………………………… 102
6.5 References................………….………………………………….. 103
CHAPTER SEVEN
SUMMERY…...................…………………………………………….. 105
APPENDIX: Publications……....................…………………………... 109
- Degree
- Doctor
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