Mechanism of magnetic field-induced strain

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Table of contents

Chapter 1 Literature Review
1.1 General introduction
1.2 Martensitic transformation and twin relationship between variants
1.3 Ni-Mn-Ga Ferromagnetic Shape Memory Alloys
1.3.1 Introduction
1.3.2 Magneto-structural transformation in Ni-Mn-Ga alloys
1.3.3 Crystal structure of martensite
1.3.4 Ferromagnetism of Ni-Mn-Ga alloys
1.3.5 Mechanism of magnetic field-induced strain
1.3.6 Crystallographic orientation relationship of Ni-Mn-Ga alloys
1.4 Content of the present work
Chapter 2 Experimental and calculation methods
2.1 Alloy preparation
2.2 Sample preparation
2.3 Characterization methods
2.3.1 Optical microscopy
2.3.2 Mechanical property testing
2.3.3 Differential scanning calorimetry
2.3.4 X-ray diffraction
2.3.5 Scanning electron microscopy
2.3.6 Transmission electron microscopy
2.4 Crystallographic calculation method
2.4.1 Coordinate transformation between orthonormal reference system and monoclinic system 30􀀃
2.4.2 Misorientation calculation
Chapter 3 Characterization of Ni-Mn-Ga martensites
3.1 5M martensite
3.1.1 Crystal structure of 5M martensite
3.1.2 Microstructural features of 5M martensite
3.1.3 Orientation identification of 5M martensite
3.1.4 Orientation relationships between martensite variants
3.1.5 Characters of twin interface planes
3.1.6 Orientation relationship between austenite and 5M martensite
3.1.7 Summary
3.2 7M Martensite
3.2.1 Phase transformation temperatures and mechanical property
3.2.2 Crystal structure of 7M martensite
3.2.3 Microstructure
3.2.4 Determination of twin relationships and twin interfaces of 7M martensite
3.2.5 Orientation relationship between austenite and 7M martensite
3.2.6 Summary
3.3 Non-modulated martensite
3.3.1 Phase transformation temperatures and crystal structure
3.3.2 Compressive properties
3.3.3 Microstructure
3.3.4 Determination of inter-plate and inter-lamellar interface
3.3.5 Summary
Chapter 4 Austenite-7M-NM transformation
4.1 Formation of self-accommodated 7M martensite
4.1.1 Martensitic transformation temperatures and crystal structure
4.1.2 Microstructure features of austenite to 7M transformation
4.1.3 Confirmation of the orientation relationship between austenite and 7M martensite
4.1.4 Experimental determination of habit plane
4.1.5 Calculation based on the crystallographic phenomenological theory
4.1.6 Summary
4.2 Clarification of structure and stability of long-period modulated martensite
4.2.1 Lattice modulation and nanotwin combination
4.2.2 EBSD measurements on the coexistence of three phases
4.2.3 Inter-plate interface
4.2.4 Summary
4.3 Role of 7M martensite in the transformation from austenite to NM martensite
4.3.1 EBSD measurements on the co-existing austenite, 7M martensite and NM martensite
4.3.2 Orientation relationship between 7M martensite and NM martensite
4.3.3 Transformation mechanism from 7M martensite to NM martensite
4.3.4 Summary
Chapter 5 Conclusion and perspective
Conclusion
Perspective
Appendix I: atomic coordinates of 5M superstructure
Appendix II: atomic coordinates of incommensurate 7M superstructure
Appendix III: atomic coordinates of nanotwinned 7M superstructure
References