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Workshop on Atomic-Scale Challenges in Advanced Materials: Defects in Materials Turku, Finland

Composition dependent properties of Ni 2 MnGa based ferromagnetic shape memory alloys Qing-Miao Hu Institute of Metal Research, Chinese Academy of Sciences Wenhua Road 72, Shenyang 110016, China. Workshop on Atomic-Scale Challenges in Advanced Materials: Defects in Materials Turku, Finland

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Workshop on Atomic-Scale Challenges in Advanced Materials: Defects in Materials Turku, Finland

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  1. Composition dependent properties of Ni2MnGa based ferromagnetic shape memory alloysQing-Miao HuInstitute of Metal Research, Chinese Academy of SciencesWenhua Road 72, Shenyang 110016, China Workshop on Atomic-Scale Challenges in Advanced Materials: Defects in Materials Turku, Finland August 22-23, 2013

  2. Co-workers • Dr. Hu-Bin Luo • Institute of Metal Research, Chinese Academy of Sciences • Dr. Chun-Mei Li • Institute of Metal Research, Chinese Academy of Sciences • Royal Institute of Technology/Uppsala University , Sweden • Prof. Rui Yang • Institute of Metal Research, Chinese Academy of Sciences • Prof. Börje Johansson • Royal Institute of Technology/Uppsala University , Sweden • Prof. LeventeVitos • Royal Institute of Technology/Uppsala University , Sweden

  3. Outline • Background and Motivation • Method • Results and Discussion • Site-occupancy • Elastic modulus • Phase stability • Summary

  4. Outline • Background and Motivation • Method • Results and Discussion • Site-occupancy • Elastic modulus • Phase stability • Summary

  5. Background and MotivationGeneral Ni2MnGa: Heusler Alloys Structure Transition: Cubic L21Austinite Orthorhombic Martensite Reversible: Shape Memory Effect c/a >1 c/a = 1 Mn: 3.86, Ni: <0.3, Ga: 0.00 Magnetic Transition: Ferromagnetic  Paramagnetic c/a <1

  6. Background and MotivationGeneral Perfect Ni2MnGa 202 K 376 K • Coupling between the structure and magnetic transitions leads to some unique properties: • Giant magnetocaloric effect; • Magnetostriction; • Magnetoresistance. • Potential applications: • Magnetic refrigeration; • Magnetostrictive transducers; • etc.

  7. Background and MotivationGeneral Fe doped Ni2MnGa Khovaylo, et al., Phys. Rev. B 72, 224408 (2005) Tsuchiya, et al., ISIJ International 46, 1283 (2006) How to control composition to achieve desirable TM? Can we find some easy predictors to connect composition and TM?

  8. Background and MotivationPredictors for the composition dependence of TM 1. Number of valence electrons per atom (e/a) and TM Chernenko, et al., Acat Mater. 50, 53 (2002)

  9. Background and MotivationPredictors for the composition dependence of TM 2. c/a ratio of martensite and TM Lanska, et al., J. Appl. Phys 95, 8074 (2004)

  10. Background and MotivationPredictors for the composition dependence of TM 3. Energy difference between austinite and martensite (E) and TM Chen, et al., Appl. Phys. Lett. 89, 231921 (2006)

  11. Background and MotivationPredictors for the composition dependence of TM 4. Elastic modulus Cand TM? NiTi SMA：Larger C of the austenite corresponding to lower TM. Ren and Otsuka, Mater Sci Forum (2000) Bungaro and Rabe, Phys. Rev. B, 2003

  12. Background and MotivationPhase stability: Structure of modulated martensite a a The modulated structure is very complex: shear: changing c/a; shuffle: wave-like movement of atoms on [110] Alloying effect on the modulated structure?

  13. Outline • Background and Motivation • Method • Results and Discussion • Site-occupancy • Elastic modulus • Phase stability • Summary

  14. MethodEMTO-CPA First-principles method based on density functional theory Basis Sets: Exact muffin-tin orbitials (EMTO), spdf Exchange-correlation functional: GGA-PBE Coherent potential approximation for the random distribution of alloying atoms.

  15. Outline • Background and Motivation • Method • Results and Discussion • Site-occupancy • Elastic modulus • Phase stability • Summary

  16. GaNi Ga Ni Direct site-occupancy Mn MnNi GaMn Indirect site-occupancy Results and DiscussionSite-occupancy in Ni2MnGa based alloys Ni2-xMnGa1+x Ni2MnGa Geometry of Ni2MnGa projected to (001) plane

  17. Results and DiscussionSite-occupancy in Ni2MnGa based alloys Free energy of different site-occupancy configurations Off-stoichiometric: Indrect: Ga-rich Ni-deficient alloys, forming GaMn and MnNi. Fe/Co/Cu doped: Indirect: Fe-doped Ga-deficient alloys Co-doped Mn- or Ga-deficient alloys Cu always take direct site-occupancy Phys. Rev. B 79, 144112 (2009); 84, 024206 (2011)

  18. Outline • Background and Motivation • Method • Results and Discussion • Site-occupancy • Elastic modulus • Phase stability • Summary

  19. Results and DiscussionElastic modulus and TM Off-stoichiometric Ni2MnGa Fe/Co/Cu doped Ni2MnGa Phys. Rev. B 79, 144112 (2009) Phys. Rev. B 84, 024206 (2011)

  20. Results and DiscussionElastic modulus and TM Ni2Mn(Ga1-xAlx) Acta Mater. 59, 5938(2011)

  21. Outline • Background and Motivation • Method • Results and Discussion • Site-occupancy • Elastic modulus • Phase stability • Summary

  22. Results and DiscussionPhase stability of Ni2Mn(Ga1-xAlx) a a 5L modulated martensite: Martynov et al.. J. Phys. III 2, 739(1992) Two degrees of freedom optimization: Shear: c/a; Shuffle:  Acta Mater. 59, 5938(2011)

  23. Results and DiscussionPhase stability of Ni2Mn(Ga1-xAlx) EAM=EA-EM Martensite more stable

  24. Results and DiscussionPhase stability of Ni2(Mn1-xFex)Ga

  25. Results and DiscussionPhase stability of Ni2(Mn1-xFex)Ga EAM=EA-EM L21 austinite becomes elastically softer with increasing Fe: Lattice vibration contribute more to the free nergy accordingly, stabilizing L21

  26. Outline • Background and Motivation • Method • Results and Discussion • Site-occupancy • Elastic modulus • Phase stability • Summary

  27. Summary • We predict that indrect site-occupation occurs in some of the off-stoichiometric and Fe/Co/Cu doped Ni2MnGa alloys. • The general TM~C′ correlation works for some of the alloys for which the TM~e/a correlation fails. However, there are several cases where both the general TM~C′ and TM~e/a correlations break down. • We present a feasible approach to study the 5-layer modulated (5M) martensitic structure of Ni2MnGa-based alloy using first-principles methods. By using this approach, the 5M martensitic structure of Ni2MnGa is reasonably reproduced and the Al/Fe-doping effects are predicted.

  28. Thank you for your attention!

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