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Crystallization Behavior and Microstructure of Ti-Ni-Sn Alloys

This study investigates the crystallization behavior and microstructure of Ti-Ni-Sn alloys prepared by conventional casting. The rapid solidification process separates the B2-R and R-B19' martensitic transformations, and the addition of Sn enhances the formation of Ti3Sn phase. Results show that the size and amount of Ti3Sn particles increase with higher annealing temperature.

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Crystallization Behavior and Microstructure of Ti-Ni-Sn Alloys

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  1. Crystallization Behavior and Microstructure of Ti-Ni-Sn Alloys * Tae-hyun Nam, Hui-jin Choi, Min-soo Kim, Jae-hyun Kim ** Yeon-wook Kim * School of Materials Science and Engineering, Gyeongsang National University, Korea ** Department of Materials Science and Engineering, Kemyung University, Korea

  2. Motivation • Transformation behavior of Ti-Ni alloys Highly sensitive actuator • Methods for inducing the R phase • Thermo-mechanical treatments of an equiatomic Ti-Ni alloy : Introduction of dislocations S. Miyazaki, K. Otsuka, Matall. Trans. A, 17A (1986) 53-63

  3. Aging of Ni-rich Ti-Ni alloys : Ti3Ni4 precipitates coherent with matrix S. Miyazaki, K. Otsuka, Matall. Trans. A, 17A (1986) 53-63 • Rapid solidification of Ti-Ni alloys : Ti2Ni particles coherent with matrix and high density of dislocations T.H. Nam,J.H. Kim, M.S. Choi, H.W. Lee. J. Mater. Sci. Lett. 21 (2002) 799-801 • The third elements (Fe, Cr, Co, Mo) addition to an equiatomic TiNi alloy: induce the R phase without TMT, aging and rapid solidification

  4. Electronic configuration of the third element for inducing the R phase in Ti-Ni alloys • Fe: [Ar]3d64s2 • Cr: [Ar]3d54s • Co: [Ar]3d74s2 • Mo: [Kr]4d55s Transition metal Transition metal is the prerequisite condition for Inducing the R phase in Ti-Ni alloys ???

  5. Electronic configuration of the third element for inducing the R phase in Ti-Ni alloys • Fe: [Ar]3d64s2 • Cr: [Ar]3d54s • Co: [Ar]3d74s2 • Mo: [Kr]4d55s • Sn: [Kr]4d105s25p2 Transition metal : Not transition metal !!

  6. May 15-May 19, 2011 – Hongkong Ti-Ni-Sn alloys prepared by conventional casting • Dual phase structure of TiNi and Ti3Sn • Very fine eutectic structure B. Lu, J. Xu, J. non-cryst. Solids, 354 (2008) 5422

  7. Ti-Ni-Sn alloys prepared by conventional casting Microstructures of Ti-Ni-Sn alloys TiNi(Sn) J.H. Kim, J.P. Noh, Y.M. Im, S. Miyazaki, T.H. Nam; Scripta Mater. Accepted Ti3Sn

  8. Ti-Ni-Sn alloys prepared by conventional casting The B2-R-B19’ two-stage martensitic transformation : J.H. Kim, J.P. Noh, Y.M. Im, S. Miyazaki, T.H. Nam; Scripta Mater. Accepted

  9. Ti-Ni-Sn alloys prepared by conventional casting However, the B2-R is not separated from the R-B19’ Rapid solidification has been known to separate the B2-R from the R-B19’ in Ti-Ni alloys Rapid solidification is expected to separate the B2-R from the R-B19’ in Ti-Ni-Sn alloys ? R-B19’ B2-R Ti-40Ni-5Sn J.H. Kim, J.P. Noh, Y.M. Im, S. Miyazaki, T.H. Nam; Scripta Mater. Accepted

  10. Purpose of the present study • Crystallization and microstructures of rapidly solidified Ti-Ni-Sn alloys • Martensitic transformation behavior of Ti-Ni-Sn alloys

  11. Experimental method Pre-alloy InductionMelting temp.(1703K) Ribbon 3000 rpm Transformation behavior Microstructure - Diffrential scanning Calorimetry - X-ray diffraction • Transmission electron microscopy • Scanning electron microscopy Pre-alloys by arc melting Ti-36Ni-7Sn(at%) Ribbons by melt spinning Schematic diagram of melt-spinner Melt-spinning conditions

  12. Results & discussion Amorphous Heating 25 K / min Heat flow (mW) 20 K / min • Temperature (˚C) 15 K / min 10 K / min 5 K / min • Heating rate (˚C/min) Temperature (K) • Temperature (˚C) Activation energy for crystallization: 165.1 ± 9.0 kJ/mol which is very small comparing with Ti-Ni and Ti-Ni-Cu alloys (>~300 kJ/mol) Ea = 165.1 ± 9.0 KJ/mol

  13. Results & discussion Heating samples at various temperatures in DSC 20 K/min P Crystallization sequence: Amorphous → Ti2Ni → B2 → Ti3Sn Heat flow (mW) A S Temperature (K) P: Amorphous → Ti2Ni A: Amorphous → B2 S: Ti2Ni → Ti3Sn + B2

  14. Results & discussion Ingot Ribbon 1263 K Ti-Ni-Sn Ti3Sn 5 um • Matrix includes small amount of Sn • Very fine eutectic structure in ribbon

  15. 873K Results & discussion TiNi(B2) Ti3Sn Ti2Ni 1273 K Increase in the average size and amount of Ti3Sn with raising annealing temperature

  16. Results & discussion Annealed at 773 K Spherical Ti2Ni particles embedded in amorphous x120K 50nm (200) (1-1-1) (111) (000) [01-1]Ti2Ni

  17. Results & discussion • x60K • 100nm Annealed at 873 K Ti2Ni and B2 particles coexist Crystallization is finished

  18. (211)B2 (200)B2 (222)Ti2Ni (002)Ti2Ni (220) Ti2Ni (011)B2 (000) (200)B2 // (008)Ti2Ni (011)B2 // (440)Ti2Ni [01-1]B2 // [1-10]Ti2Ni (110)B2 (200)B2 (101)Ti3Sn (100)Ti3Sn (000) (001) Ti3Sn (1-10)B2 [001]B2 // [010]Ti3Sn Annealed at 1073 K Specific orientation relationship between B2-Ti2Ni B2-Ti3Sn 50 nm 50 nm

  19. Results & discussion 773K Particle size of Ti2Ni, Ti3Sn and B2 parent phase increases with raising annealing temperature 873K 973K 1073K

  20. TiNi(B2) Ti3Sn Ti2Ni Results & discussion 7Sn 7Sn 291.9 K 237.8 K 291.9 K ` 4.1 J/g 6.9 J/g 3.7J/g 12.7 J/g 3.6 J/g 296.6 K 297.4 K Temperature (K) 299.1 K 303.2 K 187.4 K 3.9 J/g Heat flow (J/g) 2.6 J/g 4.4 J/g 2.7 J/g 3.0 J/g 5.1 J/g 281.9˚C 307.6 K 303.8 K Temperature (K)

  21. R(101) R(101) Results & discussion Annealed at 1073 K R(011) R(011) B19’(111) B19’(012) B19’(002) B2→R B2-R R-B19’ 299.1 K R→B19’ 187.4 K 3.9 J/g 4.4 J/g 3.0 J/g 5.1 J/g 281.9˚C 303.8 K B2→R →B19’ martensitic transformation

  22. Conventional casting Rapid solidification TR* MS* 311.0K 301.5K 12.7 J/g 5.04 J/g 3.88 J/g Heat flow (J/g) 13.8 J/g 4.08 J/g 6.39 J/g 327.4 K 306.2 K 285.1 K 319.4 K 290.2 K 304.3 K Temperature (K) Results & discussion B2→R →B19’ B2→R →B19’ TR* MS* ΔT(TR* - MS*) = 24 K ΔT(TR* - MS*) = 102 K Rapid solidification is effective to separate the B2-R from the R-B19’

  23. Conclusions 1) Rapidly solidified Ti-36Ni-7Sn(at%) alloy ribbon was amorphous and activation energy for crystallization was determined to be 165.1 ± 9.0 kJ/mol 2) The ribbon was crystallized in the sequence of amorphous - Ti2Ni - B2- Ti3Sn 3) Rapid solidification of Ti-36Ni-7Sn alloy followed by crystallization induced nanostructured ribbon which consisted of the B2, Ti2Ni and Ti3Sn. 4) Ti2Ni(P) and Ti3Sn(S) had specific orientation relationships with the B2 phase(B), (011)B//(220)P, [01-1]B//[1-10]P and (110)B//(100)S, [001]B//[010]S, respectively. 5) The crystallized ribbon showed the B2-R-B19’ martensitic transformation behavior. 6) The temperature gap between TR*and MS*in the ribbon was larger than that of the ingot prepared by conventional casting.

  24. May 15-May 19, 2011 – Hongkong Thank you for your attention!

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