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

International Symposium on Ti-based Functional Materials Motivation ◈ Transformation behavior of Ti-Ni alloys Highly sensitive actuator Ti-Ni alloys B2 ↔ B19’B2 ↔ R HysteresisElongationHysteresisElongation >30K~5%2K0.8% ◈ 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

International Symposium on Ti-based Functional Materials - Aging of Ni-rich Ti-Ni alloys : Ti 3 Ni 4 precipitates coherent with matrix S. Miyazaki, K. Otsuka, Matall. Trans. A, 17A (1986) Rapid solidification of Ti-Ni alloys : Ti 2 Ni particles coherent with matrix and high density of dislocations -The third elements (Fe, Cr, Co, Mo) addition to an equiatomic TiNi alloy: induce the R phase without TMT, aging and rapid solidification T.H. Nam,J.H. Kim, M.S. Choi, H.W. Lee. J. Mater. Sci. Lett. 21 (2002)

International Symposium on Ti-based Functional Materials ◈ Electronic configuration of the third element for inducing the R phase in Ti-Ni alloys - Fe: [Ar]3d 6 4s 2 - Cr: [Ar]3d 5 4s - Co: [Ar]3d 7 4s 2 - Mo: [Kr]4d 5 5s Transition metal Transition metal is the prerequisite condition for Inducing the R phase in Ti-Ni alloys ???

International Symposium on Ti-based Functional Materials ◈ Electronic configuration of the third element for inducing the R phase in Ti-Ni alloys - Fe: [Ar]3d 6 4s 2 - Cr: [Ar]3d 5 4s - Co: [Ar]3d 7 4s 2 - Mo: [Kr]4d 5 5s - Sn: [Kr]4d 10 5s 2 5p 2 Transition metal : Not transition metal !!

International Symposium on Ti-based Functional Materials Ti-Ni-Sn alloys prepared by conventional casting Dual phase structure of TiNi and Ti 3 Sn Very fine eutectic structure B. Lu, J. Xu, J. non-cryst. Solids, 354 (2008) 5422 May 15-May 19, 2011 – Hongkong

International Symposium on Ti-based Functional Materials Ti-Ni-Sn alloys prepared by conventional casting Microstructures of Ti-Ni-Sn alloys Ti 3 Sn TiNi(Sn) J.H. Kim, J.P. Noh, Y.M. Im, S. Miyazaki, T.H. Nam; Scripta Mater. Accepted

International Symposium on Ti-based Functional Materials 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

International Symposium on Ti-based Functional Materials Ti-Ni-Sn alloys prepared by conventional casting However, the B2-R is not separated from the R-B19’ Ti-40Ni-5Sn B2-R 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 ? J.H. Kim, J.P. Noh, Y.M. Im, S. Miyazaki, T.H. Nam; Scripta Mater. Accepted

International Symposium on Ti-based Functional Materials -Crystallization and microstructures of rapidly solidified Ti-Ni-Sn alloys -Martensitic transformation behavior of Ti-Ni- Sn alloys Purpose of the present study

International Symposium on Ti-based Functional Materials Experimental method Pre-alloys by arc melting Ti-36Ni-7Sn(at%) Ribbons by melt spinning - Diffrential scanning Calorimetry - X-ray diffraction Transformation behavior -Transmission electron microscopy -Scanning electron microscopy Microstructure Melt-spinning conditions Schematic diagram of melt-spinner parameterCondition Nozzle diameter0.5 mm Ejection pressure0.4 kgf/cm 2 Linear velocity31 m/s Liquid temperature1703 K 3000 rpm Pre-alloy Induction Melting temp. (1703K) Ribbon

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

International Symposium on Ti-based Functional Materials Results & discussion Temperature (K) Heat flow (mW) 20 K/min Crystallization sequence: Amorphous → Ti 2 Ni → B2 → Ti 3 Sn Heating samples at various temperatures in DSC P AS P: Amorphous → Ti 2 Ni A: Amorphous → B2 S: Ti 2 Ni → Ti 3 Sn + B2

International Symposium on Ti-based Functional Materials Results & discussion IngotRibbon 5 um Ti 3 Sn at.% Ti73.9 Sn26.1 at.% Ti50.8 Ni48.6 Sn0.6 Matrix includes small amount of Sn Very fine eutectic structure in ribbon Ti-Ni-Sn 1263 K

International Symposium on Ti-based Functional Materials Results & discussion 873K Ti 2 Ni Ti 3 Sn TiNi(B2) Increase in the average size and amount of Ti 3 Sn with raising annealing temperature 1273 K

International Symposium on Ti-based Functional Materials Results & discussion x120K 50nm Annealed at 773 K Spherical Ti 2 Ni particles embedded in amorphous (000) (111) (200) (1-1-1) [01-1]Ti 2 Ni

International Symposium on Ti-based Functional Materials Results & discussion x60K 100nm Annealed at 873 K Ti 2 Ni and B2 particles coexist Crystallization is finished

International Symposium on Ti-based Functional Materials 50 nm Annealed at 1073 K Specific orientation relationship between B2-Ti 2 Ni B2-Ti 3 Sn

International Symposium on Ti-based Functional Materials 773K 873K 973K 1073K Results & discussion Particle size of Ti 2 Ni, Ti 3 Sn and B2 parent phase increases with raising annealing temperature

International Symposium on Ti-based Functional Materials Results & discussion 7Sn K K 6.9 J/g 4.1 J/g 12.7 J/g K K 3.7 J/g 3.6 J/g K K 2.6 J/g 2.7 J/g K K 3.9 J/g 5.1 J/g K 281.9˚C 3.0 J/g 4.4 J/g Temperature (K) Heat flow (J/g) Temperature (K) 7Sn ` Ti 2 Ni Ti 3 Sn TiNi(B2) K

International Symposium on Ti-based Functional Materials Results & discussion B19’(002) R(011) R(101) B19’(012) R(011) B19’(111) Annealed at 1073 K B2→R →B19’ martensitic transformation B2→R R→B19’ K K 3.9 J/g 5.1 J/g K 281.9˚C 3.0 J/g 4.4 J/g B2-R R-B19’

International Symposium on Ti-based Functional Materials Results & discussion K K K K K Heat flow (J/g) Rapid solidification 4.08 J/g 6.39 J/g 5.04 J/g 3.88 J/g TR*TR* K MS*MS* K K 13.8 J/g 12.7 J/g Conventional casting Temperature (K) B2→R →B19’ TR*TR* MS*MS* ΔT(T R * - M S *) = 24 KΔT(T R * - M S *) = 102 K Rapid solidification is effective to separate the B2-R from the R-B19’

International Symposium on Ti-based Functional Materials Conclusions 1) Rapidly solidified Ti-36Ni-7Sn(at%) alloy ribbon was amorphous and activation energy for crystallization was determined to be ± 9.0 kJ/mol 2) The ribbon was crystallized in the sequence of amorphous - Ti 2 Ni - B2- Ti 3 Sn 3) Rapid solidification of Ti-36Ni-7Sn alloy followed by crystallization induced nanostructured ribbon which consisted of the B2, Ti 2 Ni and Ti 3 Sn. 4) Ti 2 Ni(P) and Ti 3 Sn(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 T R *and M S *in the ribbon was larger than that of the ingot prepared by conventional casting.

International Symposium on Ti-based Functional Materials May 15-May 19, 2011 – Hongkong Thank you for your attention!