### Abstract

A clear relationship between the hysteresis of shape memory alloys and the middle eigenvalue of their transformation stretch tensor (λ_{2}) has recently been demonstrated experimentally and theoretically. As λ_{2} gets closer to 1, the geometric: compatibility between austenite and martensite increases as predicted in the geometric nonlinear theory of martensite (GNLTM)[1] and leads to a drop in hysteresis. Changes in microstructure are investigated by conventional transmission electron microscopy and electron diffraction for the Ti_{50}Ni_{50-x}Pd_{x} system over a range of compositions around the compatibility condition. Alloys sitting far enough above λ_{2} = 1, i.e. x>20, show a common microstructure for SMAs, consisting of parallel bands of martensite twinned along the {111} type I lattice invariant shear (LIS). This microstructure changes gradually as we tune the composition to approach the compatibility condition. The twinning ratio of martensite plates decreases until the plates become a single variant. The banded morphology is replaced by an apparent random mosaic of twinless martensite plates where self-accommodation seems to play an important role. In addition the in-situ growth of martensite in the austenite near the compatibility condition was observed and showed exact austenite-martensite interfaces along the predicted habit planes.

Original language | English (US) |
---|---|

Title of host publication | Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08 |

Pages | 145-152 |

Number of pages | 8 |

State | Published - Dec 1 2009 |

Event | 12th International Conference on Martensitic Transformations, ICOMAT-08 - Santa Fe, NM, United States Duration: Jun 29 2008 → Jul 5 2008 |

### Other

Other | 12th International Conference on Martensitic Transformations, ICOMAT-08 |
---|---|

Country | United States |

City | Santa Fe, NM |

Period | 6/29/08 → 7/5/08 |

### Fingerprint

### Keywords

- Compatibility
- Hysteresis
- NiTi
- TEM
- Twinning

### Cite this

_{50}Ni

_{50-x}Pd

_{x}alloys with special lattice parameters. In

*Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08*(pp. 145-152)

**TEM investigation of microstructures in low-hysteresis Ti _{50}Ni_{50-x}Pd_{x} alloys with special lattice parameters.** / Delville, Remi; Schryvers, Dominique; Zhang, Zhiyong; Kasinathan, Shaktivel; James, Richard D.

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

_{50}Ni

_{50-x}Pd

_{x}alloys with special lattice parameters. in

*Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08.*pp. 145-152, 12th International Conference on Martensitic Transformations, ICOMAT-08, Santa Fe, NM, United States, 6/29/08.

_{50}Ni

_{50-x}Pd

_{x}alloys with special lattice parameters. In Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08. 2009. p. 145-152

}

TY - GEN

T1 - TEM investigation of microstructures in low-hysteresis Ti 50Ni50-xPdx alloys with special lattice parameters

AU - Delville, Remi

AU - Schryvers, Dominique

AU - Zhang, Zhiyong

AU - Kasinathan, Shaktivel

AU - James, Richard D

PY - 2009/12/1

Y1 - 2009/12/1

N2 - A clear relationship between the hysteresis of shape memory alloys and the middle eigenvalue of their transformation stretch tensor (λ2) has recently been demonstrated experimentally and theoretically. As λ2 gets closer to 1, the geometric: compatibility between austenite and martensite increases as predicted in the geometric nonlinear theory of martensite (GNLTM)[1] and leads to a drop in hysteresis. Changes in microstructure are investigated by conventional transmission electron microscopy and electron diffraction for the Ti50Ni50-xPdx system over a range of compositions around the compatibility condition. Alloys sitting far enough above λ2 = 1, i.e. x>20, show a common microstructure for SMAs, consisting of parallel bands of martensite twinned along the {111} type I lattice invariant shear (LIS). This microstructure changes gradually as we tune the composition to approach the compatibility condition. The twinning ratio of martensite plates decreases until the plates become a single variant. The banded morphology is replaced by an apparent random mosaic of twinless martensite plates where self-accommodation seems to play an important role. In addition the in-situ growth of martensite in the austenite near the compatibility condition was observed and showed exact austenite-martensite interfaces along the predicted habit planes.

AB - A clear relationship between the hysteresis of shape memory alloys and the middle eigenvalue of their transformation stretch tensor (λ2) has recently been demonstrated experimentally and theoretically. As λ2 gets closer to 1, the geometric: compatibility between austenite and martensite increases as predicted in the geometric nonlinear theory of martensite (GNLTM)[1] and leads to a drop in hysteresis. Changes in microstructure are investigated by conventional transmission electron microscopy and electron diffraction for the Ti50Ni50-xPdx system over a range of compositions around the compatibility condition. Alloys sitting far enough above λ2 = 1, i.e. x>20, show a common microstructure for SMAs, consisting of parallel bands of martensite twinned along the {111} type I lattice invariant shear (LIS). This microstructure changes gradually as we tune the composition to approach the compatibility condition. The twinning ratio of martensite plates decreases until the plates become a single variant. The banded morphology is replaced by an apparent random mosaic of twinless martensite plates where self-accommodation seems to play an important role. In addition the in-situ growth of martensite in the austenite near the compatibility condition was observed and showed exact austenite-martensite interfaces along the predicted habit planes.

KW - Compatibility

KW - Hysteresis

KW - NiTi

KW - TEM

KW - Twinning

UR - http://www.scopus.com/inward/record.url?scp=77957869011&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=77957869011&partnerID=8YFLogxK

M3 - Conference contribution

SN - 9780873397452

SP - 145

EP - 152

BT - Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08

ER -