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

Remi Delville, Dominique Schryvers, Zhiyong Zhang, Shaktivel Kasinathan, Richard D James

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

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.

Original languageEnglish (US)
Title of host publicationProceedings of the International Conference on Martensitic Transformations, ICOMAT-08
Pages145-152
Number of pages8
StatePublished - Dec 1 2009
Event12th International Conference on Martensitic Transformations, ICOMAT-08 - Santa Fe, NM, United States
Duration: Jun 29 2008Jul 5 2008

Publication series

NameProceedings of the International Conference on Martensitic Transformations, ICOMAT-08

Other

Other12th International Conference on Martensitic Transformations, ICOMAT-08
CountryUnited States
CitySanta Fe, NM
Period6/29/087/5/08

Keywords

  • Compatibility
  • Hysteresis
  • NiTi
  • TEM
  • Twinning

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    Delville, R., Schryvers, D., Zhang, Z., Kasinathan, S., & James, R. D. (2009). TEM investigation of microstructures in low-hysteresis Ti 50Ni50-xPdx alloys with special lattice parameters. In Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08 (pp. 145-152). (Proceedings of the International Conference on Martensitic Transformations, ICOMAT-08).