J. Phys. IV France
Volume 112, October 2003
Page(s) 1039 - 1042

J. Phys. IV France
112 (2003) 1039
DOI: 10.1051/jp4:20031059

Morphological and crystallographic aspects of Cl1 $_{\rm b}$-type precipitates nucleated in martensitic and parent phase matrices in Ti-rich Ti-Pd shape memory alloys

V.C. Solomon and M. Nishida

Kumamoto University, Deparlment of Materials Science and Engineering, Graduate School of Science and Technology, 2-39-1 Kurokami, Kumamoto 860-8555, Japan

Ti 2Pd phase with Cll $_{\rm b}$-type structure which precipitates in Ti-rich Ti-Pd shape memory alloys may nucleate either in martensitic phase or parent phase depending upon thermal treatment conditions, since the transformation temperatures are around 800 K. In the alloy aged above Af, three Clin-type precipitate variants are always observed by TEM. The orientation relationship between those three variants and the Bl9 structure, which was transformed from B2 structure after the precipitation, is as follows: Variant I (001) $_{\rm Ti2Pd}$//(10 $\bar{1}$) $_{\rm Bl9}$; Variant II (001) $_{\rm Ti2Pd}$//(001) $_{\rm B19}$; Variant III (001) $_{\rm Ti2Pd}$/(010) $_{\rm B19}$. The shape of the precipitates was deduced to be disk-like and/or elliptic. On the other hand, only the variants I and II are observed when the precipitates are nucleated in martensitic phase. Since the difference between the lattice spacing of (010) $_{\rm BI9}$ and (001)/3 $_{\rm Ti2Pd}$ is about 20%, the formation of a third variant in the martensitic matrix is energetically unfavorable.

© EDP Sciences 2003