ESOMAT 2009, 02004 (2009)
DOI: 10.1051/esomat/200902004

3D FIB/SEM study of Ni₄Ti₃ precipitates in Ni-Ti alloys with different thermal-mechanical histories

S. Cao¹, M. Nishida², Ch. Somsen³, G. Eggeler³ and D. Schryvers<sup>1

1</sup>  EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium
²  Department of Engineering Sciences for Electronics and Materials, Kyushu University, Kasuga 816-8580, Japan
³  Institute for Materials, Ruhr University Bochum, D-44780 Bochum, Germany

Shanshan.Cao@ua.ac.be

Published online: 1 September 2009

Abstract
The three-dimensional size, morphology and distribution of Ni₄Ti₃ precipitates growing in binary Ni-rich Ni-Ti alloys have been investigated via a slice & view procedure in a Dual-Beam FIB/SEM system, in order to better understand their influence on the B2 to B19’ martensitic transformation. In the present work, both a stress-free Ni_50.8Ti_49.2 alloy with all four variants of precipitates and a compressed Ni₅₁Ti₄₉ alloy with aligned precipitates in one family were studied. The Ni₄Ti₃ precipitates reach a volume fraction of 9.6% in the reconstructed region of the stressfree alloy and 4.3% in the compressed one. In both cases, the mean volume, specific surface area, sphericity and aspect ratio of the precipitates are calculated and the Pair Distribution Functions of the precipitates are obtained. It is shown that most precipitates in the stress-free sample grow larger and have a more lenticular shape, while those in the compressed sample are more cylindrical. Deviations from these ideal shapes reveal internal steps in the stress-free sample and lamellae formation in the compressed one.

© Owned by the authors, published by EDP Sciences 2009