| Numéro |
J. Phys. IV France
Volume 112, October 2003
|
|
|---|---|---|
| Page(s) | 643 - 646 | |
| DOI | https://doi.org/10.1051/jp4:2003965 | |
J. Phys. IV France 112 (2003) 643
DOI: 10.1051/jp4:2003965
A neutron diffraction study of the martensitic transformations in aged Ni-rich NiTi alloys
H. Sitepu1, W.W. Schmahl1, G. Eggeler2, J. Khalil Allafi2 and D.M. Többens31 Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
2 Institut für Werkstoffe, Ruhr-Universität Bochum, 44780 Bochum, Germany
3 Hahn-Meitner-Institut (HMI), 14109 Berlin, Germany
Abstract
The transformation of a Ni-rich NiTi alloy of nominal composition 50.7 atomic percent nickel which was solution annealed,
water quenched and aged at 500 °C for 20 hours was investigated. The material shows a two-step transition on cooling with
differential scanning calorimetry peaks at 180 °C and 7 °C. On heating, a single peak occurs at 43 °C. The aging leads to
the formation of Ni
4Ti
3 precipitates in the microstructure, and in the presence of the precipitates the martensitic transformation occurs from the
cubic B2 phase via the R-phase to B19
' martensite. However, the first peak on cooling is not due to the formation of R-phase alone. Below the peak temperature,
R-phase is present along with some B19
' and with residual B2 and the precipitates. The second peak is related to the transformation of R-phase and B2 to B19
'. This result confirms our earlier conclusions which were obtained for the same alloy aged at 400 °C for 20 hours.
© EDP Sciences 2003