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Structural refinement of neutron powder diffraction data of two-stage martensitic phase transformations in Ti50.75Ni47.75Fe1.50 shape memory alloy

Published online by Cambridge University Press:  01 March 2012

Husin Sitepu
Husin Sitepu*
Affiliation:
Crystallography Laboratory, Virginia Tech, Blacksburg, Virginia 24061, USA and Prince Sultan University, P.O. Box 66833, Riyadh 11586, Saudi Arabia
*
Electronic mail: sitepu@vt.edu
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Abstract

Transformation behaviors of the technologically important polycrystalline Ti50.75Ni47.75Fe1.50 shape memory alloy were investigated using differential scanning calorimeter (DSC) and powder diffraction techniques. DSC revealed that there are two-stage (i.e., cubic→trigonal→monoclinic) martensitic phase transformations on cooling and a one-step transformation (monoclinic→cubic) on heating. In situ structural refinement of cubic→trigonal→monoclinic on cooling was carried out using the D1A high-resolution neutron powder diffractometer at the Institut Laue-Langevin Neutrons for Science in Grenoble, France. Results showed that the phases involved during the phase transition are consistent with the differential scanning calorimeter cooling curve, and the refined crystal structure parameters obtained from Rietveld refinements with the generalized spherical harmonic description agreed reasonably well with X-ray single-crystal data. Subsequently, a combined neutron and synchrotron structural refinement for each phase was conducted because the trial refinements initially using only the synchrotron data of trigonal phase yielded a false minimum with a somewhat high goodness-of-fit χ2. Results obtained from the combined neutron and synchrotron data of the cubic, trigonal, and monoclinic phases show that the same minimum goodness-of-fit indices were always obtained.

Keywords

neutron powder diffractiongeneralized spherical harmonicshape memory alloyTi-Nimartensitic transformation
Type
Technical Articles
Information
Powder Diffraction , Volume 22 , Issue 3 , September 2007 , pp. 209 - 218
Copyright
Copyright © Cambridge University Press 2007

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