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Metals 2015, 5(2), 530-546; doi:10.3390/met5020530

An in situ Study of NiTi Powder Sintering Using Neutron Diffraction

1,2,* , 3,4
and
1,*
1
Department of Chemical and Materials Engineering, the University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
2
State Key Laboratory of Porous Metal Materials, Northwest Institute for Nonferrous Metal Research, Xi'an 710016, Shaanxi, China
3
Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia
4
Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-Shirane Tokai-mura, Naka-gun, Ibaraki-ken 319-1195, Japan
*
Authors to whom correspondence should be addressed.
Academic Editor: Hugo F. Lopez
Received: 27 February 2015 / Revised: 23 March 2015 / Accepted: 27 March 2015 / Published: 3 April 2015
(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)
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Abstract

This study investigates phase transformation and mechanical properties of porous NiTi alloys using two different powder compacts (i.e., Ni/Ti and Ni/TiH2) by a conventional press-and-sinter means. The compacted powder mixtures were sintered in vacuum at a final temperature of 1373 K. The phase evolution was performed by in situ neutron diffraction upon sintering and cooling. The predominant phase identified in all the produced porous NiTi alloys after being sintered at 1373 K is B2 NiTi phase with the presence of other minor phases. It is found that dehydrogenation of TiH2 significantly affects the sintering behavior and resultant microstructure. In comparison to the Ni/Ti compact, dehydrogenation occurring in the Ni/TiH2 compact leads to less densification, yet higher chemical homogenization, after high temperature sintering but not in the case of low temperature sintering. Moreover, there is a direct evidence of the eutectoid decomposition of NiTi at ca. 847 and 823 K for Ni/Ti and Ni/TiH2, respectively, during furnace cooling. The static and cyclic stress-strain behaviors of the porous NiTi alloys made from the Ni/Ti and Ni/TiH2 compacts were also investigated. As compared with the Ni/Ti sintered samples, the samplessintered from the Ni/TiH2 compact exhibited a much higher porosity, a higher close-to-total porosity, a larger pore size and lower tensile and compressive fracture strength. View Full-Text
Keywords: NiTi; powder sintering; dehydrogenation; neutron diffraction NiTi; powder sintering; dehydrogenation; neutron diffraction
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Chen, G.; Liss, K.-D.; Cao, P. An in situ Study of NiTi Powder Sintering Using Neutron Diffraction. Metals 2015, 5, 530-546.

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