Document 
Eur. Phys. J. Special Topics 158, 59-65 (2008)
DOI: 10.1140/epjst/e2008-00654-6
Powder metallurgy technology of NiTi shape memory alloy
J.M. Dutkiewicz1, W. Maziarz1, T. Czeppe1, L. Litynska1, W.K. Nowacki2, S.P. Gadaj2, J. Luckner2 and E.A. Pieczyska21 Institute of Metallurgy and Materials Science of the Polish Academy of Sciences, ul. Reymonta 25, 30-059 Kraków, Poland
2 Institute of Fundamental Technological Problems of the Polish Academy of Sciences, 00-049 Warszawa ul. Swietokrzyska 21, Poland
(Published online: 1 May 2008)
Abstract
Powder metallurgy technology was elaborated for
consolidation of shape memory NiTi powders. The shape memory alloy was
compacted from the prealloyed powder delivered by Memry SA. The powder shows
= 10°C and
= -34°C as results from DSC
measurements. The samples were hot pressed in the as delivered spherical
particle's state. The hot compaction was performed in a specially
constructed vacuum press, at temperature of 680°C and pressure of 400 MPa. The alloy powder was encapsulated in copper capsules prior to hot
pressing to avoid oxidation or carbides formation. The alloy after hot
vacuum compaction at 680°C (i.e. within the B2 NiTi stability range)
has shown similar transformation range as the powder. The porosity of
samples compacted in the as delivered state was only 1%. The samples
tested in compression up to
= 0.06 have shown partial
superelastic effect due to martensitic reversible transform- ation which
started at the stress above 300 MPa and returned back to
= 0.015 after unloading. They have shown also a high ultimate compression
strength of 1600 MPa. Measurements of the samples temperature changes during
the process allowed to detect the temperature increase above 12°C for
the strain rate 10-2 s-1 accompanied the exothermic martensite
transformation during loading and the temperature decrease related to the
reverse endothermic transformation during unloading.
© EDP Sciences, Springer-Verlag 2008