Impact of Heat Treatment Environment of Microstructure and Transformation Path in NiTi Shape Memory Alloy

0376020 - ÚFM 2012 RIV CZ eng C - Conference Paper (international conference)
Kuběnová, Monika - Zálešák, Jakub - Čermák, Jiří - Barták, Tomáš - Dlouhý, Antonín
Impact of Heat Treatment Environment of Microstructure and Transformation Path in NiTi Shape Memory Alloy.
METAL 2011 Conference Proceedings. Ostrava: TANGER, spol. s r.o., 2011, paper no. 1031. ISBN 978-80-87294-22-2.
[METAL 2011 /20./. Brno (CZ), 18.05.2011-20.05.2011]
R&D Projects: GA ČR GA106/09/1913
Institutional research plan: CEZ:AV0Z20410507
Keywords : heat treatment atmosphere * nickel-rich NiTi shape memory alloys * heat flow
Subject RIV: JG - Metallurgy

We report results of differential scanning calorimetry (DSC) experiments in which heat flow (T) from and to Ti-50.9at%Ni shape memory samples was recorded during the temperature scan through a B2  B19’ transformation range. Prior to the DSC experiments, the samples were separately annealed in evacuated quartz capsules containing different hydrogen and helium mixtures with an overall filling pressure of 900 mbar. The quartz tubes containing the annealed samples were subsequently quenched into cold water. After quenching, the capsules were opened, martensitic transformations were investigated by DSC and the microstructure of the samples was assessed by transmission electron microscopy (TEM). Annealing in the mixtures with an increasing partial pressure of hydrogen led to a considerable drop in the latent heat associated with the B2  B19’ martensitic transformation. Results obtained using TEM suggest that hydrogen may function as a catalytic substance that accelerates the long range ordering of Ni atoms in early stages of Ni4Ti3-phase precipitation. The selected area diffraction study focused on patterns in 100B2 and 110B2 zones and provided evidence for diffuse scattering due to spatial modulations of the lattice constant. These variations in the background electron intensities might be related to a precursor of Ni4Ti3 phase in its early state of formation.
Permanent Link: http://hdl.handle.net/11104/0006938