Original title: AN INTERPLAY BETWEEN HEAT TREATMENT CONDITIONS AND B2 <-> B19 ' TRANSFORMATION IN Ni-Ti SHAPE MEMORY ALLOYS
Authors: Kuběnová, Monika ; Zálešák, Jakub ; Čermák, Jiří ; Dlouhý, Antonín
Document type: Papers
Conference/Event: METAL 2010 -International metallurgical and materials conference /19./, Rožnov pod Radhoštěm (CZ), 20100518
Year: 2010
Language: eng
Abstract: This study investigates the influence of a heat treatment atmosphere on multistage martensitic transformations in a Ti-50.9at% Ni shape memory alloy. Evacuated quartz tubes were filled with hydrogen while the hydrogen partial pressure was carefully controlled in each experiment. The encapsulated specimens were subjected to heat treatments consisting of annealing and aging. After the heat treatment, the path of martensitic transformation was investigated using differential scanning calorimetry (DSC). On cooling, martensite initial temperatures decrease with the increasing partial pressure of hydrogen applied during the heat treatment. Moreover, the formation of martensite phase may not take place for partial pressures that exceed a certain limit. On the other hand, two-and multiple-step B2/R/B19' martensitic transformations are observed in specimens heat treated at lower hydrogen pressures. Results obtained using transmission electron microscopy (TEM) clearly show that the size of Ni4Ti3 precipitates becomes smaller in alloys that were heat treated at higher hydrogen pressures. The results are discussed in terms of a chain of events. It is suggested that diffusion of hydrogen into the specimen during the annealing step first influences the nucleation of the Ni4Ti3 phase. The sizes and distribution of the Ni4Ti3 precipitates than control the characteristics of B2/B19' transformation.
Keywords: differential scanning calorimetry; Heat treatment atmosphere; nickel-rich NiTi shape memory alloys; transmission electron microscopy
Project no.: CEZ:AV0Z2041904 (CEP)
Host item entry: METAL 2010: 19TH INTERNATIONAL METALLURGICAL AND MATERIALS CONFERENCE, ISBN 978-80-87294-17-8

Institution: Institute of Physics of Materials AS ČR (web)
Document availability information: Fulltext is available at the institute of the Academy of Sciences.
Original record: http://hdl.handle.net/11104/0279749

Permalink: http://www.nusl.cz/ntk/nusl-371437


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