Berlin 2005 – scientific programme
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M: Metallphysik
M 32: Poster TU B (Symposium Tomographic Methods in Materials Research M-32.32-55)
M 32.31: Poster
Monday, March 7, 2005, 14:30–16:30, Poster TU B
Martensitic transformation behavior of compression aged Ni-rich NiTi shape memory alloys — •J. Michutta1, Ch. Somsen1, A. Dlouhy2, K. Neuking1, and G. Eggeler1 — 1Institute of Materials Science, Ruhr-University Bochum, 44780 Germany — 2Institute of Physics of Materials, Zizkova 22, 61662 Brno, Czech Republic
In the present study we investigate the martensitic transformation behavior in Ni-Ti single crystals with a nomin al Ni content of 50.8at.% aged under compression of 50MPa in [111]-direction for aging times from 2ks up to 360ks at 550∘C. The martensitic transformation behavior of the compression aged single crystals is mainly characterize d by differential scanning calorimetry (DSC) and in-situ transmission electron microscopy (TEM) on cooling the sa mples. Compression aging at 550∘C in [111]-direction leads for all investigated aging times to the growth of only one family of Ni4Ti3 precipitates. In order to reduce internal stresses the Ni4Ti3 precipitates grow in an autoc atalytic process resulting in B2-type channels in between the precipitates. On cooling three peaks are present in the DSC charts, more distinct for the longer aging times from 16ks up to 360ks. In-situ TEM shows that the first peak on cooling is attributed to a martensitic transformation of the high temperature B2-phase to the martensiti c R-phase starting at the particle matrix interface all over the sample. In contrast the second peak is associate d with the formation of B19′ in favorite regions of the single crystal appearing in a burst like event on cooling in some channels. On further cooling from this transformed channels the martensitic B19′-phase growth, which exp lains the third peak in the DSC-measurements.