Ankündigung eines Vortrages von

Herrn  Dr. S. Egorov
St.-Petersburg University, St. Petersburg, Russia

über das Thema

Specific features of the relation between martensic transformations and shape memory effects in Ti-Ni alloys
am Montag, dem 9. Dezember 2002, 16 Uhr c.t., Hörsaal M 123 (Gebäude M)


In Ti-Ni-based alloys the features of the temperature kinetics of martensitic transformations (MT) and memory effects are systematically investigated. In alloys Ti52Ni47,5Fe0,5 and Ti52,5Ni47Fe0,5 with the help of in situ electric resistance measurements during a torsion experiments it is revealed, that under a stress there is an inhibition of the direct MT B2®R. The extent of this inhibition is very high and can not be explained only on the basis of the Klausius-Klapeiron equation. Besides, the action of the stress changes the sequence of MT from B2®R®B19’ to B2® B2 + B19’ ® R + B19’® B19’. This change gives rise to the appearance of some specific features in the temperature kinetics of the strain accumulation due to the MT at cooling. During heating up from a low-temperature state (B19’ phase) to the high-temperature state (B2 phase) the strain recovery occurs in such a way that first the strain change is due to twinning of the B19’ phase and then – to the B2®B19’ MT.

On the whole similar effects are obtained for the alloy Ti50,3Ni49,7 with the use of differential scanning calorimetry and dilatometry. In this case samples were tested in compression.

The in situ differential thermal analysis executed on a Ti53Ni47,5Fe0,5 tubular sample in a torsion experiment, as well as the other data, allows to make the following conclusions. First, there is no strict correspondence between the characteristic temperatures of the MT and those of the memory effects in Ti-Ni alloys, second, the stress changes the mechanisms of the memory effects.