On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys

0354828 - ÚFM 2011 RIV GB eng J - Journal Article
Simon, T. - Kröger, A. - Somsen, Ch. - Dlouhý, Antonín - Eggeler, G.
On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys.
Acta Materialia. Roč. 58, č. 5 (2010), s. 1850-1860. ISSN 1359-6454. E-ISSN 1873-2453
R&D Projects: GA ČR GA106/09/1913
Institutional research plan: CEZ:AV0Z20410507
Keywords : NiTi * Martensitic transformations * Dislocation multiplication mechanism * Martensite variants * Dislocations
Subject RIV: BM - Solid Matter Physics ; Magnetism
Impact factor: 3.781, year: 2010

In situ and post-mortem diffraction contrast transmission electron microscopy (TEM) was used to study the multiplication of dislocations during a thermal martensitic forward and reverse transformation in a NiTi shape memory alloy single crystal. An analysis of the elongated dislocation loops which formed during the transformation was performed. It is proposed that the stress field of an approaching martensite needle activates an in-grown dislocation segment and generates characteristic narrow and elongated dislocation loops which expand on {1 1 0}B2 planes parallel to {0 0 1}B190 compound twin planes. The findings are compared with TEM results reported in the literature for NiTi and other shape memory alloys. It is suggested that the type of dislocation multiplication mechanism documented in the present study is generic and that it can account for the increase in dislocation densities during thermal and stress-induced martensitic transformations in other shape memory alloys.
Permanent Link: http://hdl.handle.net/11104/0193743