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On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys / T. Simon in Acta materialia, Vol. 58 N° 5 (Mars 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1850–1860 Titre : On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys Type de document : texte imprimé Auteurs : T. Simon, Auteur ; A. Kröger, Auteur ; C. Somsen, Auteur Année de publication : 2011 Article en page(s) : pp. 1850–1860 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : NiTi  Martensitic  transformations  Dislocation  multiplication  mechanism  Martensite  variants  Dislocations Résumé : 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}B19′ 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. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008076 [article] On the multiplication of dislocations during martensitic transformations in NiTi shape memory alloys [texte imprimé] / T. Simon, Auteur ; A. Kröger, Auteur ; C. Somsen, Auteur . - 2011 . - pp. 1850–1860. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1850–1860 Mots-clés : NiTi  Martensitic  transformations  Dislocation  multiplication  mechanism  Martensite  variants  Dislocations Résumé : 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}B19′ 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. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008076