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Effects of Grain Size on Phase Transition Behavior of Nanocrystalline Shape Memory Alloys

le 28 mai 2015

Le Professeur Qingping SUN du Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, animera un séminaire du LMT à l'ENS de Cachan.

Sun QingPing - Hong Kong University of Science & Technology

Sun QingPing - Hong Kong University of Science & Technology

This conference concerns one of Sun Qingping research interests : Shape memory alloy single and polycrystals.

We report recent advances in the experimental and theoretical study of grain size (GS) effects on the thermal and mechanical properties of nanostructured NiTi polycrystalline shape memory alloy (SMA).

It is shown that the material internal length scales of GS and interface thickness have great impact on the phase transition behavior of solids. 
When GS < 60 nm, the superelastic stress-strain hysteresis loop area (H) of the polycrystal decreases rapidly with GS and tends to vanish as GS approaches 10 nanometers.

At the same time, the temperature dependence of the transition stress also decreases with GS and eventually approaches zero, leading to a wide superelastic temperature window and breakdown of the Clausius-Claperyon relationship.

Grain size and nanocrystallization

Rate dependence of the stress-strain responses is significantly reduced and the cyclic stability of the material is improved by the nanocrystallization.

It is proposed that the emergence of such significant changes in the behavior of the material with GS reduction originates from the large increase in the area-to-volume ratios of the nanometer-thick interfaces (grain boundary and Austenite-Martensite (A-M) interface) in the polycrystal.

In particular, with GS reduction, interfacial energy terms will gradually become dominant over the bulk energy of the crystallite, eventually bring fundamental changes in the phase transition responses of the material.
Type :
Séminaires - conférences
Lieu(x) :
Campus de Cachan
Amphi e-média
Bâtiment Léonard De Vinci de - ENS Cachan
61, avenue du Président Wilson 94230 Cachan
Plan d'accès

Sun QingPing

Agenda des séminaires 2015

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