Why is twinning (and not slip) a favoured mechanism of deformation in shape memory alloys?
May I recommend the University of Illinois at Urbana-Champaign dissertation "Dislocation Slip and Twinning Stress in Shape Memory Alloys - Theory and Experiments" by Jifeng Wang?
Hi,
in the following paper from 2016 the TIE-effect (Twinning Induced Elasticity) in NiTi was investigated:
Twinning-Induced Elasticity in NiTi Shape Memory Alloys
Thorsten Birk, Somjeet Biswas, Jan Frenzel, Gunther Eggeler
SPECIAL ISSUE: RESEARCH ON BIOMEDICAL SHAPE MEMORY ALLOYS, INVITED PAPERFirst Online: 17 March 2016
DOI: 10.1007/s40830-016-0064-1
http://link.springer.com/article/10.1007/s40830-016-0064-1#Sec15
Maybe this contains also some more information about your question.
Best regards
Hi Santosh,
In general, the twinning boundary has lower energy than stacking fault or slip region. Which mechanism of deformation comes into being strongly depends on alloys constituents and structure state. During stress accommodation by slip one or several lattice planes are shifted only by integral numbers of interatomic distances. Slip is realized by moving of dislocations and the lattice in slip region is identical with another lattices in its vicinity.
Accommodation by twinning is realized by moving of partial dislocations in region of twinning plane which means that shifting of atomic layers occur in manner one after one and the shifting of each plane is on distance less than interatomic distance. The atomic bonds are not broken instead of slip. Lattice in twinned region is then mirror image of lattice in untwinned region.
In shape memory alloys there is important parameter called critical resolved shear stress (CRSS). For shape memory effect we need lower CRSS for twinning than for slip nucleation of martensite. For more details I recommend you attached paper.
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