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Stress-induced phase transformation and pseudo-elastic/pseudo-plastic recovery in intermetallic Ni–Al nanowires
Dear friends,
I want to share our recent research work on NiAl nanowire, which is published in Nanotechnology, IOP publishing. The abstract of the paper is given below. Further details can be found at " 2009 Nanotechnology 20 295705 (9pp) doi: 10.1088/0957-4484/20/29/295705"
Abstract.
Extensive molecular dynamics (MD) simulations have been performed in a B2-NiAl
nanowire using an embedded atom method (EAM) potential. We show a stress induced
-centered-tetragonal (BCT) phase transformation and a novel temperature and cross-section dependent
pseudo-elastic/pseudo-plastic recovery from such an unstable BCT phase with a recoverable strain
of ~30%
as compared to 5–8% in polycrystalline materials. Such a temperature and cross-section
dependent pseudo-elastic/pseudo-plastic strain recovery can be useful in various
interesting applications of shape memory and strain sensing in nanoscale devices.
Effects of size, temperature, and strain rate on the structural and mechanical
properties have also been analyzed in detail. For a given size of the nanowire
the yield stress of both the B2 and the BCT phases is found to decrease with
increasing temperature, whereas for a given temperature and strain rate the yield
stress of both the B2 and the BCT phase is found to increase with increase in
the cross-sectional dimensions of the nanowire. A constant elastic modulus of
~80 GPa of the B2 phase is observed in the temperature range of 200–500 K for nanowires of
cross-sectional dimensions in the range of 17.22–28.712 Å, whereas the elastic modulus of
the BCT phase shows a decreasing trend with an increase in the temperature.
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Superplasticity in intermetallic NiAl nanowires
Recently a paper on "Superplasticity in intermetallic NiAl nanowires via atomistic simulations" has been published in Materials Letters, Volume 64, Issue 7, 15 April 2010, Pages 879-881 by Vijay Kumar Sutrakar and D Roy Mahapatra.
The abstract of the paper is given below:
Abstract
A novel superplastic deformation in an intermetallic B2-NiAl nanowire of cross-sectional dimensions of
20 Å with failure strain as high as 
700% at 700 K temperature is reported. The minimum temperature under which the superplasticity has been observed is around 0.36 Tm, which is much lower than 0.5 Tm (Tm = melting temperature i.e. 1911 K for bulk B2-NiAl). Superplasticity is observed due to transformation from crystalline phase to amorphous phase after yielding of the nanowire.
Copyright © 2010 Elsevier B.V. All rights reserved. ScienceDirect® is a registered trademark of Elsevier B.V.
Asymmetry in Structural and Thermo-Mechanical Response of NiAl
Recently a paper titled as "Asymmetry
in Structural and Thermo-Mechanical behavior of Intermetallic Ni-Al
Nanowire under Tensile/Compressive Loading: A Molecular Dynamics Study" has been published in Intermetallics by Vijay Kumar Sutrakar and D Roy Mahapatra.
The Abstract of the paper is given below.
Abstract:
The asymmetric stress–strain behavior under tension/compression in an initial
100
B2-NiAl nanowire is investigated considering two different surface configurations i.e., 
100
/(0 1 0) (0 0 1) and 
100
/(0
100
0.30.
−0.12.
1 1) (0 −1 1). This behavior is attributed to two different deformation
mechanisms namely a slip dominated deformation under compression and a known twinning dominated deformation under tension. It is also shown
that B2 → BCT (body-centered-tetragonal) phase transformation under
tensile loading is independent of the surface configurations for an
initial
oriented NiAl nanowire. Under tensile loading, the nanowire undergoes a
stress-induced martensitic phase transformation from an initial B2
phase to BCT phase via twinning along {110} plane with failure strain
of
On the other hand, a compressive loading causes failure of these
nanowires via brittle fracture after compressive yielding, with a
maximum failure strain of
Such brittle fracture under compressive loading occurs via slip along
{110} plane without any phase transformations. Softening/hardening
behavior is also reported for the first time in these nanowires under tensile/compressive loadings, which cause asymmetry in their yield
strength behavior in the stress–strain space. Result shows that a sharp
increase in energy with increasing strain under compressive loading
causes hardening of the nanowire, and hence, gives improved yield
strength as compared to tensile loading.
Copyright © 2010 Elsevier B.V. All rights reserved. ScienceDirect® is a registered trademark of Elsevier B.V.