Surface-induced structural transformations in titanium nanowires

Bibliographic Details
Main Author:	Cheerkapally , Raghavender P.
Language:	English
Published:	University of Cincinnati / OhioLINK 2013
Subjects:	Mechanics molecular dynamics simulation embedded-atom method titanium nanowires surface effects phase transformations nudged elastic band method
Online Access:	http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384869599

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spelling	ndltd-OhioLink-oai-etd.ohiolink.edu-ucin13848695992021-08-03T06:20:37Z Surface-induced structural transformations in titanium nanowires Cheerkapally , Raghavender P. Mechanics molecular dynamics simulation embedded-atom method titanium nanowires surface effects phase transformations nudged elastic band method <p>Nanowires have a wide range of applications in nanotechnology and have a great technical importance due to their unique properties and structure. The material properties of the nanowires are significantly influenced by the surface atoms due to the high surface to volume ratio at the nanoscale. A fundamental understanding of the surface effects at the nanoscale is necessary to study the characteristics and properties of the nanowires. </p><p>In this work, molecular dynamics simulations are used to demonstrate the surface stress driven phase transformations in titanium nanowires. The surface-induced stress plays a critical role for the phase transformation of nanowires, and when combined with factors such as temperature and surface orientations, can lead to the so-called pseudoelasticity or shape memory effects in Ti. The study is focused on the behavior of HCP metal nanowires and structural transformations at the nanoscale.</p><p>Transformations leading from two initial HCP orientations of 〈11-20〉 and 〈1-100〉 of the Ti nanowires are discussed. Ti nanowires with an HCP α phase and initial orientation of 〈11-20〉 in the axial direction, spontaneously transforms to a BCC phase with an axial orientation of 〈100〉 with {110} surfaces, on relaxation at 0 K. Upon heating at a higher temperature, the BCC phase transforms to an FCC phase, which on tensile loading and subsequent unloading shows shape memory effects between FCC orientations. On the other hand, Ti nanowires with HCP phase and initial orientation of 〈1-100〉 in the axial direction, spontaneously transforms to an FCC phase with an axial orientation of 〈100〉 with {-110}/{001} surfaces, on relaxation at 0 K. In this case, a stacking fault is formed in the axial direction and as a result, no further transformation is possible upon heating or tensile loading. However, the stacking fault can be avoided by using an odd number of atomic layers but no significant transformation is noticed upon heating or tensile loading.</p><p>The transition pathways are also studied by the nudged elastic band (NEB) method using the initial and final states. The NEB method is used to find the minimum energy paths for the phase transformations. A set of intermediate images between the initial and final states are interpolated linearly by using the quenched velocity Verlet (QVV) algorithm to find the minimum energy path (MEP) of the transformations. The MEP for the phase transformations of HCP 〈11-20〉 and HCP 〈1-100〉 nanowires to BCC 〈100〉/{110} and FCC 〈100〉/{-110}{001} nanowires respectively have been plotted. The MEPs for the spontaneous phase transformation at 0 K for smaller width nanowires, follow a lower energy path compared to the initial potential energy. But nanowires with a larger cross-sectional width require additional thermal energy for the phase transformation to be complete, and the resulting activation energy barrier can be found using the NEB method.</p> 2013 English text University of Cincinnati / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384869599 http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384869599 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.
collection	NDLTD
language	English
sources	NDLTD
topic	Mechanics molecular dynamics simulation embedded-atom method titanium nanowires surface effects phase transformations nudged elastic band method
spellingShingle	Mechanics molecular dynamics simulation embedded-atom method titanium nanowires surface effects phase transformations nudged elastic band method Cheerkapally , Raghavender P. Surface-induced structural transformations in titanium nanowires
author	Cheerkapally , Raghavender P.
author_facet	Cheerkapally , Raghavender P.
author_sort	Cheerkapally , Raghavender P.
title	Surface-induced structural transformations in titanium nanowires
title_short	Surface-induced structural transformations in titanium nanowires
title_full	Surface-induced structural transformations in titanium nanowires
title_fullStr	Surface-induced structural transformations in titanium nanowires
title_full_unstemmed	Surface-induced structural transformations in titanium nanowires
title_sort	surface-induced structural transformations in titanium nanowires
publisher	University of Cincinnati / OhioLINK
publishDate	2013
url	http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384869599
work_keys_str_mv	AT cheerkapallyraghavenderp surfaceinducedstructuraltransformationsintitaniumnanowires
_version_	1719435154879938560

Surface-induced structural transformations in titanium nanowires

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