Received: from mx05.ecn.purdue.edu (mx05.ecn.purdue.edu [128.46.88.3]) by mailbag.ecn.purdue.edu (8.14.4/8.14.4) with ESMTP id q3JErsZi017207 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Thu, 19 Apr 2012 10:53:54 -0400 (EDT) Received: from mailhub130.itcs.purdue.edu (mailhub130.itcs.purdue.edu [128.210.5.130]) by mx05.ecn.purdue.edu (8.14.4/8.14.4) with ESMTP id q3JErIVY017943 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Thu, 19 Apr 2012 10:53:18 -0400 Received: from WPPEXHUB01F.purdue.lcl (wppexhub01f.itap.purdue.edu [172.21.6.90]) by mailhub130.itcs.purdue.edu (8.14.4/8.14.4/mta-nopmx.smtp.purdue.edu) with ESMTP id q3JErIBH032439 for ; Thu, 19 Apr 2012 10:53:18 -0400 Received: from VPEXCH02.purdue.lcl ([169.254.2.132]) by WPPEXHUB01F.purdue.lcl ([::1]) with mapi; Thu, 19 Apr 2012 10:53:18 -0400 From: "Stacey, Lisa A" To: "'msepostdoc-list@ecn.purdue.edu'" Date: Thu, 19 Apr 2012 10:53:17 -0400 Subject: FW: Auto-discard notification Thread-Topic: Auto-discard notification Thread-Index: Ac0eN/T5ocAYvTHeRSGzeCGgZBar5gAA/1xA Message-ID: <92F872D971E7AA498CF64DD847E5594D89C36E8289@VPEXCH02.purdue.lcl> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: acceptlanguage: en-US x-perlmx-virus-scanned: Yes x-pmx-version: 5.5.9.388399 x-ecn-mailserver-origination: mailhub130.itcs.purdue.edu [128.210.5.130] x-ecn-mailserver-spamscanadvice: DoNotScan x-ecn-mailserver-virusscanned: by amavisd-new Content-Type: multipart/mixed; boundary="_002_92F872D971E7AA498CF64DD847E5594D89C36E8289VPEXCH02purdu_" MIME-Version: 1.0 --_002_92F872D971E7AA498CF64DD847E5594D89C36E8289VPEXCH02purdu_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Please see attached Seminar Reminder for today --_002_92F872D971E7AA498CF64DD847E5594D89C36E8289VPEXCH02purdu_ Content-Type: message/rfc822 Received: from mx05.ecn.purdue.edu (mx05.ecn.purdue.edu [128.46.88.3]) by mailbag.ecn.purdue.edu (8.14.4/8.14.4) with ESMTP id q3JEMvOj016300 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT); Thu, 19 Apr 2012 10:22:57 -0400 (EDT) Received: from mailhub131.itcs.purdue.edu (mailhub131.itcs.purdue.edu [128.210.5.131]) by mx05.ecn.purdue.edu (8.14.4/8.14.4) with ESMTP id q3JELs79013955 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT); Thu, 19 Apr 2012 10:21:54 -0400 Received: from WPPEXHUB03H.purdue.lcl (wppexhub03h.itap.purdue.edu [172.21.6.92]) by mailhub131.itcs.purdue.edu (8.14.4/8.14.4/mta-nopmx.smtp.purdue.edu) with ESMTP id q3JELs7L031887; Thu, 19 Apr 2012 10:21:54 -0400 Received: from VPEXCH02.purdue.lcl ([169.254.2.132]) by WPPEXHUB03H.purdue.lcl ([172.21.6.92]) with mapi; Thu, 19 Apr 2012 10:21:54 -0400 From: "Stacey, Lisa A" To: "'msefaculty-list@ecn.purdue.edu'" , "'msegradstudent-list@ecn.purdue.edu'" , "'msepostdoc-list@ecn.purdue.edu'" Date: Thu, 19 Apr 2012 10:21:53 -0400 Subject: REMINDER: 4/19/12 3:30 PM SEMINAR Ph.D. Final Exam-K. Vishnu Thread-Topic: REMINDER: 4/19/12 3:30 PM SEMINAR Ph.D. Final Exam-K. Vishnu Thread-Index: Ac0YsLPRhHemtB7KT32yv/i0pNboNQFhtXbg Message-ID: <92F872D971E7AA498CF64DD847E5594D89C36E8287@VPEXCH02.purdue.lcl> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: acceptlanguage: en-US x-perlmx-virus-scanned: Yes x-pmx-version: 5.5.9.388399 x-ecn-mailserver-origination: mailhub131.itcs.purdue.edu [128.210.5.131] x-ecn-mailserver-spamscanadvice: DoNotScan x-ecn-mailserver-virusscanned: by amavisd-new Content-Type: multipart/related; boundary="_004_92F872D971E7AA498CF64DD847E5594D89C36E8287VPEXCH02purdu_"; type="multipart/alternative" MIME-Version: 1.0 --_004_92F872D971E7AA498CF64DD847E5594D89C36E8287VPEXCH02purdu_ Content-Type: multipart/alternative; boundary="_000_92F872D971E7AA498CF64DD847E5594D89C36E8287VPEXCH02purdu_" --_000_92F872D971E7AA498CF64DD847E5594D89C36E8287VPEXCH02purdu_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable MATERIALS SCIENCE AND ENGINEERING SEMINAR Shape Memory in Nanostructured Metallic Alloys by Karthik Guda Vishnu Purdue Ph.D. Final Exam Advisor Professor A. Strachan ABSTRACT Materials with nano-scale dimensions show mechanical and structural propert= ies different to those at the macro scale and engineering their nano-struct= ure opens up potential avenues for designing materials tailored for a speci= fic application. This work is focused on shape memory materials, an importa= nt class of active materials with wide variety of applications in medical i= ndustry, aerospace and automobile industries, due to their two important pr= operties of super-elasticity and shape memory. These unique properties orig= inate from a solid-solid transformation called martensite transformation an= d the main objectives of this research are to i) study the atomic mechanism= s of the martensite transformation, ii) study the effect of nano-structure = on shape memory behavior and iii) computationally explore avenues through w= hich their performance is optimized. A combination of density functional th= eory (DFT) and molecular dynamics (MD) simulations is used to achieve this.= This approach gives an atomic level description and the effects of size, s= urfaces and interfaces are explicitly described. Detailed analysis of the a= tomic mechanisms of the martensite transformation in NiTi using DFT reveale= d a new phase transformation (B19=92=92) that sheds light on why the theore= tically predicted ground state (BCO) is not observed experimentally and tha= t the experimentally observed martensite phase (B19=92) can be stabilized b= y internal stresses. This finding is very important as the theoretically pr= edicted ground state does not allow for shape memory in nano-scale NiTi sam= ples. The size effects caused by the presence of free surfaces and the role of na= no-structure in martensite transformation have been investigated in thin Ni= Ti slabs. Surface energies of B2 phase (austenite), B19 (orthorhombic), B19= =92 (martensite) and the body centered orthorhombic phase (BCO) are calcula= ted using DFT. (110)B2 surfaces with in-plane atomic displacements stabiliz= e the austenite phase with respect to B19=92 and BCO, thus slabs with such = orientations are predicted to exhibit a decrease in martensite transition t= emperature with decreasing thickness. It has been predicted that a thicknes= s of 2 nm is critical for the transition to occur. The opposite trend is ob= served in slabs with atomic displacements along the surface normal; the pha= se transformation temperature increases with decreasing size. Finally, it has also been demonstrated via large scale molecular dynamics s= imulations that the austenite =96 martensite energy landscapes of NiAl base= d thermo-elastic shape memory superlattice structures can be engineered via= epitaxial integration. This allows for tuning their thermal hysteresis and= transition temperatures. This resulted in materials with very low thermal = hysteresis and with minimal degradation in phase transition strain thereby = making them ideal for actuating applications. Date: Thursday, April 19, 2012 Time: 3:30 P.M. Place: ARMS Room 1028 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100 --_000_92F872D971E7AA498CF64DD847E5594D89C36E8287VPEXCH02purdu_ Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable

<= span style=3D"font-size:14.0pt;line-height:150%">MATERIALS SCIENCE AND ENGI= NEERING

SEMINAR

 

Shape Memory in Nanostructured Metallic Alloys

 

by

 

Karthik Guda Vishnu

Purdue Ph.D. Final Exam

 

Advisor

Professor= A. Strachan

 

ABSTR= ACT

 

Materials with nano-scale dimensions show mechanical and structural pro= perties different to those at the macro scale and engineering their nano-st= ructure opens up potential avenues for designing materials tailored for a s= pecific application. This work is focused on shape memory materials, an imp= ortant class of active materials with wide variety of applications in medic= al industry, aerospace and automobile industries, due to their two importan= t properties of super-elasticity and shape memory. These unique properties = originate from a solid-solid transformation called martensite transformatio= n and the main objectives of this research are to i) study the atomic mecha= nisms of the martensite transformation, ii) study the effect of nano-struct= ure on shape memory behavior and iii) computationally explore avenues throu= gh which their performance is optimized. A combination of density functiona= l theory (DFT) and molecular dynamics (MD) simulations is used to achieve t= his. This approach gives an atomic level description and the effects of siz= e, surfaces and interfaces are explicitly described. Detailed analysis of t= he atomic mechanisms of the martensite transformation in NiTi using DFT rev= ealed a new phase transformation (B19=92=92) that sheds light on why the th= eoretically predicted ground state (BCO) is not observed experimentally and= that the experimentally observed martensite phase (B19=92) can be stabiliz= ed by internal stresses. This finding is very important as the theoreticall= y predicted ground state does not allow for shape memory in nano-scale NiTi= samples.

The size effects caused by the presence of free surfaces and the role of n= ano-structure in martensite transformation have been investigated in thin N= iTi slabs. Surface energies of B2 phase (austenite), B19 (orthorhombic), B1= 9=92 (martensite) and the body centered orthorhombic phase (BCO) are calcul= ated using DFT. (110)B2 surfaces with in-plane atomic displaceme= nts stabilize the austenite phase with respect to B19=92 and BCO, thus slab= s with such orientations are predicted to exhibit a decrease in martensite = transition temperature with decreasing thickness. It has been predicted tha= t a thickness of 2 nm is critical for the transition to occur. The opposite= trend is observed in slabs with atomic displacements along the surface nor= mal; the phase transformation temperature increases with decreasing size.

Finally, it has also been demonstrated = via large scale molecular dynamics simulations that the austenite =96 marte= nsite energy landscapes of NiAl based thermo-elastic shape memory superlatt= ice structures can be engineered via epitaxial integration. This allows for= tuning their thermal hysteresis and transition temperatures. This resulted= in materials with very low thermal hysteresis and with minimal degradation= in phase transition strain thereby making them ideal for actuating applica= tions.

 

= Date:   Thursday, April 19, 2012

Time:   3:30 P.M.

= Place:   ARMS Room 1028

 

 

 

Lisa Stacey

Secretary/Development Assistant

Purdue Uni= versity

School of Materials Engineering

765/494-4100

 

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