April 2013 - Msepostdoc-list

FW: SEMINAR REMINDER: M. Dubelman-PhD Final, Tue. 4/9/13, 9:00 am, HAMP 1113
by Stacey, Lisa A 09 Apr '13

09 Apr '13

Please see seminar reminder below (note the location in HAMP): MATERIALS SCIENCE AND ENGINEERING SEMINAR Domain Evolution in Lead-Free Thin Film Piezoelectric Ceramics By: Meredith E. Dubelman Ph.D. Final Examination Advisor: Prof. J. Blendell ABSTRACT Due to environmental and health concerns lead-free piezoelectric systems are currently being evaluated for use as replacements for lead-based ceramics. Sodium Bismuth Titanate, Na0.5Bi0.5TiO3 (NBT) - based materials offer possible alternatives. NBT is a perovskite-type, ABO3, compound and is ferroelectric at room temperature. It has a relatively high Curie temperature, a large remnant polarization, and a high coercive field at room temperature. NBT can be modified by additives, such as BaTiO3 (BT), to improve its properties further. NBT-xBT was originally reported to have a morphotropic phase boundary which lies at x = 0.06. The structure transforms from rhombohedral for x < 0.06 to tetragonal for x > 0.06. However, recent studies have shown that for some compositions NBT-xBT develop a relaxor phase at room temperature. NBT xBT materials in the compositional range between 0.05 ≤ x ≤ 0.11have been shown to contain nanodomains embedded in a non-polar cubic matrix. The fluctuations of these nanodomains give rise to the relaxor behavior which in some cases is referred to as "relaxor antiferroelectric". In contrast to ferroelectric materials, in relaxor ferroelectrics thermal fluctuations can cause the poled nanodomains to relax to an unpoled state. It is necessary to understand local structure effects on the piezoelectric response at the grain level in order to develop materials with improved performance. Using Piezoresponse Force Microscopy (PFM), this study examines the domain motion within individual grains and domain evolution over time under locally applied electric fields as well as single-point hysteresis loop measurements in thin film NBT and NBT-xBT. These experiments provide an understanding of the domain behavior that cannot be acquired through bulk, macroscopic measurements. Thin films are fabricated using hydrothermal deposition and pulsed laser deposition. The films are highly oriented and exhibit relaxor behavior at room temperature. Date: Tuesday, April 9, 2013 Time: 9:00 A.M. Place: HAMP 1113 Thank you, Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

1 0

Fwd: PPDA Coffee Hour Friday 12:30PM
by Donna Bystrom 05 Apr '13

05 Apr '13

1 0

FW: SEMINAR NOTICE: S. Lawrence, PhD Prelim I, Fri., 4/12/13, 11:30 am, ARMS 1028
by Stacey, Lisa A 04 Apr '13

04 Apr '13

Please see seminar notice below: MATERIALS SCIENCE AND ENGINEERING SEMINAR Mechanisms of Hydrogen Degradation in Metals By: Samantha Lawrence Ph.D. Prelim Exam – Part I Advisor: Prof. D. F. Bahr ABSTRACT Hydrogen is an important energy carrier; however, there are substantial barriers to effective hydrogen transport and storage. Degradation of metallic systems exposed to hydrogen (especially those used in pressure vessels, tanks, and pipelines of various energy industries) leading to unexpected catastrophic failures is particularly disturbing. Hydrogen is linked to a decrease in ductility, fracture strength, and fracture toughness in many metals (the phenomenon of hydrogen embrittlement). Three broadly grouped degradation mechanisms have been identified: (1) hydride formation, where brittle hydride precipitates ease fracture by providing low energy crack paths; (2) hydrogen-enhanced localized plasticity (HELP), where localized deformation increases in the presence of hydrogen due to a decrease in barriers to dislocation motion; and (3) hydrogen-enhanced decohesion (HEDE), where hydrogen reduces interfacial atomic bond strengths resulting in a sharp transition between ductile and brittle fracture. Hydrogen diffusion and subsequent capture at microstructural inhomogeneities, or traps, is required to establish a critical H-concentration prior to failure. Realizing that a “one‑size‑fits‑all” mechanism explaining observations of hydrogen embrittlement is unlikely, proposed degradation mechanisms are presented and future work geared toward understanding the interrelationships between the mechanisms is proposed. Date: Friday, April 12, 2013 Time: 11:30 A.M. Place: ARMS 1028 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

1 0

FW: SEMINAR NOTICE, K. Fezi, MS Final Exam, Thur. 4/11, 1:30 pm, ARMS 1103
by Stacey, Lisa A 04 Apr '13

04 Apr '13

Please see seminar notice below: MATERIALS SCIENCE AND ENGINEERING SEMINAR Modeling of Transport Phenomena During Electroslag Remelting of Alloy 625 By: Kyle S. Fezi Master of Science Final Examination Advisor: Prof. M. J. M. Krane ABSTRACT A numerical model is used to examine the transport phenomena during Electroslag Remelting (ESR), primarily the phenomenon of macrosegregation. Another model has been developed to study morphological effects on macrosegregation during the ESR process, including grain growth kinetics and solid grain movement. Both models are built on an existing model that is capable of solving mass, momentum, species, and energy conservation equations during multicomponent solidification. ESR is a secondary melting process used to enhance the metallurgical structure and refine the chemistry of an ingot. ESR consists of passing an alternating current through a consumable electrode immersed in an electrically resistive slag that generates enough heat to melt the electrode. There are limitations for ESR due to an increase in segregation levels with ingot diameter. In order to produce larger ingots than current practice, several constant current ESR runs are simulated to explain possible ways to minimize the segregation levels. Low currents are found to decrease the segregation level as well as shifting the initial composition to decrease the solutal buoyancy force. The columnar-to-equiaxed transition model is used to examine the effect of having free-floating equiaxed grains in the center of a casting. The CET is shifted by changing the thermal boundary conditions, the free-floating equiaxed particle diameter, and the possible number of heterogeneous nucleation sites. Comparisons are drawn between the static castings of the CET model and the ESR ingots. Date: Thursday, April 11, 2013 Time: 1:30 P.M. Place: ARMS 1103 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

1 0

Fwd: PPDA Annual Dinner
by Donna Bystrom 03 Apr '13

03 Apr '13

1 0

FW: MSE Peter Winchell Seminar Notice: Christoph Beckermann, UI, Fri., 4/12/13, 3:30 pm, ARMS 1010
by Stacey, Lisa A 03 Apr '13

03 Apr '13

Please see the attached announcement for our Peter G. Winchell Lecture Series Keynote Speaker, Prof. Christoph Beckermann, next Friday, April 12th. Thank you, Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

1 0

FW: REMINDER: Seminar Notice - C. Fancher, PhD Final Exam, Thur. 4/4/13, 9:30 am, HAMP 1113
by Stacey, Lisa A 03 Apr '13

03 Apr '13

Please see seminar reminder below (note location outside of ARMS): MATERIALS SCIENCE AND ENGINEERING SEMINAR Texture and Anisotropy in the Bismuth Sodium Titanate System By: Christopher M. Fancher Ph.D. Final Examination Co-Advisors: Prof. K. J. Bowman and Prof. J. E. Blendell ABSTRACT Bi0.5Na0.5TiO3 has received interest as a potential replacement for lead containing ferroelectrics. However, the piezoelectric response of pure Bi0.5Na0.5TiO3 does not compare to the strong piezoelectric response of lead based piezoelectrics. To increase the piezoelectric response, Bi0.5Na0.5TiO3 has been alloyed with BaTiO3 and K0.5Na0.5NbO3. Another route to enhance the response is to take advantage of the anisotropic properties by inducing a preferred crystallographic orientation. Both routes were used to investigate the effect a crystallographic texture has on the strain response of Bi0.5Na0.5TiO3-based ceramics. A crystallographic texture was induced by templated grain growth of pure phase Bi0.5Na0.5TiO3 templates using the tape casting method to orient template particles relative to the tape cast normal. Sintered Bi0.5Na0.5TiO3 based materials developed a strong (00l)pc fiber texture relative to the tape cast normal, with no preferential alignment relative to the tape cast plane. Textured Bi0.5Na0.5TiO3-(5)BaTiO3 showed a piezoelectric response of 245 pC/N, a better than 50% enhancement from the 150 pC/N response of randomly oriented samples. The Bi0.5Na0.5TiO3-(x)BaTiO3-(y)K0.5Na0.5NbO3 (x,y) system has been shown to undergo electric-field-induced phase transformation from a pseudocubic to polar phase. For (7,2) a strong 8.67 multiples of a random distribution (MRD) crystallographic texture increased the macroscopic strain response by 50%. Applying the electric field perpendicular to the fiber texture axis reduces the macroscopic strain response of textured (7,2) by 17%. The affect field direction has on the electric-field-induced phase transformations of textured (7,2) was investigated using in situ electric field dependent diffraction. In situ diffraction data showed the high strain response of textured (7,2) can be attributed to a reversible pseudocubic to tetragonal transformation. The field-induced tetragonal phase nucleates preferentially with a strong c-axis alignment in the electric field direction, ferroelastic domain texture. In situ diffraction data suggests the origin of the reduction in strain associated with a field applied perpendicular to the fiber texture axis is the result of a shorter induced lattice spacing and lower domain texture. Date: Thursday, April 4, 2013 Time: 9:30 A.M. Place: HAMP 1113 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

1 0

SEMINAR NOTICE: M. Dubelman-PhD Final, Tue. 4/9/13, 9:00 am, HAMP 1113
by Stacey, Lisa A 01 Apr '13

01 Apr '13

Please see seminar notice below: MATERIALS SCIENCE AND ENGINEERING SEMINAR Domain Evolution in Lead-Free Thin Film Piezoelectric Ceramics By: Meredith E. Dubelman Ph.D. Final Examination Advisor: Prof. J. Blendell ABSTRACT Due to environmental and health concerns lead-free piezoelectric systems are currently being evaluated for use as replacements for lead-based ceramics. Sodium Bismuth Titanate, Na0.5Bi0.5TiO3 (NBT) - based materials offer possible alternatives. NBT is a perovskite-type, ABO3, compound and is ferroelectric at room temperature. It has a relatively high Curie temperature, a large remnant polarization, and a high coercive field at room temperature. NBT can be modified by additives, such as BaTiO3 (BT), to improve its properties further. NBT-xBT was originally reported to have a morphotropic phase boundary which lies at x = 0.06. The structure transforms from rhombohedral for x < 0.06 to tetragonal for x > 0.06. However, recent studies have shown that for some compositions NBT-xBT develop a relaxor phase at room temperature. NBT xBT materials in the compositional range between 0.05 ≤ x ≤ 0.11have been shown to contain nanodomains embedded in a non-polar cubic matrix. The fluctuations of these nanodomains give rise to the relaxor behavior which in some cases is referred to as "relaxor antiferroelectric". In contrast to ferroelectric materials, in relaxor ferroelectrics thermal fluctuations can cause the poled nanodomains to relax to an unpoled state. It is necessary to understand local structure effects on the piezoelectric response at the grain level in order to develop materials with improved performance. Using Piezoresponse Force Microscopy (PFM), this study examines the domain motion within individual grains and domain evolution over time under locally applied electric fields as well as single-point hysteresis loop measurements in thin film NBT and NBT-xBT. These experiments provide an understanding of the domain behavior that cannot be acquired through bulk, macroscopic measurements. Thin films are fabricated using hydrothermal deposition and pulsed laser deposition. The films are highly oriented and exhibit relaxor behavior at room temperature. Date: Tuesday, April 9, 2013 Time: 9:00 A.M. Place: HAMP 1113 Thank you, Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

1 0

SEMINAR REMINDER: Ozgur Keles PhD Final Exam, Tue. 4/2/13, 8:30 am, ARMS 1028
by Stacey, Lisa A 01 Apr '13

01 Apr '13

Please see seminar info below for tomorrow: MATERIALS SCIENCE AND ENGINEERING SEMINAR Modeling Failure of Brittle Porous Ceramics By: Özgür Keleş Ph.D. Final Examination Co-Advisors: Prof. R. E. Garcia & Prof. K. J. Bowman ABSTRACT Brittle porous materials (BPMs) are used for battery, fuel cell, catalyst, membrane, filter, bone graft, and pharmacy applications due to the multi-functionality of their underlying porosity. However, in spite of its technological benefits the effects of porosity on BPM fracture strength and Weibull statistics are not fully understood--limiting a wider use. In this context, a two-dimensional finite element (FE) simulation-based approach was developed to assess the pore--pore interactions and their impact on fracture statistics of isotropic microstructures. The classical fracture mechanics approach was combined with FE simulations that account for the interactions to predict the decrease in the fracture stress with increasing porosity. Simulations show that even the microstructures with the same porosity level and size of pores differ substantially in fracture strength. The maximum reliability of BPMs was shown to be limited by the underlying pore--pore interactions. BPM fracture strength decreases at a faster rate under biaxial loading than under uniaxial loading. Three different types of deviation from classic Weibull behavior are identified: P-type corresponding to a positive lower tail deviation, N-type corresponding to a negative lower tail deviation, and S-type corresponding to both positive upper and lower tail deviations. Pore-pore interactions result in either P-type or N-type deviation in the limit of low porosity. Whereas, S-type behavior occurs when clusters of low and high fracture strengths coexist in a fracture data. Date: Tuesday, April 2, 2013 Time: 8:30 A.M. Place: ARMS 1028 Thank you, Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100

1 0