2015 Symposium Abstracts - Materials Science

MSE-01 Swift Heavy Ion Irradiation Damage In Ti-6Al-4V And Ti-6Al-4V-1B: Study Of The Microstructure And Mechanical Properties.

Authors: Aida Amroussia; Carl J. Boehlert;Florent Durantel; Clara Grygiel; Wolfgang Mittig; Isabelle Monet; Frederique Pellemoine

Abstract: Due to their excellent mechanical properties, corrosion resistance, fatigue strength, low density and low activation under irradiation, titanium (Ti) alloys are currently being considered for use as a structural material for the beam dump shell for the Facility for Rare Isotope Beams (FRIB): A new generation accelerator with high power heavy ion beams. The capability of the FRIB to operate at full beam power depends on the beam dump being able to absorb up to a 325 kW beam power (with primary Beam from O to U). Ti-6Al-4V (grade 5) is the preferred candidate for this beam dump shell material. A significant increase of beam dump lifetime with respect to fatigue due to thermal cycling can be expected for the rotating beam dump if Ti-6Al-4V with an addition of 1% boron (Ti-6Al-4V-1B) is used [1]. Two sets of samples of both Ti-6Al-4V and Ti-6Al-4V-1B were irradiated at the IRRSUD beam line at the GANIL CIMAP, Caen France with swift heavy ion beams respectively 36Ar (36MeV, Se =7.5keV/nm) and 131Xe (92MeV, Se =19.7 keV/nm).  The samples were polished and etched before irradiation and selected areas on the surfaces of the samples were characterized before and after irradiation using Scanning Electron Microscopy and Electron Backscatter Diffraction. In addition, Vickers hardness and nano-indentation measurements were also used to probe the change in hardness and elastic modulus as a function of the depth. The poster will describe irradiation setups and the post irradiation techniques used to characterize the material. The results indicate a low-radiation damage sensitivity in both materials. [1] W. Chen, C. J. Boehlert (2009). Materials Transactions,, Vol. 50, No. 7 pp. 1690 to 1703.

This work was supported in part by U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan and Michigan State University

 

MSE-02 Contraction Twinning Dominated Tensile Deformation And Subsequent Fracture In Extruded Mg-1Mn (wt%) At Ambient Temperature

Authors: Ajith Chakkedath; C.J. Boehlert; J. Bohlen; S. Yi; D. Letzig

Abstract: Due to superior strength-to-weight ratio, Mg alloys are attractive for applications where weight savings are critical. However, limited cold formability of wrought Mg alloys severely restricts its widespread usage. This is partly attributed to the insufficient number of independent deformation systems to accommodate uniform elongation according to von Mises criterion. However, additional mechanisms might play a role in limited elongation-to-failure. In order improve the cold formability of Mg alloys it is critical to understand the mechanisms that limit the elongation-to-failure. In this study, we are reporting a contraction twinning based mechanism responsible for failure at lower strains under tensile loading in extruded Mg-1Mn (wt%). The alloy studied is of interest for a variety of applications including biomedical applications. Contraction twinning dominated the tensile deformation in extruded Mg-1Mn (wt%) at 50°C. The contractions twins evolved in to {10-11}-{10-12} double twins which accounted for the formation of shear bands in the twinned volume. The formation of shear bands was expected to be due to the enhanced activity of basal <a> slip in the twinned region. With an increase in strain, cracks were developed along the shear bands which eventually resulted in shear failure. The activity of contraction twinning decreased with increase in temperature, and at 250°C no contraction twinning was observed. This was expected to be due to the lower CRSS value for pyramidal <c+a> slip compared to contraction twinning at elevated temperatures. The deformation at 150°C and 250°C was dominated by slip mechanisms. Thus, the improved elongation-to-failure at elevated temperatures was attributed to the limited activity of contraction twinning.

This work was supported in part by NSF Division of Material Research “Materials World Network” (Grant No. DMR1107117)

 

MSE-03 Electrospun Carbon Nanofiber Supports For Bioelectrodes

Authors: Duyen Do; Cenk Gumeci; Scott Calabrese Barton

Abstract: High surface-area electrospun carbon nanofiber (CNF) supports for bioelectrodes are introduced to enhance enzyme utilization. This study employed Glucose Oxidase (GOx) in a redox hydrogel system, which mediates electron transfer via Osmium (Os2+/Os+) centers, to create a glucose bioelectrode. The strategy was to enhance the transport of electrons via the redox mediator by reducing the average hydrogel thickness at fixed hydrogel volume. The tunable electrospun carbon fiber reduces hydrogel film thickness via uniform distribution on small fibers of high surface area. Glucose oxidizing current density at electrodes made from electrospun carbon nanofiber and several commercial counterparts suggest a possibility for low-cost fibers, in a diameter range below 100 nm, that enable high current density (~8.5 mA/cm2) comparable to multiwalled carbon nanotubes (MWCNTs). To adjust electrospun CNF size, various concentrations of Polyacrylonitrile (PAN)/ Dimethylformamide (DMF) precursor solution (7 wt% to 14 wt%) were spun in a high voltage field prior to oxidation, stabilization and carbonization in Argon environment at two temperatures, 850°C and 1100°C. Graphitization of CNFs increased with the increasing heat treatment temperature, demonstrated by Raman spectroscopy, leading to increased conductivity. CNFs based on 7 wt% PAN/DMF carbonized at 1100°C had a diameter of 150 nm (a decrease from 250 nm uncarbonized PAN fibers), and showed good performance in electrochemical characterization compared to MWCNT electrodes.

 

MSE-04 Investigation Of Strain Transfer Across Grain Boundaries In Commercially Pure Tantalum

Authors: Bret Dunlap; Philip Eisenlohr; Claudio Zambaldi; David Mercier; Yang Su; Thomas Bieler; Martin Crimp

Abstract: In order to investigate heterogeneous deformation across grain boundaries in commercially pure tantalum, nanoindentation was carried out near and far from boundaries to induce bi-crystal and single-crystal deformation. Electron backscatter diffraction orientation mapping was used to measure grain orientations and grain boundary misorientations. Grain boundary inclinations were determined using focused ion beam cross-sections. Indent pile-up topographies were characterized through atomic force microscopy. Using a topography subtraction procedure, single and bi-crystal indents were compared and used to examine grain boundary effect on strain transfer. Crystal plasticity finite element simulations of bi-crystal indents were performed. To ensure efficient generation of the finite element models, a graphical user interface was used to input the experimental conditions into the simulations. Using the same subtraction procedure, differences between the simulations and experiments were quantified. Dislocation activity around the indents was assessed using electron channeling contrast imaging and compared to activated systems identified by the simulation.

This work was supported in part by Sandia National Lab, NSF, DFG, and DOE-BES

 

MSE-05 Carbonate-Doped P-Type Mg2Si0.4Sn0.6 Materials

Authors: Peng Gao; Tim Hogan

Abstract: The Mg2(Si,Sn) materials are promising candidate materials for thermoelectric power generation applications in the 500-800K temperature range. There have been extensive studies on the n-type Mg2(Si,Sn) materials while the p-type compounds were less extensively investigated. A carbonate-doping approach was used in our research to improve the ZT of the p-type Mg2Si0.4Sn0.6 materials. It was found that the alkali metal carbonate had the similar doping effect on the Mg2Si0.4Sn0.6, compared with pure alkali metal. Lithium carbonate (Li2CO3) was found to be the most effective dopant among all the carbonates. A state of art ZT~0.6 for p-type Mg2(Si,Sn) materials was found in the Li2CO3-doped Mg2Li0.05Si0.4Sn0.6 materials.

This work was supported in part by DOE--EFRC

 

MSE-06 Study Of Slip In High Purity Single Crystal Nb For Accelerator Cavities

Authors: Di Kang; Derek Baars; Thomas Bieler; Chris Compton

Abstract: High purity Nb has been used to build accelerator cavities over the past couple decades. The study of slip and dislocations using single crystal Nb is an initial step towards understanding the metallurgical state evolution of large grain Nb during cavity fabrication. Two groups of specimens with different orientations were extracted. The first group was deformed monotonically to 40% engineering strain. Analyses suggest that slip on {112} planes controlled the hardening behavior. The second group was heat treated at 800ºC for two hours, and then deformed incrementally to 40% engineering strain. Results indicate that {110} slip was favored instead. Activated slip systems were verified using the crystal rotations with deformation. The variation in initial specimen states poses a challenge to interpreting and predicting the deformation behavior of Nb.

This work was supported in part by U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638

 

MSE-07 Molecular Dynamics Studies Of Diffusion Dynamics During Lithiation Of Si Electrode: Increasing Si Vacancies Can Improve The Lithiation Rate

Authors: Kwang Jin Kim; Yue Qi

Abstract: The study of diffusion properties upon lithiation is important and challenging topic since the stress generation and rate performance of electrodes for lithium-ion batteries are affected by diffusion of active materials. This issue becomes more intriguing for Si anodes, whose ultrahigh capacity is accompanied by 300% volume expansion and structural changes occurring upon lithiation which results in mechanical fracture, capacity loss, and limited cycle life. In order to study diffusion kinetics of both Si and Li during lithiation, we performed MD simulations using reactive force field. To study the characteristic diffusion patterns among different Si surface orientations, we computed local concentrations corresponding to lithiation direction. We find out that Li diffusion patterns are affected by the location of (111) planes, which Li atoms proceed by layer-by-layer peeling off of {111} atomic facets. We also studied the relationship between concentrations and diffusion coefficients of Li by correlating the local MSD and RMSD with corresponding local concentrations. Our results clearly demonstrate diffusion of Li is concentration dependent, where higher lithium concentration results in faster diffusion. To further understand the control factor of concentration dependent diffusion, we introduced 10% random vacancy in Si and Li and studied the movement of the reaction front. We find that Si vacancy accelerates the movement of the reaction front which clearly indicates that movement of Si is the rate-limiting factor. These findings provide great insight into understanding lithiation process and increasing the lithiation rate, which contribute to enhance the rate performance of Si anode.

 

MSE-08 Atomistic Simulation Of Phase Transformation In Al Dope Li7La3Zr2O12

Authors: Matthew Klenk; Wei Lai

Abstract: The fast ion conducting lithium garnet oxide Li7La3Zr2O¬12 (LLZO) has been studied as a suitable solid electrolyte to replace conventional separators in lithium ion batters due to its stability to lithium metal and high ionic conductivity which approaches 10-3 Scm-1. However, pure LLZO exhibits two phases: a high temperature cubic and low temperature tetragonal phase. Only a stabilized cubic phase is highly conductive at ambient temperature and various cation doping strategies have been employed to stabilize the cubic phase. This study investigates the role of aluminum in modifying the local structure and dynamics of lithium in AlxLi7-3xLa3Zr2O12 (Al-LLZO) using energy minimization (GULP1) and molecular dynamic simulations (DLPOLY_Classic2). Various studies have reported that aluminum stabilizes cubic LLZO at lower temperatures, but the mechanism through which this is achieved is still debated. Previous work by our research group investigated the thermally induced phase transformation of LLZO.3 With sufficient thermal energy lithium will overcome the configurational entropy of LLZO resulting in disorder about lithium sites which in turn drives the phase transformation from tetragonal to cubic. Energy minimization simulations show that the doping of aluminum into LLZO results in aluminum replacing lithium at tetrahedral sites. The electrostatic repulsion of aluminum forces neighboring lithium to previously unoccupied 16e tetrahedral sites inducing lithium disorder similar to the thermally induced disorder of pure LLZO. References J.D. Gale; A.L. Rohl. Mol. Simul. 2003, 29, 291-341.  Smith, W.; Forester, T. R. J. Mol. Graphics 1996, 14, 136−141. Klenk; Lai. Phys. Chem. Chem. Phys.,2015, DOI: 10.1039/c4cp05690f.

This work was supported in part by Ceramics Program of National Science Foundation (DMR-1206356)

 

MSE-09 Comparing The Predictions Of Non-Schmid And Schmid Crystal Plasticity Models For BCC Materials

Authors: Aboozar Mapar; Thomas Bieler; Farhang Pourboghrat

Abstract: Classical crystal plasticity does not accurately predict the deformation behavior of BCC single crystals. One reason for this short coming is that the deformation of BCC single crystals does not follow the Schmid law. In fact, stresses non-parallel to slip direction or non-planar with dislocation line affect the critical stress necessary to activate the dislocation motion. This is usually modeled through non-Schmid crystal plasticity. In this study a Schmid and a non-Schmid crystal plasticity are developed and used to predict the deformation behavior of single crystal Niobium (BCC). The predictions of these two models are then compared.

 

MSE-10 Tensile, Creep, And Fatigue Analysis Of Friction Stir Welded Al 2139-T8 Alloy

Authors: Uchechi Okeke; Tomoko Sano; Jian Yu; Chian-Fong Yen; Carl Boehlert

Abstract: Aluminum alloys are commonly used for structural applications due to their high strength and low weight. Welding techniques are often applied to join two or more aluminum alloy plates together. The welding process introduces heat, plastic deformation, and chemical variation into the weld joints and modifies the microstructure, strength, and elongation-to-failure of the welded region. The Al 2xxx alloy series is difficult to weld using conventional methods, therefore friction stir welding is being studied. Samples studied were extracted from two plates of Al 2139-T8 alloys friction stir welded together. Electron backscattered diffraction was performed on the cross section of the weld. Hardness testing was performed on the base metal (BM) and the friction stir welded (FSW) regions. Tensile, fatigue, and creep tests were performed on the BM and FSW regions. The results of the room temperature fatigue tests at 100, 150, 200, and 250 MPa indicated no significant differences in performance between the BM and the FSW regions. The creep test results at 250C and 300C at 25MPa and 50MPa reveal that the FSW region has significantly poorer creep resistance than the BM samples. Backscattered electron (BSE) images were taken of the microstructures of failed samples of both tests to try to understand the different fracture behaviors of the materials.

This work was supported in part by National Science Foundation Division of Material Research (Grant No. DMR1107117); material was provided by the U.S. Army Research Lab

 

MSE-11 Characterization Of Twinning Behavior And Corresponding Crystal Plasticity-Based Modeling In Commercial Purity Titanium

Authors: H. J. Phukan; C. Zhang; P. Eisenlohr; L. Wang; J.S. Park; P. Kenesei; T. R. Bieler; D. Mercier; M. A. Crimp

Abstract: A clearer understanding of the micromechanical conditions favoring the nucleation and growth of extension (T1) twins in alpha titanium is sought using far field 3D X-ray diffraction from a synchrotron source at the APS. In-situ characterization of eleven 100 micron thick layers along the gage length of a highly textured tensile sample were recorded. T1 twin–parent grain pairs were identified using criteria for c and a axis misorientation and spatial proximity. The possibility of twin nucleation by slip transfer, or twin-induced shear transfer across a grain boundary was assessed using slip transfer parameters. From the grain center-of-mass positions, a 3D representation of the measured microstructure was constructed using Voronoi tessellation. The experimental average grain stress tensor values were compared to results from a spectral method crystal plasticity simulation, and computed local stress states at twin nucleation sites were assessed. Supported by NSF Materials World Network grant NSF-DMR-1108211.

This work was supported in part by Materials World Network, National Science Foundation, use of APS supported by the Office of Basic Energy Sciences, Department of Energy

 

MSE-12 Engineering Poly(lactide) For Blown Film Applications

Authors: Jeff Schneider; Xiangke Shi; Ramani Narayan

Abstract: Epoxy Functionalized Poly(lactide) (EF-PLA) was synthesized by reacting PLA with a multifunctional epoxy polymer (MEP) using reactive extrusion (REX) processing. These polymers can function as a rheology modifier for PLA and a compatibilizer for other biopolyesters in blown film and foam applications. Model compound studies show that the epoxy functional group on the MEP reacts selectively with the carboxylic acid chain-ends of PLA at processing temperatures below 200C. An EF-PLA containing up to 10% MEP was prepared without gel formation and reactively extruded with neat PLA to obtain three different product formulations containing MEP (0.25%, 0.5%, and 1.0%). These products showed significantly enhanced rheological properties compared to what has been reported by other groups and is currently used in the PLA blown film industry, the blending of MEP with PLA in a single step. These benefits are a result of how the MEP gets distributed in the material, and can lead to improved properties even at lower MEP concentrations. Our new materials showed significant strain hardening rheological behavior demonstrating that they can be readily blown into films and foams. A statistical simulation was developed to provide a fundamental understanding of the reaction as well as provide information on the molecular weight characteristics and reactivity of the EF-PLA. The EF-PLA molecule shows good potential for use as a rheology modifier and compatibilizer. It has been successfully used in the production of biobased films at the commercial scale.

This work was supported in part by National Science Foundation (NSF) for funding this project under Grant #1127552

 

MSE-13 Preparation Of Poly (Lactic Acid)/Polystyrene Bioblend Hollow Microparticles Embedded With Nanoparticles Via A One-Step Emulsion-Diffusion Method

Authors: Anna Song; Shaowen Ji; Chris Tawfik; Ilsoon Lee

Abstract: Poly (lactic acid) (PLA) is a highly potential drug delivery carrier because of its biodegradation and biocompatibility. However, the brittleness and high cost of PLA limit its application. PLA combined with polystyrene (PS) has been considered as a potential bioblend for biomedical applications. In this work, PLA and PS have been dissolved in ethyl acetate under heating, which is a good solvent for PLA but a non-good solvent for PS. This PLA/PS blending solution has then been mixed with a 1:1(v/v) water/glycerol system to form an oil-in-water emulsion, which is followed by the diffusion process to obtain the spherical particles. From the SEM result, hollow microparticles embedded with nanoparticles can be clearly observed. Electron energy loss spectroscopy (EELS) will be employed to define the composition of the dispersive nanoparticles and the continuous phase of the microparticles, respectively. This type of microparticles can be used to design a “two-stage” release system for drug delivery due to the two separated polymer phases and will be tested in the future work.

This work was supported in part by SPG funding

 

MSE-14 Quantifying Deformation Processes Near Grain Boundaries In Alpha Titanium Using Nanoindentation And Crystal Plasticity Modeling

Authors: Yang Su; Claudio Zambaldi; David Mercier; Philip Eisenlohr; Thomas Bieler; Martin Crimp

Abstract: To understand the roles that different grain boundaries play in plastic deformation of commercially pure titanium, instrumented sphero-conical nanoindentations were placed at preselected grain boundaries where corresponding grain orientations had been mapped by electron backscatter diffraction. The topographies of the nanoindents were measured using atomic force microscopy. The effects of grain boundary misorientation and boundary inclination (determined by focused ion beam sections) on indentation pile-ups were categorized by slip transmission parameters. Corresponding bi-crystal indentations simulations were carried out using crystal plasticity finite element (CPFE) models to better understand the details of the mechanical response of the grain boundaries to different slip systems. The constitutive parameters for these CPFE simulations were adjusted through an optimization process that matches simulated to experimental topographies of indents collected in grain interiors [Zambaldi et al. J. Mater. Res. 27, 356–367 (2012)]. The ability of the current CPFE method to predict bi-crystal grain boundary response to plastic deformation has been evaluated for different grain boundaries with the aim of implementing grain boundary behavior in to the CPFE polycrystal simulations.

This work was supported in part by NSF Materials World Network Grant DMR-1108211 and corresponding DFG grant ZA523/3-1

 

MSE-15 Reduction Of The Thermal Conductivity Of PtSb2 For Low Temperature Thermoelectric Use

Authors: Spencer Waldrop; Donald Morelli

Abstract: Effectively cooling space based electrical systems is inherently difficult due to the sensitivity of the machinery, the challenges of transportation into space, and the extremely low temperatures that must be achieved. Current high efficiency thermoelectric materials are designed to operate at above room temperature and are ill-suited for the task of cooling to temperatures of 150 K or below. Previous study has shown that PtSb2 has potential to be a material useful for this purpose. One of the main inhibitors to the use of PtSb2 is the inherently high thermal conductivity that it exhibits. Utilizing the substitution of Pd for Pt a reduction in the thermal conductivity of the material can be achieved which may increase its efficiency substantially. Samples were made with a composition of Pt1-xPdxSb2 where x= 0.05 to 0.50. The reduction of thermal conductivity via this method proved successful with a reduction from 35 Wm-1K-1 to less than 6 Wm-1K-1 at low temperatures. A moderate change in the electrical resistivity and Seebeck coefficients resulted in improved efficiency in some samples at temperatures greater than 180 K. These results inspire further research into the substitution of Pd for Pt to discover at what composition the thermal conductivity is minimized and the efficiency is maximized.

This work was supported in part by Air Force Office of Scientific Research under the Multi-University Research initiative (MURI), “Cryogenic Peltier Cooling,” Contract No. FA9550-10-1-0533

 

MSE-16 Analysis Of Slip Activity And Deformation Modes In Tension Tests Of Cast Mg-10Gd-3Y-0.5Zr (wt.%) At Elevated Temperatures Using In-Situ SEM Experiments

Authors: Huan Wang; Carl Boehlert; Qudong Wang

Abstract: The tension behavior of a cast Mg-10Gd-3Y-0.5Zr (wt.%, GW103) alloy at elevated temperatures was investigated using in-situ observation inside a scanning electron microscope (SEM). The tests were performed at 473 K, 523 K, 573 K and 598 K. Both the ultimate tensile strength and the yield strength of the studied alloy decreased with increasing temperature. The active slip systems were identified for each test using an EBSD-based slip trace analysis, and the global stress state Schmid factor distribution for the activated systems was summarized. The results showed that for all of the tests, basal slip was the most likely system to be activated, and non-basal slip was activated to some extent depending on the temperature. No twinning was observed. Non-basal slip consisted of ~35% of the deformation modes at low temperatures (473 K and 523 K), while basal slip consisted of between 88% to 93% of the deformation modes at high temperatures (573 K and 598 K). Pyramidal <c+a> slip was more easily activated compared to prismatic <a> slip with increasing temperature. Slip-transfer in neighboring grains was prevalently observed for the low-temperature tensile tests. Intergranular cracking occurred at grain boundaries nearly perpendicular to the loading axis during tension. Grain boundary ledges were prevalently observed for the tensile tests at high temperatures (573 K and 598 K), which suggests that besides dislocation slip, grain boundary sliding contributed to the deformation.

 

MSE-17 Dislocation-Magnetic Field Interactions In Nb Used For Superconducting Particle Accelerator Cavities

Authors: Mingmin Wang; Di Kang; Zuhawn Sung; Peter J. Lee; Anatolii A Polyanskii; Christopher C Compton; Thomas R. Bieler

Abstract: Pinning of magnetic flux usually occurs at local surface defects within Nb superconducting radio frequency cavities during operation at 2-4K. This leads to power dissipation (hot spots) that degrade the cavity performance. Thus the relationship between dislocations produced from controlled mechanical deformation and magnetic flux pinning is investigated. Laue X-ray characterization of ingot slices and EBSD-OIM crystallographic analysis are used to identify crystallographic orientations and orientation gradients of single crystal Nb samples deformed in tension. Cryogenic magneto-optical imaging is used to characterize the behavior of magnetic flux on the deformed Nb. By selecting grain orientations to favor specific dislocation slip systems in tensile testing, dislocations are generated on primary and secondary slip systems. TEM is used to identify defects and their distributions close to the Nb surface. Their effect on flux pinning in single crystal Nb is assessed, and compared to deformation expected in typical cavity forming processes.

 

MSE-18 The Efects Of Sn Substitution On The Thermoelectric And Phase Transition Properties Of Ge4SbTe5

Authors: Jared B. Williams; Spencer Mather; Donald T. Morelli

Abstract: The world’s energy demands have continued to increase over the past century, and the method of producing energy is primarily through the burning of hydrocarbon based fuels such as gas, coal, and oil. To avoid the use of nonrenewable energy sources research is being dedicated to find alternative and renewable sources of energy. Among the many new forms of energy harvesting technologies are thermoelectric materials. Thermoelectric materials possess the ability to convert wasted thermal energy into electrical energy through solid-state processes. The efficiency of this process is constrained by the Carnot efficiency and ZT, the dimensionless figure-of-merit, which is dependent on the intrinsic electrical and thermal properties of the thermoelectric material at hand. Though the materials have the potential to increase the efficiency of modern energy sources, the materials still have many obstacles to overcome: such as price, efficiency, and toxicity of materials used. It was recently shown that Ge-Sb-Te based phase change materials exhibit high thermoelectric efficiencies above 673 K. The following work has studied Ge4SbTe5 and the effects of substituting Sn atoms on the germanium site. The substitution of Sn for Ge scatters heat-carrying phonons and thereby reduces the thermal conductivity, which is beneficial for thermoelectric conversion. The substitution of Sn also alters the phase transition properties of Ge4SbTe5, which undergoes a transition from the cubic rocksalt phase to the rhombohedral phase at 473 K.

This work was supported in part by Revolutionary Materials for Solid State Energy Conversion, and Energy Frontier Research Center sponsored by the Department of Energy

 

MSE-19 Analysis Of The Subsurface Slip Activity During Plastic Deformation Using Crystal Plasticity Finite Element Method With Realistic 3D Microstructure

Authors: Chen Zhang; Philip Eisenlohr; Thomas R. Bieler; Martin A. Crimp;  Carl J. Boehlert;

Abstract: Computational models with a microstructure that is representative of the sample are commonly used to investigate heterogeneous slip, but such models are not correlated with experiments. To assess how well a model can simulate heterogeneous deformation, a simulation was made based on measured local deformation of a subset of about 30 surface and subsurface grains of a Ti-5Al-2.5Sn polycrystal deformed under uniaxial tension using a crystal plasticity finite element (CPFE) model. The 3D microstructure model was built using Electron Backscatter Diffraction (EBSD) and Differential Aperture X-Ray Microscopy (DAXM) data. Schmid analysis using the local stress tensor and generalized m’ slip transfer analysis using local accumulative shear extracted from the simulation were correlated with experimental observations to gain better understanding of the effect of subsurface slip activity on the observed surface deformation history of the alloy. DAXM was done at beamline 34-ID-E, Advanced Photon Source. Supported by DOE/BES grant DE-FG02-09ER46637.

This work was supported in part by DOE/BES, grant number: DE-FG02-09ER46637

 

MSE-20 Microstructure Evolution And Stress-Strain Analysis Of Wafer Level Chip Scale Package (WLCSP) Solder Joints With Different Thermal Cycles

Authors: Quan Zhou; Bite Zhou; Thomas Bieler; Tae-Kyu Lee

Abstract: Wafer-level chip-scale package samples with pre-cross-sectioned edge rows were thermally cycled to study microstructure evolution and damage development. Electron backscattered diffraction (EBSD) and high-energy x-ray diffraction were used to obtain Sn grain orientations and the average coefficient of thermal expansion normal to the board in every joint of the package for samples in the as-fabricated and thermally cycled conditions. The results indicated a near-random distribution of joint orientation. Optical, scanning electron microscopy, and EBSD methods were used to characterize microstructure changes in pre-cross-sectioned samples due to thermal cycling. Slip trace analysis and Orientation Imaging Microscopy (OIM) show that slip systems with high Schmid factors (estimated global shear stress based on the package neutral point) are responsible for the observed microstructure evolution during thermal cycling, which provides information about slip systems that are more easily activated. Two joints were analyzed in detail to evaluate slip activity at different stages of their thermal history. The first case showed that a solidification twin grain boundary can influence damage development and the path of crack propagation. The second case showed a new grain orientation developing due to gradual lattice rotation about the Sn [110] axis by a continuous recrystallization mechanism. This rotation was correlated with the operation of slip system {110)<001]. As the local stresses are not known experimentally, this analysis provides observations that can be compared with a crystal plasticity model simulation.

This work was supported in part by NSF-GOALI Contract 1006656 and Cisco Systems Inc., San Jose, CA. Use of Advanced Photon Source was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.