Data-driven approach for synchrotron X-ray Laue microdiffraction scan analysis

We propose a novel data-driven approach for analyzing synchrotron Laue X-ray microdiffraction scans based on machine learning algorithms. The basic architecture and major components of the method are formulated mathematically. We demonstrate it through typical examples including polycrystalline BaTiO$_3$, multiphase transforming alloys and finely twinned martensite. The computational pipeline is implemented for beamline 12.3.2 at the Advanced Light Source, Lawrence Berkeley National Lab. The conventional analytical pathway for X-ray diffraction scans is based on a slow pattern by pattern crystal indexing process. This work provides a new way for analyzing X-ray diffraction 2D patterns, independent of the indexing process, and motivates further studies of X-ray diffraction patterns from the machine learning prospective for the development of suitable feature extraction, clustering and labeling algorithms.Comment: 29 pages, 25 figures under the second round of review by Acta Crystallographica

Mesoscale constitutive behavior of ferroelectrics

The main goal of this study is the in-situ investigation of the ferroelectric domain structure inside polycrystalline BaTiO3 under thermo-electro-mechanical loading conditions. The outcome is two-fold: (i) the characterization techniques were improved to study the polycrystalline ferroelectrics in the mesoscale; and (ii) the texture, lattice strain and volume fraction of domains were tracked under applied electric field and mechanical stress. Two novel synchrotron-based characterization techniques, three-dimensional X-ray diffraction (3-D XRD) and Scanning X-ray Microdiffraction (ySXRD) were used in this study. The methodology and standards in both techniques differ from each other and the present study provides a framework to bridge these techniques. Although these methods have been developed earlier, their application and adaptation to ferroelectrics required some care. For instance, diffraction spots often overlapped and made it difficult to identify individual domains and/or grains. In order to eliminate the spot overlap, the polycrystalline BaTiO3 sample was heated above the Curie temperature where the (tetragonal) domains disappear and attain the orientation of the grain. Next, the sample was cooled slowly to the room temperature and the evolution of the ferroelectric domains was studied at temperature and under electric field. The orientation relationships, volume fractions and lattice strain evolution of 8 domain systems were studied. Whereas the orientation of the domains remained unchanged under electric field, the fraction of the energetically favorable domain variants increased. Due to local constraints, complete switching from one domain variant to another was not observed. The misorientation angles between domain variants slightly deviated from the theoretical value (=89.4y) by 0.2-0.3y. The deviation angle can be explained with the phase-matching angle developed during the cubic-tetragonal phase transformation to maintain strain compatibility of neighboring domains. The multiscale strain evolution of ferroelectric domains in a polycrystal was investigated quantitatively for the first time. Under electric field, lattice strains of up to 0.1% were measured along the applied field direction. The present study offers a framework to characterize the polycrystalline materials with complex twin structures. By using the methodology described in this study, 3D-XRD and ySXRD techniques can be employed to study texture and lattice strain evolution in polycrystalline materials in the mesoscale

Microstructure and processing effects on stress and reliability for through-silicon vias (TSVs) in 3D integrated circuits

Copper (Cu) Through-silicon via (TSV) is a key enabling element that provides the vertical connection between stacked dies in three-dimensional (3D) integration. The thermal expansion mismatch between Cu and Si induces complex stresses in and around the TSV structures, which can degrade the performance and reliability of 3DICs and are key concerns for technology development. In this dissertation, the effects of Cu microstructure and processing conditions on the stress characteristics and reliability of the TSV structure are studied. First, the stress characteristics of Cu TSV structures are investigated using the substrate curvature method. The substrate curvature measurement was supplemented by microstructure and finite element analyses (FEA) to investigate the mechanisms for the linear and nonlinear stress-temperature behaviors observed for the TSV structure. Implications of the near surface stress on carrier mobility change and device keep-out zone (KOZ) are discussed. Second, via extrusion, an important yield and reliability issue for 3D integration, is analyzed. Synchrotron x-ray microdiffraction technique was introduced for direct measurements of local stress and material behaviors in and around the TSV. Local plasticity near the top of the via was observed which provided direct experimental evidence to support the plasticity mechanism of via extrusion. An analytical model and FEA were used to analyze via extrusion based on local plasticity. Next, the effect of Cu microstructure effect on the thermomechanical behaviors of TSVs is investigated. The contribution from grain boundary and interfacial diffusion on via extrusion and the relaxation mechanisms are discussed. Potential approaches to minimize via extrusion are proposed. Finally, the stress characteristics of 3D die stack structures are studied using synchrotron x-ray microdiffraction. High resolution stress mappings were performed and verified by finite element analysis (FEA). FEA was further developed to estimate the stress effect on device mobility changes and the warpage of the integrated structure.Materials Science and Engineerin

A laboratory based system for Laue micro x-ray diffraction

A laboratory diffraction system capable of illuminating individual grains in a polycrystalline matrix is described. Using a microfocus x-ray source equipped with a tungsten anode and prefigured monocapillary optic, a micro-x-ray diffraction system with a 10 mum beam was developed. The beam profile generated by the ellipsoidal capillary was determined using the"knife edge" approach. Measurement of the capillary performance, indicated a beam divergence of 14 mrad and a useable energy bandpass from 5.5 to 19 keV. Utilizing the polychromatic nature of the incident x-ray beam and application of the Laue indexing software package X-Ray Micro-Diffraction Analysis Software, the orientation and deviatoric strain of single grains in a polycrystalline material can be studied. To highlight the system potential the grain orientation and strain distribution of individual grains in a polycrystalline magnesium alloy (Mg 0.2 wt percent Nd) was mapped before and after tensile loading. A basal (0002) orientation was identified in the as-rolled annealed alloy; after tensile loading some grains were observed to undergo an orientation change of 30 degrees with respect to (0002). The applied uniaxial load was measured as an increase in the deviatoric tensile strain parallel to the load axis (37 References)

Microstructural characterization of a plasma sprayed ZrO2-Y2O3-TiO2 thermal barrier coating

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The use of plasma sprayed ceramic coats as thermal barrier coatings (TBCs) for the protection of metallic structures and equipment from severe thermal, abrasive and corrosive conditions has been documented extensively in the last two decades. The state-of-the-art TBCs consist of a double layer coat. a top ceramic layer and an intermediate bond coat (MCrAIY, M=Ni, Co, Fe) deposited on the alloy substrate. Zirconia, both stabilized and partially stabilized with different oxides has been used as the ceramic top coat due to its low thermal conductivity and low thermal expansion coefficient. Studies of the microstructure of the TBCs have shown aspects that can help the understanding of the properties of the coating. The ternary system ZrOz-Y203-TiCz is believed to offer improved properties when it is compared to Zr02-Y203. However, the use of &02-Y203-Ti02 as TBCs, a major part of this work, is not widely reported in the literature. The purpose of this thesis was to study the microstructure of a plasma sprayed ZrOrY203-TiO2 TBC using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Transmission Electron Microscopy (TEM). The evolution of the Zr41_phase distribution in the ceramic coat was followed by XRD after different heat treatments, with the finding that the cooling rate plays a decisive role in the final Zr42 phase composition. SEM studies allowed a description of the lamellae structure of the Zr02-Y203-TiOz coating. The evolution of the morphology, porosity and crack distribution in the coat after different thermal treatments were followed by SEM. Evidence of incipient sintering is observed in Zr02-Y203-Ti02 coats heated at temperatures higher than 1200 °C. This should lead to poor coating performance. EDS analysis revealed an heterogeneous distribution of titanium through the oating. A detailed microstructural characterization of the as-sprayed coating was done using TEM. Microstructural features such as micro-twins, antiphase-boundaries and mottled morphology associated with "non-transformable" tetragonal ZrO2 phase were identified. It is believed that these microstructural elements promote toughening and thermal stress relief mechanisms that provide the coating with the erosion and thermal shock resistance required for a TBC. The presence of TiO2 is linked to a higher proportion of tetragonal ZrO2 in the Zr02-Y203-Ti02 coating, therefore improved properties of the coating are expected. The addition of TiO2 promotes grain growth and decreases the final density in pressed and sintered Zr02-Y203-TiO2 powders. The results obtained are a contribution to the understanding of the microstructure of TBCs and to the sparse knowledge base of the ZrOrY2O3-TiO2 coatings. Further work should be done in the characterization of the ZrO2-Y2O3-Ti42 coatings and the study of its stability under different conditions in order to determine the real potential of this material offers as an alternative to the better known ZrOrY203 TBC.This work is funded by the British Council and the Consejo Nacional de Investigaciones Cientificas y Tecnolögicas (CONICIT), Venezuela

Comprehensive study of dynamic curing effect on tablet coating structure

International audienceThe dissolution method is still widely used to determine curing end-points to ensure long-term stability of film coatings. Nevertheless, the process of curing has not yet been fully investigated. For the first time, joint techniques were used to elucidate the mechanisms of dynamic curing over time from ethylcellulose (Aquacoat (R))-based coated tablets. X-ray micro-computed tomography (X mu CT), Near Infrared (NIR), and Raman spectroscopies as well as X-ray microdiffraction were employed as non-destructive techniques to perform direct measurements on tablets. All techniques indicated that after a dynamic curing period of 4 h, reproducible drug release can be achieved and no changes in the microstructure of the coating were any longer detected. X mu CT analysis highlighted the reduced internal porosity, while both NIR and Raman measurements showed that spectral information remained unaltered after further curing. X-ray microdiffraction revealed densification of the coating layer with a decrease in the overall coating thickness of about 10 pm as a result of curing. In addition, coating heterogeneity attributed to cetyl alcohol was observed from microscopic images and Raman analysis. This observation was confirmed by X-ray microdiffraction that showed that crystalline cetyl alcohol melted and spread over the coating surface with curing. Prior to curing, X-ray microdiffraction also revealed the existence of two coating zones differing in crystalline cetyl alcohol and sodium lauryl sulfate concentrations which could be explained by migration of these constituents within the coating layer. Therefore, the use of non-destructive techniques allowed new insights into tablet coating structures and provided precise determination of the curing end-point compared to traditional dissolution testing. This thorough study may open up new possibilities for process and formulation control

Coherent X-ray Diffractive Imaging; applications and limitations

The inversion of a diffraction pattern offers aberration-free diffraction-limited 3D images without the resolution and depth-of-field limitations of lens-based tomographic systems, the only limitation being radiation damage. We review our experimental results, discuss the fundamental limits of this technique and future plans.Comment: 7 pages, 8 figure

Laser cladding of quasi-crystal-forming Al-Cu-Fe-Bi on an Al-Si alloy substrate

We report here the results of an investigation aimed at producing coatings containing phases closely related to the quasi-crystalline phase with dispersions of soft Bi particles using an Al-Cu-Fe-Bi elemental powder mixture on Al-10.5 at. pct Si substrates. A two-step process of cladding followed by remelting is used to fine-tune the alloying, phase distribution, and microstructure. A powder mix Al64CU22.3Fe11.7Bi2 of has been used to form the clads. The basic reason for choosing Bi lies in the fact that it is immiscible with each of the constituent elements. Therefore, it is expected that Bi will solidify in the form of dispersoids during the rapid solidification. A detailed microstructural analysis has been carried out by using the backscattered imaging mode in a scanning electron microscope (SEM) and transmission electron microscope (TEM). The microstructural features are described in terms of layers of different phases. Contrary to our expectation, the quasi-crystalline phase could not form on the Al-Sisubstrate. The bottom of the clad and remelted layers shows there growth of aluminum. The formation of phases such as blocky hexagonal Al-Fe-Si and a ternary eutectic (Al + CuAl2 + Si) have been found in this layer. The middle layer shows the formation of long plate-shaped Al13Fe4 along with hexagonal Al-Fe-Si phase growing at the periphery of the former. The formation of metastable Al-Al6Fe eutectic has also been found in this layer. The top layer, in the case of the as-clad track, shows the presence of plate-shaped Al13Fe4along with a 1/1 cubicrational approximant of a quasi-crystal. The top layer of the remelted track shows the presence of a significant amount of a 1/1 cubicrational approximant. In addition, the as-clad and remelted microstructures show a fine-scale dispersion of Bi particles of different sizes formed during monotectic solidification. The remelting is found to have a strong effect on the size and distribution of Bi particles. The dry-sliding wear properties of the samples show the improvement of wear properties for Bi-containing clads. The best tribological properties are observed in the as-clad state, and remelting deteriorates the wear properties. The low coefficient offriction of the as-clad and remelted track is due to the presence of approximant phases. There is evidence of severe subsurface deformation during the wear process leading to cracking of hard phases and a change in the size and shape of soft Bi particles. Using these observations,we have rationalized possible wear mechanisms in the Bi-containing surface-alloyed layers

STUDY OF STRUCTURAL, THERMAL, HYDROGENATION AND COMPOSITIONAL PROPERTIES OF NI-BASED AMORPHOUS MEMBRANES USING EXPERIMENTAL AND COMPUTATIONAL METHODS

Hydrogen is considered as a promising source of energy because of its properties such as abundant availability, high energy conversion efficiency, low-density, solid-state storage potential, and most importantly zero emission from energy conversion devices, such as fuel cell. End product from hydrogen internal combustion engine is just water vapor. Hydrogen can be generated from various different sources and can be stored in solid, liquid and gaseous forms. One of the methods of producing hydrogen is in the form of syngas (mixture of methane, CO, CO2 and water vapor) obtained from coal gasification in a water shift reactor using hydrogen selective membrane. Palladium is a very expensive material and when used in its crystalline form, it is prone to hydrogen embrittlement during prolonged exposure to hydrogen at high temperature and pressure. It is important to find a cheaper alternative with excellent hydrogen permeation properties. Amorphous alloy membranes, such as NiNbZr membranes are good contenders due to their high glass forming ability and the hydrogen permeation properties comparable to Pd or Pd alloys. In spite of significant research performed on these glassy alloy materials, there is still a lack of understanding of the nature of the local atomic order involving formation of icosahedra, and the hydrogen interaction mechanisms with them. It is generally accepted that the multicomponent amorphous alloy membranes are most effective in hydrogen permeation. However, the effect of alloying element addition on cluster formation, permeation mechanisms, and thermal properties of certain membranes are also not fully understood.A combined experimental and computational approach is used to understand the undiscovered properties of Ni-Nb-Zr membranes. XRD studies on melt spun ribbons confirmed amorphicity of these membranes in all the conditions (at 25oC and at 400oC under hydrogen pressure) at the Molecular Foundry of Lawrence Berkeley National Laboratory. Depth profile analysis using the X-ray photoelectron spectroscopy (XPS) gave an insight in to the difference in the surface composition of both the sides of membranes and the effect alloy composition on the same. Addition of alloying elements such as V, Fe, Ti to the NiNbZr alloys are expected to alter thermal properties of these membranes because of difference in atomic size. We selected melt spun NiNbZr alloy with Fe additions for hydrogen solubility studies by volumetric methods. Density functional theory based Molecular dynamics (DFT-MD) studies revealed formation of icosahedral clusters. Upon hydrogenation, hydrogen atoms were seen to interact with these clusters in three different ways: (i) occupation of interstitial sites, (ii) substitution of an atom from a cluster, and (iii) replacement of the central atom. These results helped in understanding of hydrogen permeation process. Effect of addition of alloying elements on the structural and permeation properties showed how affinity towards hydrogen and size of certain alloying elements can affect icosahedral clusters in the membrane. Exploratory studies on developing numerous multicomponent alloys is a rather impossible task using melt spin spinning method. This is due to the fact that the bulk alloy needs to be fabricated first and annealed, then melt spinning needs to be performed, finally the hydrogen permeation studies that are very laborious, even to determine a single alloy property. An alternative expedient method is to produce numerous thin film alloys by PVD deposition on a Si single crystal wafer. Thus, thin film of NiNbZr with Ta additions on Si wafer substrate were fabricated at the CINT, Los Alamos National Laboratory that yielded numerous alloy compositions. In this study, we determined (i) stability, amorphicity and surface properties of amorphous melt spun ribbons of NiNbZr alloy membranes by using x-ray diffraction and x-ray photoelectron spectroscopy, thermal properties of NiNbZrFe, NiNbZrTi and NiNbZrV alloy membranes by differential scanning calorimetry and hydrogen solubility of NiNbZrFe alloy membrane using Sievert’s volumetric method, (ii) developed different compositions of thin films of NiNbZrTa alloys on Si substrate by using PVD methods, synchrotron x-ray diffraction to confirm their amorphicity and did chemical analyses by SEM-EDS system and (iii) developed theoretical models using Density Functional Theory based Molecular dynamics (DFT-MD) studies to understand icosahedral clustering and hydrogen interaction on a local atomic order

Surface modification of bioceramics: chemically enhanced laser surface microstructuring of hydroxyapatite

PhDBioceramics have been developed for implants to repair damaged tissues of the human musculo-skeletal system. The clinical success of a bioceramic implant depends largely on the chemical response at the implant interface in addition to the sufficiency of the mechanical properties for the application. The present study combines the developments in the fields of bioceramic materials and laser surface micro structuring of materials. Bioceramic hydroxyapatite powders (HA, Formula: CaIO(PO4)6(OH)2) have been produced by emulsion technology and freeze-drying methods exhibiting BET specific surface areas >148 m2 /g and particle sizes <13 nrn prior to thermal treatment. The powder yield has been doubled using an increased reaction temperature of 25 *C from 17 *C, with a small increase (< 4nm) in the average particle size. HA discs that were >95.5 % dense have been achieved after isostatic pressing with pressure of 0.59 MPa and pressurelesss intering at 1200 *C for 2 hours. No chemical decomposition was detected using X-ray Diffraction Analysis (XRD). Methods of chemically enhanced laser-assisted etching have been developed to produce microstructural features on the surface of bioceramic HA discs that were 78.5 % dense (2482.95 kr , /M3 measured density). The use of 10 MPa SF6 at laser fluencies in the range of 14.50-15.20 W/M2 produced a columnar topography with individual structures featuring 10-20 pm height and 8-12 pm width as characterised by Scanning Electron Microscopy (SEM). Chemical characterisation by X-ray microdiffraction, Energy Dispsersive, X-ray analysis (SEM-EDS), Fourier Transformed Infrared spectroscopy (FTIR) and Raman spectroscopy (Raman) found the microtopography to be composed of fluorine-substituted HA (FHA). Alternatively the use of 80 MPa NH3 at laser fluencies in the range of 17.17-18.50 kj/m 2 produced an irregular surface of scattered porous hillocks that remained chemically unchanged in composition but exhibited four times as many surface hydroxyl groups. In both cases the mechanical and chemical stability of the bulk composition is maintained and the surface of increased surface area, in addition to the presence of concavities and pores is likely to be of enhanced osteoconductivity.IRC in Biomaterial