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49 records found
1.
Zaafarani, N., D. Raabe, et al. (2006). "Three-dimensional investigation of the texture and microstructure below a nanoindent in a Cu single crystal using 3D EBSD and crystal plasticity finite element simulations." Acta Materialia 54(7): 1873-1876.
This paper reports a three-dimensional (3D) study of the microstructure and texture below a conical nanoindent in a (1 1 1) Cu single crystal at nanometer-scale resolution. The experiments are conducted using a joint high-resolution field emission scanning electron microscopy/electron backscatter diffraction (EBSD) set-up coupled with serial sectioning in a focused ion beam system in the form of a cross-beam 3D crystal orientation microscope (3D EBSD). The experiments (conducted in sets of subsequent (112) cross-section planes) reveal a pronounced deformation-induced 3D patterning of the lattice rotations below the indent. In the cross-section planes perpendicular to the (1 1 1) surface plane below the indenter tip the observed deformation-induced rotation pattern is characterized by an outer tangent zone with large absolute values of the rotations and an inner zone closer to the indenter axis with small rotations. The mapping of the rotation directions reveals multiple transition regimes with steep orientation gradients and frequent changes in sign. The experiments are compared to 3D elastic–viscoplastic crystal plasticity finite element simulations adopting the geometry and boundary conditions of the experiments. The simulations show a similar pattern for the absolute orientation changes but they fail to predict the fine details of the patterning of the rotation directions with the frequent changes in sign observed in the experiment. Also the simulations overemphasize the magnitude of the rotation field tangent to the indenter relative to that directly below the indenter tip.
2.
Zaefferer, S. (2003). "Investigation of the Correlation between Texture and Microstructure on a Submicrometer Scale in the TEM." Advanced Engineering Materials 5(8): 607-614.
3.
Zaefferer, S. (2003). Microstructural Characterization of Multiphase Steels. Thermec' 2003, Leganés, Madrid, Spain, Trans Tech Publications Ltd.
Automatic Crystal Orientation Mapping (ACOM) in the SEM and orientation determination in the TEM are used for a precise and detailed characterization of the microstructure of a multiphase TRIP steel. Besides austenite, bainite plays an important role for the functioning of the TRIP effect. Therefore particular emphasis is placed on the difficult discriminaation of bainite and ferrite.The existence of massive bainite is concluded from the interpretation of characteristic orientation gradients in the ferrite and a Kurdjumov-Sachs orientation relationship of bainite and austenite. The bainite formation is explained by a reversion of the g-a phase boundary movement during austenization and subsequent tempering at bainite formation temperature.
4.
Zaefferer, S. (2004). "The Electron Backscatter Diffraction Technique – A Powerful Tool to Study Microstructures by SEM." The JEOL News 39(1): 10-15.
In the last 10 years the electron backscatter diffraction (EBSD) technique has developed into a powerful tool for the crystallographic analysis of materials in the scanning electron microscope. In particular the emergence of computer algorithms for the fully automated analysis of diffraction patterns has pushed the technique to develop into a new kind of scanning microscopy technique, known as “orientation imaging microscopy, OIM1” or “automatic crystal orientation mapping, ACOM”. The ACOM technique is based on the consecutive acquisition of electron diffraction patterns obtained from every point of a scan grid on a flat surface of a steeply inclined sample in the SEM. The automatic analysis of these EBSD patterns yields for every scan point the crystallographic orientation and phase and a value indicating the quality of the diffraction pattern. From these data the microstructure of the scanned area can be reconstructed. The resulting crystal orientation maps give a vast amount of information on the sample, including kind and distribution of different phases, size, form and defect condition of grains, kind and position of grain boundaries, local crystal orientation and misorientation distribution (texture) and others more. Furthermore, EBSD can be used to investigate the structure of crystals, i.e. lattice symmetry and lattice parameters and may therefore take over a large amount of crystallographic work that was performed before by TEM. The EBSD technique usually requires less complicated sample preparation and allows the observation of much larger areas, yet with a quite high spatial resolution. Although the EBSD technique can be applied with good success on a standard tungsten filament SEM it profits enormously - in terms of spatial resolution and orientation accuracy - from using a thermal field emission gun instrument with a high beam current. The present text briefly describes some of the physical fundamentals and the practical set-up of the technique before it presents a couple of application examples that illustrate some of its possibilities. All examples stem from problems of physical metallurgy – the author's field of expertise – although the technique is also intensively applied to the study of non-metallic, crystalline materials like semiconductors, ceramics and minerals.
5.
Zaefferer, S. (2005). Application of orientation microscopy in SEM and TEM for the study of texture formation during recrystallisation processes. Textures of Materials - ICOTOM 14, Leuven, Belgium, Trans Tech Publications.
Orientation microscopy in TEM and SEM is a particularly well suited tool to study recrystallisation processes because these are always associated with orientation and microstructure changes. The present work discusses the possibilities and limits of the TEM and SEM based techniques and illustrates their use by means of 3 different examples. The examples include studies on nucleation mechanisms of primary recrystallisation where the techniques meet their limits in spatial resolution. The problem of in-situ observations of annealing processes is discussed and it is shown how recrystallisation simulation techniques based on experimental data may be used. Furthermore the new technique of 3-dimensional EBSD in a focused-ion-beam (FIB) SEM is presented with one example. Finally, the statistical analysis of very large orientation data sets is
discussed by an example of secondary recrystallisation in electrical steels.
6.
Zaefferer, S. and U. Glatzel (2002). Orientation Relationship of Phases in an Oxidation Protection Coating on a Ni-Based Superalloy Single Crystal. ICOTOM 13, Seoul, Korea, Trans Tech Publications Inc.
Nickel-base superalloys with y/y1 microstructure are state of the art material for singe crystal turbine blades. They can be coated with aluminum and subsequently diffusion annealed in order to increase their oxidation resistance. EBSD and EDX measurements were used to determine the different phases in the diffusion zone and to gather information about the diffusion and phase transformation mechanisms. It was found that during heat treatment, aluminum diffuses from the coating in to the L12ordered Ni3Al substrate crystal and forms a complex precipitation zone which consists of several different phases. A large amount of crystals in this zone belongs to the B2 ordered NiAl phase. These crystals show a clear and sharp orientation relationship with the Ni3Al substrate. It is concluded that nucleation of the new crystals in the substrate proceeds by a form of coherent (or semi-coherent) precipitation. This assumption is supported by calculations of the lattice misfit between the parallel crystal planes in both phases.
7.
Zaefferer, S., J. Konrad, et al. (2005). 3D-Orientation Microscopy in a Combined Focused Ion Beam (FIB) - Scanning Electron Microscope: A New Dimension of Microstructure Characterisation. Microscopy Conference, Davos, Switzerland.
8.
Zaefferer, S., J. Ohlert, et al. (2004). "A study of microstructure, transformation mechanisms and correlation between microstructure and mechanical properties of a low alloyed TRIP steel." Acta Materialia 52: 2765-6778.
Differently heat treated samples of a low alloyed TRIP steel have been investigated using electron diffraction techniques in SEM and TEM. Aim was, first, to discriminate the microstructure constituents, austenite, ferrite, bainite, and martensite, second to gain information on the γ–α phase transformation mechanisms and third to correlate the mechanical properties and the microstructure of the samples. Bainite always occurs in conjunction with an orientation gradient in the surrounding ferrite matrix. It consists of fine lamellae of ferrite and austenite which show a sharp Kurdjumov–Sachs orientation relationship with each other. This was interpreted in terms of a displacive bainite formation mechanism. The microstructure is formed by growth of γ-grains during intercritical annealing and shrinking of these grains during the subsequent cooling without nucleation of new a-grains. The transformation first occurs reconstructively into ferrite and then, at lower temperature, displacively into bainite. The mechanical properties of differently heat treated samples are most strongly influenced by the amount and distribution of carbon in the retained austenite and by the degree of recovery in bainite and austenite.
9.
Zajac, S., V. Schwinn, et al. (2005). Characterisation and Quantification of Complex Bainitic Microstructures in High and Ultra-High Strength Linepipe Steels. Proceedings of the International Conference on Microalloying for New Steel Processes and Applications, Donostia-San Sebastian, Basque Country, Spain, Trans Tech Publications.
This paper provides a detailed description of complex bainitic microstructures obtained during the recent development of low carbon linepipe steels with strengths in the range of X100 to X120. New experimental techniques based on a high resolution FEG-SEM and EBSD have been used to characterise and quantify the mixture of ultrafine bainitic ferrite and nanosize second phases in these steels. It was found that the occurrence of incomplete transformation generates new, previously unexplored bainitic microstructures with a wealth of microstructural features that is beyond classification based on conventional concepts. Clear differences in distributions of boundary misorientations and effective grain size were noted between upper, lower and granular bainites. Based on these results a new classification scheme and definition of bainite is proposed.
10.
Zhai, H.-Y., I. A. Rusakova, et al. (2001). "Study of Strain Relaxation of YBa2Cu3O7-δFilm Grown on SrTiO3 and LaAlO3." IEEE Transactions On Applied Superconductivity 11(1): 3461-3464.
11.
Zhang, N. and W. Tong (2004). "An experimental study on grain deformation and interactions in an Al-0.5 % Mg multicrystal." International Journal of Plasticity 20(3): 523-542.
Heterogeneous plastic deformation behavior of a coarse-grained Al-0.5%Mg multicrystal was investigated experimentally at the individual grain level. A flat uniaxial tensile specimen consisting of a single layer of millimeter-sized grains was deformed quasi-statically up to an axial strain of 15% at room temperature. The initial local crystallographic orientations of the grains and their evolutions after 5, 12, and 15% plastic strains were measured by electron backscattered diffraction pattern analysis in a scanning electron microscope. The local inplane plastic strains and rigid body rotations of the grains were measured by correlation of digital optical video images of the specimen surface acquired during the tensile test. It is found that both intergranular and intragranular plastic deformation fields in the aluminum multicrystal specimen under uniaxial tension are highly heterogeneous. Single or double sets of slipplane traces were predominantly observed on the electro-polished surfaces of the millimetersized grains after deformation. The active slip systems associated with these observed slipplane traces were identified based on the grain orientation after deformation, the Schmid factor, and grain interactions in terms of the slip-plane trace morphology at grain boundaries. It is found that the aluminum multicrystal obeys neither the Sachs nor the Taylor polycrystal deformation models but deforms heterogeneously to favor easy slip transmission and accommodation among the grains.
12.
Zhang, P., X. Ren, et al. (2005). "Superplasticity mechanism of duplex stainless steels." Beijing Keji Daxue Xuebao (Journal of University of Science and Technology Beijing) 27(1): 68-71.
The superplasticity mechanism of duplex stainless steels was studied mainly by means of crystallography. On this basis, the Electron Back Scatter Diffraction (EBSD) system was used to obtain the orientation distribution, Tango-mapping and Mambo-pole figures. Microstructural studies associated with transmission electron micrographs observed in the specimens during superplastic deformation suggest that superplastic process occurs mainly by strain-induced phase transformation and dynamic recrystallization, grain boundary sliding and grain reorientation mechanism.
13.
Zhang, S. Q., S. Karato, et al. (2000). "Simple Shear Deformation of Olivine Aggregates." Tectonophysics 316(1-2): 133-152.
14.
Zhang, X.-M., Y.-X. Du, et al. (2003). "Development of cube texture in multistage annealing of high purity aluminum foils." Transactions of the Nonferrous Metals Society of China 13(6): 1389-1393.
The development of cube texture ({001} <100>) in high purity (99.99%) aluminum foils in multistage annealing was investigated by ODF and EBSD It is found that a multistage annealing process can strengthen cube texture markedly, and that each stage of the multistage annealing plays an important eigen role in nucleation and growth of the cube orientation grains. The cube orientation grain nucleates preferably at 180 deg C because of its low activation energy of nucleation, the cube nuclei grow favorably at 400 deg C because of the anisotropy of 40 deg <111> growth, and the cube texture is further strengthened at 550 deg C and becomes predominant because of favorable bigger grain sizes.
15.
Zhang, Y. D., C. Esling, et al. (2005). Solid state phase transformations under high magnetic fields in a medium carbon steel. Textures of Materials - ICOTOM 14, Leuven, Belgium, Trans Tech Publications.
High magnetic fields were applied to the austenite to proeutectoid transformation and tempering process in a 42CrMo steel. The thermodynamic and kinetic effects of the high magnetic field on the austenite decomposition show that it can obviously increase the amount of the product ferrite and accelerate the transformation by enhancing the Gibbs free energy difference between the parent and product phases. Moreover, the magnetic field can considerably lower the amount of low angle misorientations of ferrite in pearlite colonies and obviously increase the frequency of Σ3-29 coincidence boundaries, especially Σ3 boundaries, of the ferrite. But it has no obvious effect on crystallographic orientation distribution. When the field is applied to the high temperature tempering process, it can effectively prevent the directional growth of cementite along martensite plate boundaries and twin boundaries by increasing both the cementite/ferrite interfacial energy and the magnetostrictive strain energy. Finally, particle-like cementite is obtained. The magnetic field also obviously retards the formation and growth of the ‘distortion-free’ regions of the matrix.
16.
Zhang, Y. D., G. Vincent, et al. (2005). The effects of a high magnetic field on microstructure, grain boundary structures and texture in a medium carbon steel under different cooling rates. Textures of Materials - ICOTOM 14, Leuven, Belgium, Trans Tech Publications.
A 12-Tesla magnetic field was applied during the transformation from austenite to ferrite and then pearlite in a medium plain carbon steel at two different cooling rates. Results show that when cooling is slow, the magnetic field shows an effect of promoting proeutectoid ferrite grains to grow along the field direction that results in an elongated grain microstructure. However, when cooling is fast, the magnetic field mainly shows an effect of reducing the amount of low angle misorientations and increasing the amount of CSL boundaries. In addition, the magnetic field exhibits a slight enhancement of the <001> texture component in the direction that is perpendicular to the field direction (TFD).
17.
Zhang, Y., C. He, et al. (2004). "New microstructural features occurring during transformation from austenite to ferrite under the kinetic influence of magnetic field in a medium carbon steel." Journal of Magnetism and Magnetic Materials 284: 287-293.
The effects of magnetic field on nucleation barrier of the phase transformation from austenite to ferrite at different cooling rates in 42CrMo steel have been investigated. The microstructures of ferrite and pearlite aligned along the magnetic field direction (parallel to the hot-rolling direction) are obtained at a cooling rate of 10 °C/min, resulting from the kinetic effects of the applied magnetic field during cooling and the microstructural influences of an inhomogeneous deformation occurring during the previous hot rolling. In this case, the formation of ferrite grains at higher temperatures is attributed mainly to the preferential nucleation at austenite boundaries. However, a fairly uniform microstructure of randomly distributed ferrite and pearlite is formed at a high cooling rate of 46 °C/min in the magnetic field of 14 T, as a result of both intergranular and intragranular nucleation at relatively low temperatures. Probing into this issue is helpful to gain a better understanding of kinetic influences of magnetic field on the phase transformation from austenite to ferrite.
18.
Zhang, Z. F. and Z. G. Wang (2003). "Fatigue-cracking characteristics of a copper bicrystal when slip bands transfer through the grain boundary." Materials Science and Engineering A 343(1-2): 308-313.
We reported the fatigue cracking characteristics of a special copper bicrystal with a tilt Σ 19b grain boundary (GB) and a coplanar primary slip system between the two grains. It is found that the primary slip bands of the two adjacent grains have a good continuation across the GB on the four surfaces of the bicrystal specimen in the axial plastic strain range of 1.5×10-4 – 2.13×10-3. It indicates that the surface slip bands had transferred through the GB during cyclic deformation. When cyclic plastic strain was continued to be applied on the bicrystal specimens, fatigue cracks always initiated and propagated along the GB at all the applied strain amplitudes. By using electron channeling contrast (ECC) technique in scanning electron microscopy (SEM), the dislocation patterns near the GB of the bicrystal were observed. The ladder-like persistent slip bands (PSBs) did not transfer through the GB continuously, no matter what the surface or the common primary slip plane of the bicrystal. Instead, a dislocation affected zone (DAZ) or piling-up of dislocations near the GB was observed. Based on the results above, the fatigue cracking mechanism of the bicrystal was discussed and the GB cracking was attributed to the difference in the slip directions of the two adjacent grains.
19.
Zhao, J.-C. (2004). "Reliability of the diffusion-multiple approach for phase diagram mapping." Journal of Materials Science 39: 3913-3925.
The diffusion-multiple approach can be used to map phase diagrams at an efficiency orders of magnitude faster than the conventional equilibrated alloy method. This paper addresses a concern about the reliability of the results, especially whether the data obtained from diffusion multiples can produce reliable equilibrium phase diagrams. The following topics will be discussed: (a) establishment of local equilibrium at the phase interfaces, (b) X-ray interaction volume vs. thickness of the phases (microprobe related issues), (c) reliability of phase diagrams from equilibrated alloys, (d) usefulness of electron backscatter diffraction, (e) impurity-induced stabilization of metastable phases, and, (f) missing phase situations. A direct comparison of several ternary systems obtained from both diffusion multiples and equilibrated alloys was made. The good agreement between them clearly demonstrates the reliability of phase diagrams determined from diffusion multiples.
20.
Zhao, J.-C., B. P. Bewlay, et al. (2001). "Determination of Nb–Hf–Si phase equilibria." Intermetallics 9: 681-689.
Phase equilibria of Nb–Hf–Si at 1500 °C have been investigated for the metal-rich end of the ternaryphase diagram using scanning electron microscopy, electron probe microanalysis, and electron backscatter diffraction analysis. An isothermal section at 1500 °C was constructed for this ternary system based on experimental data from 11 alloys heat treated at 1500 °C for 100 h. Phase equilibria between the following silicides, Nb(Hf)5Si3, Hf(Nb)5Si3, Nb(Hf)3Si, Hf(Nb)2Si, Hf(Nb) 3Si2, Hf(Nb)5Si4, Hf(Nb)Si, Nb(Hf)Si2, and two metal-rich solid solutions, β(Nb,Hf,Si) and α(Hf,Nb,Si) are described.
21.
Zhao, J.-C., M. R. Jackson, et al. (2002). "A Diffusion-Multiple Approach for Mapping Phase Diagrams, Hardness, and Elastic Modulus." JOM 54(7): 42-45.
22.
Zhao, J.-C., M. R. Jackson, et al. (2002). "A Diffusion Multiple Approach for the Accelerated Design of Structural Materials." MRS Bulletin 27(4): 324-329.
A diffusion multiple is an assembly of three or more different metal blocks, an intimate interfacial contact, that is subjected to a high temperature to allow thermal interdiffusion. The power of using a diffusion multiple approach in the efficient mapping of phase diagrams and materials properties for multi-component alloy systems is illustrated in this article using several examples. It is now possible to map phase diagrams and materials properties at an efficiency three orders of magnitude higher than the conventional one-alloy-at-a-time approach. With this high efficiency, many critical materials data that otherwise would be too time-consuming and expensive to acquire can be obtained and employed to accelerate our understanding of a system's materials physics and chemistry. It is possible that coupling the diffussion multiple approach with the CALPHAD (calculation of phase diagrams) method will have a significant impact on the computational design of materials.
23.
Zhao, J.-C., M. R. Jackson, et al. (2003). "Determination of the Nb-Cr-Si phase diagram using diffusion multiples." Acta Materialia 51(20): 6395-6405.
A high-efficiency diffusion-multiple approach was employed to determine the phase diagram of the Nb-Cr-Si ternary system which is critical for the design of niobium silicide-based in situ composites. These composites have high potential as a replacement for Ni-base superalloys for jet engine applications. The formation of the Nb(Cr,Si)2 Laves phase is beneficial to the high oxidation resistance of the composites and the Nb-Cr-Si system serves as the base for understanding the Laves phase formation. The results clearly demonstrate the applicability of the diffusion-multiple approach in determining such complex phase diagrams as Nb-Cr-Si which contains 14 phases. Two isothermal sections at 1000 and 1150 elatively C were constructed from the results obtained from diffusion multiples using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and electron backscatter diffraction (EBSD). Three ternary compounds, CrNbSi, (Cr,Nb)6Si5 and (Cr,Nb)11Si8, were observed at both temperatures, and the C14 Laves phase of the Cr-Nb binary system was stabilized by Si to lower temperatures.
24.
Zhao, J.-C., M. R. Jackson, et al. (2004). "Evaluation of phase relations in the Nb-Cr-Al system at 1000 deg C using a diffusion-multiple approach." Journal of Phase Equilibria and Diffusion 25(2): 152-159.
A high-efficiency diffusion-multiple approach was used to map most of the phase relations of the Nb-Cr-Al ternary system at 1000 deg C. This system is very valuable for the design of niobium silicide-based composites. These composites have high potential as a replacement for Ni-base superalloys for jet engine applications. Both Cr and Al are alloying elements for these composites; thus the Nb-Cr-Al phase diagram, especially the stability of the oxidation-resistant Laves phase, is important information for the composite design. A partial 1000 deg C isothermal section was constructed from the results obtained using electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD) from a diffusion multiple made up of Nb, Cr, NbAl3, and NbSi2. The stabilization of the C14 Laves phase by Al dominates the 1000 deg C isothermal section, and the solubility of Al in the C14 Laves phase is as high as approx =45 at.%.
25.
Zhao, J.-C., M. R. Jackson, et al. (2004). "Mapping of the Nb–Ti–Si phase diagram using diffusion multiples." Materials Science and Engineering A 372: 21-27.
A high-efficiency diffusion-multiple approach was employed to map the phase diagram of the Nb–Ti–Si ternary system, which is critical for the design of niobium silicide-based composites. These composites have high potential as a replacement for Ni-base superalloys for jet engine applications. Titanium is one of the most important elements for oxidation resistance and fracture toughness enhancement. Three isothermal sections of Nb–Ti–Si at 1000, 1150 and 1200 °C were constructed from the results obtained from diffusion multiples using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and electron backscatter diffraction (EBSD). Extremely high solubility of Nb in Ti5Si4 (up to ~46 at.% Nb at 1200°C, substituting for Ti) was observed.
26.
Zhao, P. and R. A. Holt (2004). Microstructural evolution and micro-texture in Zr-2.5Nb tubes. Fifth Pacific Rim International Conference on Advanced Materials and Processing PRICM-5, Beijing, China, Trans Tech Publications.
Both small experimental extruded tubes and full-size pressure tubes were examined using scanning electron microscope/electron backscattered diffraction (SEM/EBSD) and transmission electron microscope/selected area diffraction (TEM/SAD). The final microstructures and textures vary with billet microstructure, extrusion temperature and extrusion ratio. Three components in {0002} pole figures were determined. The first component (radial) is produced by a and c+a slip in alpha -grains during extrusion. The second component (transverse) is associated with the elongated alpha -grains with their c-axes parallel to their long dimension. The third component (axial) is produced by beta - alpha phase transformation after extrusion with a preferred variant of the Burgers relationship.
27.
Zhao, Y. M. and J. G. Morris (2005). "Comparison of the Texture Evolution of Direct Chill and Continuous Cast AA5052 Hot Bands during Isothermal Annealing." Metallurgical and Materials Transactions A 36A(9): 2505-2515.
As-received commercial direct chill cast (DC) and continuous cast (CC) AA5052 hot bands were isothermally annealed at different temperatures. The variations of electrical resistivity, hardness, microstructure, and texture of these hot bands during annealing were examined. Texture was investigated by X-ray diffraction. The variation in texture volume fractions with annealing time was quantitatively analyzed by the Johnson-Mehl-Avraini-Kolmogorov (JMAK) equation. The orientation maps of the partially and fully recrystallized samples were characterized by electron backscattered diffraction (EBSD). It was found that electrical resistivity of the CC AA5052 hot band was higher than that of the DC AA5052 hot band. The electrical resistivity of CC AA5052 decreased more significantly than that of DC AA5052 during isothermal annealing. The DC AA5052 hot band was more easily recrystallized than CC AA5052 hot band during annealing. After complete recrystallization, DC AA5052 hot band possessed a stronger cube texture than the CC AA5052 hot band. The texture evolutions of DC and CC AA5052 can be expressed quantitatively by the JMAK equation after the volume fractions of the texture components are calculated by an improved integration method. Annealing temperature had an influence on the n values in the JMAK-type equations. The n values are small at low annealing temperatures.
28.
Zhao, Z., R. Radovitzky, et al. (2005). "A study of surface roughening in fcc metals using direct numerical simulation." Acta Materialia 52(20): 5791-5804.
Grain-scale surface roughening due to plastic straining in polycrystalline aluminum is studied with the aid of a three-dimensional finite-element crystal-plasticity model. An improved understanding of the origin of surface roughening profiles in plastically strained aluminum is sought. Large-scale, Direct Numerical Simulation enables the computation of full-field solutions and the explicit consideration of the deformation of individual crystals as well as of their crystalline texture evolution and interaction with neighboring grains. Simulations are conducted on idealized flat sheet polycrystalline aluminum samples under uniaxial and biaxial loading conditions. The results obtained show that the ensuing surface profiles are controlled by several factors: applied boundary conditions, Taylor factor and shear tendency of the individual grains and the spatial distribution of grain neighborhood orientations. The conditions leading to different ridging profiles, e.g., corrugated and ribbed surface profiles, are discussed.
29.
Zherebtsov, S. V., G. A. Salishchev, et al. (2004). "Production of submicrocrystalline structure in large-scale Ti–6Al–4V billet by warm severe deformation processing." Scripta Materialia 51(12): 1147-1151.
The “abc” deformation method for production of large-scale billets with submicrocrystalline structure was developed. A large billet of Ti–6Al–4V alloy (150-mm diameter × 200-mm length) with a homogeneous submicrocrystalline structure was produced. The refined structure with a grain-subgrain size of about 0.4 µm leads to a substantial mechanical properties improvement
30.
Zhilayaev, A. P., B.-K. Kim, et al. (2002). "Orientation imaging microscopy of ultrafine-grained nickel." Scripta Materialia 46(8): 575-580.
Orientation imagining microscopy was used to measure the distributions of grain boundary misorientations in ultrafine-grained nickel processed by high-pressure torsion and equal-channel angular pressing. Both procedures give high fractions of high-angle boundaries but also higher fractions of low-angle boundaries than anticipated from a random distribution.
31.
Zhilayaev, A. P., G. V. Nurislamova, et al. (2003). "Experimental parameters influencing grain refinement and microstructural evolution during high-pressure torsion." Acta Materialia 51: 753-765.
Pure nickel was selected for a detailed investigation of the experimental parameters influencing grain refinement and microstructural evolution during processing by high-pressure torsion (HPT). Samples were examined after HPT using microhardness measurements, transmission electron microscopy and orientation imaging microscopy. Processing by HPT produces a grain size of ~170 nm in pure Ni, and homogenous and equiaxed microstructures are obtained throughout the samples when they are subjected to at least ~5 whole revolutions under applied pressures of at least ~6 GPa. For these conditions, the distributions of grain boundary misorientations are similar in the center and at the periphery of the samples. A simple model is proposed to explain the development of a homogenous microstructure in HPT.
32.
Zhilyaev, A. P., B.-K. Kim, et al. (2005). "The microstructural characteristics of ultrafine-grained nickel." Materials Science and Engineering A 391: 377-389.
Adetailed investigationwas conducted to evaluate the microstructural characteristics in samples of pure nickel processed using three different procedures of severe plastic deformation (SPD): equal-channel angular pressing (ECAP), high-pressure torsion (HPT) and a combination of ECAP and HPT. Several different experimental techniques were employed to measure the grain size distributions, the textures, the distributions of the misorientation angles and the boundary surface energies in the as-processed materials. It is shown that a combination of ECAP and HPT leads both to a greater refinement in the microstructure and to a smaller fraction of boundaries having low angles of misorientation. The estimated boundary surface energies were higher than anticipated from data for coarse-grained materials and the difference is attributed to the non-equilibrium character of many of the interfaces after SPD processing.
33.
Zhou, Y. X., R. Naguib, et al. (2004). "Development of cube textured Ni-W alloy tapes using powder metallurgy along with high energy ball milling for HTS coated conductors." Superconductor Science and Technology 17(7): 947-953.
Ni based alloys have received considerable attention as the substrates for HTS coated conductors due to improved mechanical properties and reduced magnetization. Powder metallurgy is one of the promising processes for the fabrication of long alloy textured substrates. In this paper, Ni-3 at.% W alloy substrates were prepared by using high purity metal powders as starting materials. The Ni and 3 at.% W powder mixture was high energy ball milled for different periods, isostatically pressed, sintered, rolled and texture annealed. The high energy ball milling process made the powders mix uniformly and the grain sizes decrease significantly, which led to higher boundary energy and residual strain energy. The longer ball milling period resulted in a finer grain size and sharper texture in the substrate, which were confirmed by EBSD and SEM analysis. SEM and AFM observations indicate the surface of textured Ni-3 at.% W substrates is smooth and the roughness value (Rrms) is about 1.126 nm, which is suitable for deposition of buffer layers.
34.
Zhou, Y. X., T. Rizwan, et al. (2003). Growth of cube-textured nickel substrates for HTS coated conductors. High Temp. Superconductivity Group Department of Materials University of Oxford, Oxford OX1 3PH, United Kingdom, Houston, Texas, USA.
A critical step in the successful fabrication of coated conductors on metal substrates is to produce cube texture substrates using the RABiTS approach. Nickel has been used as a substrate for high-current coated YBa2Cu3Ox superconductors due to the relative ease in achieving sharp cube texture as well as chemical compatibility. High purity nickel (99.995%) samples were rolled to large deformation and annealed in 5% H2-95% Ar atmosphere at 700ore stabl C-1100YBCO film C for various times. The cube texture was promoted by recrystallization after cold rolling. The effects of deformation reduction per pass, amount of deformation, and annealing temperature and time on the recrystallization process were investigated using XRD and EBSD techniques. These parameters have been optimized to obtain the cube texture {100}<001>. The sharpest cube texture (>80% of grains within 7° and >97% within 10° cube textured) was obtained for nickel cold rolled by 2% reduction per pass and annealed at 1000° C for 90 minutes.
35.
Zhou, Y., K. T. Aust, et al. (2001). "Effects of grain boundary structure on carbide precipitation in 304L stainless steel." Scripta Materialia 45(No. 1): 49-54.
36.
Zhu, H., M. Mao, et al. (2005). "Measurement and analysis of microtexture in CVD free standing diamond films by EBSD." Chinese Journal of Stereology and Image Analysis 10(4): 229-232.
The microtextures and twins in the flank of CVD free standing diamond films were measured and analyzed by electron backscatter diffraction, and the fraction of the material with {100}, {110}, {111}, {122}, {447}, {148} growth direction textures were followed during the growth process. It was shown that the formation of {100}, {110}, and {111} textures was prevented by improper temperature control, and that {122}, {447}, {148} textures were formed as the result of twinning.
37.
Zhu, K. Y., D. Chaubet, et al. (2004). Microstructure and Texture Evolution during Static Recrystallization of Zr-2Hf Alloy. Second Joint International Conference on Recrystallization and Grain Growth, ReX & GG2, SF2M, Annecy, France, Trans Tech Publications Ltd.
The recrystallization of a Zr-2Hf alloy sheet deformed by plane strain compression at room temperature and then heat treated in the temperature range 500-650°C is studied. The microstructure, local and global crystallographic textures are investigated by EBSD and X-ray techniques. The as-deformed condition exhibits a heterogeneous microstructure composed of highly and less deformed zones, the EBSD indexing of the latter ones being more reliable. The as-deformed condition displays a (0001) <1010> crystallographic texture. The evolution of the microstructure during recrystallization very much depends on the amount of local deformation. Recrystallization begins in highly deformed zones, new grains having two variants of texture components, {0001} <1010> and {0001} <1120>. Some change of preferred orientations concomitant with grain growth at 600 and 650°C has been observed with a decrease in the {0001} <1010> component and an increase in the {0001} <1120> component.
38.
Zhu, K. Y., D. Chaubet, et al. (2005). "A study of recovery and primary recrystallization mechanisms in a Zr–2Hf alloy." Acta Materialia 53(19): 5131-5140.
The recrystallization of a Zr-2Hf alloy sheet deformed by plane strain compression at room temperature and then annealed at selected temperatures has been studied. The evolution of microstructure and crystallographic texture is investigated by in situ high voltage electron microscopy (HVEM), electron back-scattered diffraction (EBSD) and X-ray techniques. The deformed condition shows a heterogeneous microstructure, composed of highly and less deformed zones, and displays a main "tilted" {0001} (1010) texture component. The in situ HVEM examinations provide direct experimental evidence of microstructure evolution mechanisms during early stages of recrystallization: (1) rearrangement of dislocation cells into subgrains, (2) formation of nuclei through growth or coalescence of subgrains, (3) growth of nuclei by high angle boundary migration. EBSD and X-ray show that there is little change of the global crystallographic texture during these stages. With increasing annealing temperature or time, the new grains display two texture components, {0001}(1010) and {0001}(1120), the first of which disappears during grain growth.
39.
Zhu, Q., B. P. Wynne, et al. (2002). Texture Evolution of AA5052 during Monotonic and Reversed Hot Deformation and Subsequent Recrystallization. ICOTOM 13, Seoul, Korea, Trans Tech Publications Inc.
During industrial thermomechanical processing such as forging, rolling and extrusion, local regions within the stock undergo different strain paths. A significant effect of a change in strain path on microstructural evolution and subsequent recrystallisation behaviour has been observed previously for several texture free AL-Mg alloys under conditions of hot deformation in tension/compression. The mechanism of the effect is related to the evolution of geometrically necessary dislocations including the evolution of microbands, which are heterogeneously distributed in deforming materials and depend on the orientation of grains. This work is currently being extended to texture evolution during continuous and reversed deformation. The combined effects of strain path on dislocation substructures and on deformation texture determine the subsequent recrystallisation behaviour and recrystallisation texture, which in turn dominate deep drawing properties of sheet. The present paper shows the effect of a change in strain path on the evolution of texture during either simple shear or axisymmetric deformation of AA5052 and during annealing of the deformed materials. The experimental alloy has initial Goss and Cube texture components. The simple shear was carried out in a reversible torsion machine and axisymmetric deformation in a tension/compression-testing machine. Texture was examined using both an X-ray texture goniometer and by electron backscattered diffraction (EBSD) in a scanning electron microscope. The results show that the evolution of texture is different during monotonic and reversed shear deformation. After annealing to partially recrystallise, the difference of orientation distribution becomes more significant than in the specimens deformed in torsion. After annealing for a short time, where no recrystallisation can be found, the texture components are different from the partially recrystalllised specimens.
40.
Zhu, X. B., L. Chen, et al. (2004). "Effect of seed layers on the preparation of SrTiO3 buffer layers on Ni tapes via sol–gel method." Physica C 415(1-2): 57-61.
SrTiO3 (STO) buffer layers with different STO seed layers on Ni (2 0 0) substrates are fabricated using the spinning coating technique. It is found that the seed layers can remarkably affect the orientation of the subsequent STO precursor layer and the relationship between the orientation of the STO layer and the seed layer is discussed.
41.
Zhu, X. J., M. J. Tan, et al. (2005). "Enhanced superplasticity in commercially pure titanium alloy." Scripta Materialia 52(7): 651-655.
The superplasticity of commercially pure titanium alloy at high temperature was studied and the dynamic recrystallization phenomenon of the alloy was investigated by using electron back scattered diffraction. A two-step deformation method was used to increase the ductility of the alloy from 188% to 243%.
42.
Zhu, Y. H. (2004). "General rule of phase decomposition in Zn-Al based alloys (II) - On effects of external stresses on phase transformation." Materials Transactions 45(11): 3083-3097.
Microstructural changes and phase transformation of Zn-Al based alloys (ZA alloys) were systematically investigated during various thermal and thermo-mechanical processes using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro-analysis (EMPA), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and differential scanning calorimeter (DSC) etc. techniques. Phase decompositions of the alloys were studied under various thermal and thermo-mechanical circumstances. General rule of phase decomposition (II) (On effects of external stresses on phase transformation) was summarized with explanations from point view of Gibbs free energy.
43.
Zhu, Y. H., W. B. Lee, et al. (2001). "EBSD of Zn-rich phases in Zn-Al-based alloys." Materials Characterization 46(No. 1): 19-23.
Based on microstructure characterization, electron back-scatter Kikuchi diffraction (EBSD) methodology was used on a multi-phase alloy ZnAl4Cu11 (in wt.%). Electron back-scatter Kikuchi diffraction patterns (EBSDPs) were produced from the bulk Zn–Al-based alloy specimen using solely mechanical polishing instead of mechanical and electro-polishing. Both EBSDs of the Zn-rich hexagonal close-packed structure (hcp) phases of and were distinguished for the first time using pre-determined lattice parameters of these phases as the computer database for the multi-phase alloy. These two procedures were practical developments of EBSD technology in the study of crystalline orientation and phase identification.
44.
Zhu, Y. H., W. B. Lee, et al. (2003). "Aging characteristics of cast Zn-Al based alloy (ZnAl7Cu3)." Journal of Materials Science 38(9): 1945-1952.
Microstructure and ageing characteristics of a cast Zn-Al based alloy (ZnAl7Cu3) were studied using X-ray diffraction, electron scanning microscopy and back-scattered diffraction techniques. Two stages of phase transformation, i.e., decomposition of zinc rich eta phase and four phase transformation, alpha + epsilon -> T' + eta, were detected during ageing at 150 deg C. Electron back-scattered diffraction technique was applied in distinguishing both zinc rich eta and epsilon phases.
45.
Zhu, Y. H., W. B. Lee, et al. (2003). "Use of EBSD to study stress induced microstructural changes in Zn-Al based alloy." Materials Science and Engineering A 348(1-2): 6-14.
Tensile stress induced microstructural changes in an eutectoid Zn-Al based alloy were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) techniques. Both Zn-rich eta 'T and epsilon phases were identified by EBSD using predetermined lattice parameters of the phases. It was found that tensile deformation resulted in decomposition of the Zn-rich eta 'T and epsilon phases in the furnace cooled (FC) eutectoid Zn-Al based alloy. With increasing strain, the decomposition of the eta 'T and epsilon phases developed in the high stress concentrated neck zone and the rupture part of the FC-tensile deformed specimen. The measured preferred crystal orientations of the Zn-rich phases in the FC-tensile deformed Zn-Al alloy were in a good agreement with previous XRD investigation.
46.
Ziegler, A., G. H. Campbell, et al. (2003). Effects of grain boundary constraint on the constitutive response of tantalum bicrystals. Multiscale Phenomena in Materials - Experiments and Modeling Related to Mechanical Behavior. Symposium, San Francisco, CA, USA, Mater. Res. Soc.
The role of grain boundary constraint in strain localization, slip system activation, slip transmission, and the concomitant constitutive response was examined performing a series of uniaxial compression tests on tantalum bicrystals. Tantalum single crystals were diffusion bonded to form a (011) twist boundary and compressed along the Ý011¨ direction. The resulting three-dimensional deformation was analyzed via volume reconstruction. With this technique, both the effective states of stress and strain over the cross-sectional area could be measured as a function of distance from the twist boundary, revealing a highly constrained grain boundary region. Post-test metallurgical characterization was performed using Electron Back-Scattered-Diffraction (EBSD) maps. The results, a spatial distribution of slip patterning and mapping of crystal rotation around the twist-boundary, were analyzed and compared to the known behavior of the individual single crystals. A rather large area near the grain boundary revealed no crystal rotation. Instead, patterns of alternating crystal rotation similar to single crystal experiments were found to be some distance away (1mm) from the immediate grain boundary region, indicating the large length scale of the rotation free region.
47.
Zimmermann, F. and M. Humbert (2002). "Determination of the habit plane characteristics in the β–α' phase transformation induced by stress in Ti–5Al–2Sn–4Zr–
4Mo–2Cr–1Fe." Acta Materialia 50: 1735-1740.
The characteristics of the habit planes of the α' orthorhombic martensite plates, induced by stress within a commercial sheet of Ti–5Al–2Sn–4Zr–4Mo–2Cr–1Fe have been investigated. First, the orientations of several grains in BCC phase which presented at least one α orthorhombic martensite plate, were determined by EBSD. The Miller indexes of habit planes within a parent grain were deduced from the intersection lines of the martensite plates on two perpendicular sides of the sample and from the orientation of the parent grain. These data are compared to the characteristics of the habit planes, calculated from the phenomenological theory of the martensitic transformation proposed by Wechsler, Liebermann and Read. The different results and their dispersions are analysed in this contribution.
48.
Zondy, J. J. (1998). "The effects of focusing in type-I and type-II difference-frequency generations." Optics Communications 149(1-3): 181-206.
Beam aperture functions are derived for type-I and type-II difference-frequency generations using focused TEM00 Gaussian beams. The effects of walk-off, absorption, focusing and beam waist location are included in the analysis performed under the undepleted input wave approximation, using a Green's function approach. General expressions for the focusing h functions are given for arbitrary values of the input seed-wave confocal parameters, together with their optimized hm(B, mu) values as a function of the walk-off and degeneracy parameters (B, mu). The criterion of equal confocal parameters (ECP) is found to be optimal only for non-critical phase-matching. For critical phase-matching, unequal confocal parameters (UCP) generally optimize the efficiency. The theory is illustrated with relevant performance comparisons between the various type-I and type-IT DFG couplings using KTP and AgGaS2. (53 References).
49.
Zschech, E., W. Blum, et al. (2001). "Effect of Copper Line Geometry and Process Parameters on Interconnect Microstructure and Degradation Processes." Zeitschrift fur Metallkunde 92(7): 803-809.
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