Showing papers on "Texture (crystalline) published in 2013"

Highly Anisotropic Steel Processed by Selective Laser Melting

Abstract: For additive manufacturing of metals, selective laser melting can be employed. The microstructure evolution is directly influenced by processing parameters. Employing a high energy laser system, samples made from austenitic stainless steel were manufactured. The microstructure obtained is characterized by an extremely high degree of anisotropy featuring coarse elongated grains and a 〈001〉 texture alongside the build direction during processing. Eventually, the anisotropy of the microstructure drastically affects the monotonic properties of the current material.

Ice adhesion on lubricant-impregnated textured surfaces.

Abstract: Ice accretion is an important problem and passive approaches for reducing ice-adhesion are of great interest in various systems such as aircrafts, power lines, wind turbines, and oil platforms. Here, we study the ice-adhesion properties of lubricant-impregnated textured surfaces. Force measurements show ice adhesion strength on textured surfaces impregnated with thermodynamically stable lubricant films to be higher than that on surfaces with excess lubricant. Systematic ice-adhesion measurements indicate that the ice-adhesion strength is dependent on texture and decreases with increasing texture density. Direct cryogenic SEM imaging of the fractured ice surface and the interface between ice and lubricant-impregnated textured surface reveal stress concentrators and crack initiation sites that can increase with texture density and result in lowering adhesion strength. Thus, lubricant-impregnated surfaces have to be optimized to outperform state-of-the-art icephobic treatments.

Effects of processing on microstructure and mechanical properties of a titanium alloy (Ti–6Al–4V) fabricated using electron beam melting (EBM), Part 2: Energy input, orientation, and location

Abstract: Selective electron beam melting (EBM) is a layer-by-layer additive manufacturing technique that shows great promise for fabrication of medical devices and aerospace components. Before its potential can be fully realized, however, a comprehensive understanding of processing-microstructure-properties relationships is necessary. Titanium alloy (Ti–6Al–4V) parts were built in a newly developed, unique geometry to allow accurate investigation of the following intra-build processing parameters: energy input, orientation, and location. Microstructure evaluation (qualitative prior-β grain size, quantitative α lath thickness), tensile testing, and Vickers microhardness were performed for each specimen. For a wide range of energy input (speed factor 30–40), small differences in mechanical properties (2% change in ultimate tensile strength (UTS) and 3% change in yield strength (YS)) were measured. Vertically built parts were found to have no difference in UTS or YS compared to horizontally built parts, but the percent elongation at break (% EL) was 30% lower. The difference in % EL was attributed to a different orientation of the tensile axis for horizontal and vertical parts compared to the elongated prior-β grain and microstructural texture direction in EBM Ti–6Al–4V. Orientation within the x – y plane as well as location were found to have less than 3% effect on mechanical properties, and it is possible a second order effect of thermal mass contributed to these results.

Observation of a distinct surface molecular orientation in films of a high mobility conjugated polymer.

Abstract: The molecular orientation and microstructure of films of the high-mobility semiconducting polymer poly(N,N-bis-2-octyldodecylnaphthalene-1,4,5,8-bis-dicarboximide-2,6-diyl-alt-5,5-2,2-bithiophene) (P(NDI2OD-T2)) are probed using a combination of grazing-incidence wide-angle X-ray scattering (GIWAXS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy. In particular a novel approach is used whereby the bulk molecular orientation and surface molecular orientation are simultaneously measured on the same sample using NEXAFS spectroscopy in an angle-resolved transmission experiment. Furthermore, the acquisition of bulk-sensitive NEXAFS data enables a direct comparison of the information provided by GIWAXS and NEXAFS. By comparison of the bulk-sensitive and surface-sensitive NEXAFS data, a distinctly different molecular orientation is observed at the surface of the film compared to the bulk. While a more "face-on" orientation of the conjugated backbone is observed in the bulk of the film, consistent with the lamella orientation observed by GIWAXS, a more "edge-on" orientation is observed at the surface of the film with surface-sensitive NEXAFS spectroscopy. This distinct edge-on surface orientation explains the high in-plane mobility that is achieved in top-gate P(NDI2OD-T2) field-effect transistors (FETs), while the bulk face-on texture explains the high out-of-plane mobilities that are observed in time-of-flight and diode measurements. These results also stress that GIWAXS lacks the surface sensitivity required to probe the microstructure of the accumulation layer that supports charge transport in organic FETs and hence may not necessarily be appropriate for correlating film microstructure and FET charge transport.

Effects of cerium addition on the microstructure, mechanical properties and hot workability of ZK60 alloy

Abstract: The effects of cerium (Ce) addition on the microstructure and mechanical properties of ZK60 alloy were investigated using SEM, EBSD, and TEM and by performing tensile tests of indirect-extruded ZK60 alloys with 0.5, 1.0, and 1.5 wt% Ce contents. The variation of hot workability due to Ce addition was also investigated by establishing processing maps of these alloys. The results revealed that Ce addition had an obvious influence, reducing the average grain size and weakening the basal fiber texture of the as-extruded ZK60 alloys; these changes were attributed to the promotion of dynamic recrystallization (DRX) by particle stimulated nucleation (PSN) at Mg–Zn–Ce particles. The yield and tensile strengths were improved by the Ce addition, while the elongation was decreased due to the hard Mg–Zn–Ce particles. It was also found that the hot workability improves up to the addition of 1.0 wt% Ce and then deteriorates.

Evolution of microstructure, macrotexture and mechanical properties of commercially pure Ti during ECAP-conform processing and drawing

Abstract: Long-length ultrafine-grained (UFG) Ti rods are produced by equal-channel angular pressing via the conform scheme (ECAP-C) at 200 °C, which is followed by drawing at 200 °C. The evolution of microstructure, macrotexture, and mechanical properties (yield strength, ultimate tensile strength, failure stress, uniform elongation, elongation to failure) of pure Ti during this thermo-mechanical processing is studied. Special attention is also paid to the effect of microstructure on the mechanical behavior of the material after macrolocalization of plastic flow. The number of ECAP-C passes varies in the range of 1–10. The microstructure is more refined with increasing number of ECAP-C passes. Formation of homogeneous microstructure with a grain/subgrain size of 200 nm and its saturation after 6 ECAP-C passes are observed. Strength properties increase with increasing number of ECAP passes and saturate after 6 ECAP-C passes to a yield strength of 973 MPa, an ultimate tensile strength of 1035 MPa, and a true failure stress of 1400 MPa (from 625, 750, and 1150 MPa in the as-received condition). The true strain at failure failure decreases after ECAP-C processing. The reduction of area and true strain to failure values do not decrease after ECAP-C processing. The sample after 6 ECAP-C passes is subjected to drawing at 200¯C resulting in reduction of a grain/subgrain size to 150 nm, formation of (10 1 ¯ 0) fiber texture with respect to the rod axis, and further increase of the yield strength up to 1190 MPa, the ultimate tensile strength up to 1230 MPa and the true failure stress up to 1600 MPa. It is demonstrated that UFG CP Ti has low resistance to macrolocalization of plastic deformation and high resistance to crack formation after necking.

Structured color humidity indicator from reversible pitch tuning in self-assembled nanocrystalline cellulose films

Abstract: Iridescence is an example of structured color that is widespread in the biosphere, exhibited by multilayer inorganic thin films for optical filters, photonic crystals and other materials in which the periodic patterning of matter interacts with an electromagnetic field. Nanocrystalline cellulose (NCC) can be cast in the form of thick iridescent films whose color originates in the multi-domain chiral nematic texture created by self-assembly of the rigid rod crystallites. Scanning electron microscopy confirms the periodic layer structure that arises from the helical twist axis of the chiral nematic mesophase film. In effect, the film comprises multi-domain Bragg reflectors. On exposure to liquid water, and high relative humidity (RH), a reversible shift in the film iridescence from dry state blue-green to wet state red-orange is observed. This color change, which requires no pigment, is quantified by reflectance spectroscopy. The color transition is attributed to sorption of water that causes the pitch of the Bragg reflector to enlarge, and this leads to a red shift in the iridescence. The subsequent expansion of the film thickness was observed using polarized optical microscopy. The effect resembles molecular dopant and electric field induced pitch tuning along the helicoid axis in one-dimensional photonic crystal-like chiral nematic molecular systems. The color shift for a 40 μm thick NCC film is slow, occurring on timescale of 1–3 min. Thinner films change color in less than 2 s.

Twin polymerization at spherical hard templates: an approach to size-adjustable carbon hollow spheres with micro- or mesoporous shells.

Abstract: Kitset hollow spheres: The combination of twin polymerization with hard templates makes hollow carbon spheres (HCSs) with tailored properties easily accessible. The thickness and pore texture of the HCS shells and also the diameter of the spherical cavity can be varied. The application potential of synthesized HCS is substantiated by an excellent cycling stability of lithium-sulfur batteries.

Effect of long period stacking ordered phase on the microstructure, texture and mechanical properties of extruded Mg–Y–Zn alloy

Abstract: The effect of long period stacking ordered (LPSO) phase on the microstructure, texture and mechanical properties of extruded Mg-Y-Zn alloys with compositions of Mg98.5Y1Zn0.5, Mg95.5Y3Zn1.5 and Mg92.5Y5Zn2.5 (at%), was systematically investigated. The LPSO phases were aligned along the extrusion direction (ED) in the as-extruded Mg-Y-Zn alloys, and significantly enhanced the dynamic recrystallization (DRX) process during the hot extrusion. With the increase of LPSO phase, the degree of DRX process of Mg alloy was more completed, the growth of the DRXed grains resulted in the grain coarsening, and the following phenomena were also observed that the conventional basal fiber texture was remarkably weakened, a novel texture component of //ED appeared in the Mg alloys with higher volume fraction of LPSO phase. The microhardness and tensile yield stress (TYS) of Mg-Y-Zn alloy was improved by LPSO phase, but the ductility was degraded. The strengthening effect of LPSO phase was dominant over that from the grain refinement and texture. (c) 2012 Elsevier B.V. All rights reserved.

Hot deformation induced bulk nanostructuring of unidirectionally grown p-type (Bi,Sb)2Te3 thermoelectric materials

Abstract: Nanostructuring has proved effective in improving the figure of merit in the widely used Bi2Te3 based thermoelectric materials. In this work, a hot deformation induced in situ nanostructuring process is directly applied to the commercial unidirectionally grown p-type Bi0.5Sb1.5Te3 ingots to explore the possibility of commercial application of the “top down” nanostructuring approach, and the thermoelectric properties are investigated over a wide temperature range of 15 K to 520 K. In comparison to the commercial zone melted ingot and the hot pressed sample, it is found that the hot deformed samples exhibit much less texture and significantly reduced lattice thermal conductivity due to in situ formed nanostructures and defects. A high ZT of ∼1.3 is achieved near room temperature, ∼50% improvement compared to that of the zone melted ingot. The hot deformation process thus provides a promising top down approach to prepare high performance Bi2Te3 based thermoelectric materials in a way that is more readily incorporated into the existing procedure of device manufacturing.

Influence of substrate temperature on the structural, optical and electrical properties of CdS thin films deposited by thermal evaporation

Abstract: CdS thin films were deposited onto glass substrates at three different temperatures (20, 100 and 200 °C) by vacuum thermal evaporation at 10 −5 Torr using pure crystal as evaporated targets The effects of substrate temperature on structural, electrical and optical properties were studied Structural analysis using X-ray diffraction (XRD) and scanning electronic microscope (SEM) revealed that the films are polycrystalline in nature with a hexagonal wurtzite structure having (0 0 2) plane as the preferred orientation The crystalline size ( D ), dislocation density ( δ ), strain ( e ) and texture coefficient TC ( hkl ) were calculated All the films have high optical transmittance (>80%) in the visible range The optical band gap values are found to be in the range of (23–243 eV) and found to decrease with increase in substrate temperature DC electrical conductivity was carried out at room temperature indicating a very low electrical conductivity

α-Fe2O3 nanocolumns and nanorods fabricated by electron beam evaporation for visible light photocatalytic and antimicrobial applications.

Abstract: Both Fe2O3 thin films and nanorod arrays are deposited using electron beam evaporation through normal thin film deposition and oblique angle deposition (OAD) and are characterized structurally, optically, and photocatalytically. The morphologies of the thin films are found to be arrays of very thin and closely packed columnar structures, while the OAD films are well-aligned nanorod arrays. All films were determined to be in the hematite phase (α-Fe2O3), as confirmed by both structural and optical characterization. Texture measurements indicate that films have similar growth modes where the [110] direction aligns with the direction of material growth. Under visible light illumination, the thin film samples were more efficient at photocatalytically degrading methylene blue, while the nanorod arrays were more efficient at inactivating E. coli O157:H7. The size of the targeted agent and the different film morphologies result in different reactant/surface interactions, which is the main factor that determines ...

Hot deformation mechanism and microstructure evolution of a new near β titanium alloy

Abstract: Transmission Electron Microscope (TEM) and Electron Backscattered Diffraction (EBSD) are employed to explore the influence of deformation conditions on microstructure and the deformation mechanism of a new near β titanium alloy Ti-7333 after hot compression tests which at temperatures ranging from 770 to 970 °C and strain rates ranging from 0.001 to 10 s −1 . The results showed that the effect of deformation parameters on microstructure evolution is significantly. Both increasing the temperature and decreasing the strain rate seem to promote the dynamic recrystallization process. The mechanism is dominated by dynamic recovery, globularization and dynamic recrystallization. The globularization trend of α phase is more remarkable deformed at higher temperature and lower strain rate. And reverse, the lower temperature and higher strain rate are more favorable to α phase refinement. The fraction of low-angle grain boundaries in the deformation microstructure decreases with the increasing of temperature and decreasing of strain rate. It illustrates the low-angle grain boundaries would turn to high-angle grain boundaries during deformation. The expression of the size of recrystallized grains D r and parameter Z is obtained by regression analysis as ln D r =8.79964−0.33663ln Z . All the deformed samples present strong 〈001〉 and weak 〈111〉 fiber texture. With the increasing of temperature and decreasing of strain rate, the 〈001〉 texture strengthens gradually and 〈111〉 texture weakens gradually until extinction.

Effect of Li addition on the mechanical behavior and texture of the as-extruded AZ31 magnesium alloy

Abstract: Lithium alloying additions are verified to be an effective way to enhance the room temperature formability of magnesium. In this work, AZ31 (Mg–3 wt% Al–1 wt% Zn) alloys with different lithium additions (0–5 wt%) were melted and extruded to 2 mm thick sheets at 380 °C. The microstructure and texture evolution were investigated by optical microscopy, X-ray diffraction (XRD) and electronic backscattered diffraction (EBSD). Tensile tests along three directions were carried out at room temperature, to access the mechanical properties and anisotropy. It was found that the mechanical anisotropy of the as-extruded AZ31 alloy was modified remarkably with lithium additions and AZ31 alloy with 5% Li content was found to have the smallest planar anisotropy and enhanced elongation. Lithium additions also increased the rotation of basal poles in the transverse direction, which was attributed to decreased c / a ratio and refined recrystallized structure. The thickness reduction and width reduction during tensile test were also measured and discussed.

Giant energy density in [001]-textured Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 piezoelectric ceramics

Abstract: Pb(Zr,Ti)O3 (PZT) based compositions have been challenging to texture or grow in a single crystal form due to the incongruent melting point of ZrO2. Here we demonstrate the method for achieving 90% textured PZT-based ceramics and further show that it can provide highest known energy density in piezoelectric materials through enhancement of piezoelectric charge and voltage coefficients (d and g). Our method provides more than ∼5× increase in the ratio d(textured)/d(random). A giant magnitude of d·g coefficient with value of 59 000 × 10−15 m2 N−1 (comparable to that of the single crystal counterpart and 359% higher than that of the best commercial compositions) was obtained.

Microstructure and mechanical properties of MgZnY alloy sheet prepared by hot-rolling

Abstract: In this study, the microstructure and mechanical properties of MgZnY alloy sheets were investigated. Tensile tests at room temperature were performed along the rolling direction of Mg98Zn1Y1-, Mg96Zn2Y2-, and Mg94Zn3Y3- alloy sheets and their annealed states (773 K for 0.6 ks). These alloy sheets exhibited yield strengths of 261, 317, and 380 MPa, and elongations of 12, 10, and 6%, respectively. The yield strength of a MgZnY alloy sheet with Zn and Y contents greater than 2 at% was higher than 300 MPa. The microstructure observations suggested that the alloy sheet strength mainly resulted from (i) the formation of basal texture in the long period stacking ordered (LPSO) phase and (ii) the uniform dispersion of a fine Mg3Zn3Y2 phase. In the annealed state, the yield strength tended to decrease, while the elongation tended to increase. Large elongations of 20% or more were achieved in the Mg98Zn1Y1- and Mg96Zn2Y2 -alloy annealed sheets. The cold workability of the MgZnY alloy sheets and an AZ31-O sheet were evaluated, using a V-bending test at room temperature. Both Mg98Zn1Y1- and Mg96Zn2Y2- annealed sheets could be bent without cracking with a minimum bending radius per thickness of 3.3, which was less than that of the AZ31-O sheet. Texture randomization occurred in the MgZnY alloy annealed sheets owing to re-crystallization of the Mg phase, which was confirmed by electron backscattering diffraction (EBSD) analysis. Large elongations and good cold workability of the MgZnY annealed sheets are presumably attributed to an increase in the randomness of the Mg phase owing to re-crystallization. These results suggested that a Mg alloy sheet of high yield strength or good cold workability could be prepared by controlling the alloy composition and its microstructure in the MgZnY alloy system.

Effect of extrusion ratio on microstructure, texture and mechanical properties of indirectly extruded Mg–Zn–Ca alloy

Abstract: Indirect extrusion of as-cast Mg-5.25 Zn-0.6 Ca (wt%) alloy was performed at 300 degrees C with different extrusion ratios (ER, 20:1 and 10:1), and the microstructure, texture and tensile properties of the as-extruded alloys were investigated in the current study. With the increase of ER, the volume fraction of DRXed grains was remarkably increased, but the average DRXed grains size was almost unchanged. The basal texture weakening phenomenon occurred in the as-extruded alloy with higher ER, which resulted from the higher volume fraction of the DRXed grain. Intensive basal fiber texture was observed in the unDRXed grains, but the basal planes of the DRXed grains were inclined to ED from 0 degrees to 35 degrees. The ER had only little effect on the tensile properties of the as-extruded alloys; due to the similar strengthening effect from the unDRXed and DRXed grains, a competitive mechanism exists between the fine grain strengthening and texture weakening effect. (C) 2013 Elsevier B.V. All rights reserved.

Magnetostriction and magnetic texture to 100.75 Tesla in frustrated SrCu$_2$(BO$_3$)$_2$

Abstract: Strong geometrical frustration in magnets leads to exotic states such as spin liquids, spin supersolids, and complex magnetic textures. SrCu2(BO3)2, a spin-1/2 Heisenberg antiferromagnet in the archetypical Shastry–Sutherland lattice, exhibits a rich spectrum of magnetization plateaus and stripe-like magnetic textures in applied fields. The structure of these plateaus is still highly controversial due to the intrinsic complexity associated with frustration and competing length scales. We discover magnetic textures in SrCu2(BO3)2 via magnetostriction and magnetocaloric measurements in fields up to 100.75 T. In addition to observing low-field fine structure with unprecedented resolution, the data also reveal lattice responses at 73.6 T and at 82 T that we attribute, using a controlled density matrix renormalization group approach, to a unanticipated 2/5 plateau and to the long-predicted 1/2 plateau.

Flow softening, twinning and dynamic recrystallization in AZ31 magnesium

Abstract: The compression tests were carried out on AZ31 magnesium alloy samples at temperatures from 300 to 450 °C and strain rates of 0.03–0.3 s−1. The evolution of the microstructure and texture was followed and the volume fractions recrystallized were determined as a function of strain and temperature. The flow curves were analyzed using the double differentiation method and double minima were detected on all the curves. The first set of minima is shown to identify the critical strain for twinning, while the second set indicates the critical strain for the initiation of dynamic recrystallization. The texture analysis and EBSD results indicate that flow softening is mainly caused by the grain reorientations brought about by twinning. The remainder of the flow softening is associated with the volume fraction recrystallized. The microstructure analysis shows that the volume fraction recrystallized does not approach its asymptotic value of one even during steady state flow.