Showing papers on "Texture (crystalline) published in 2014"

Effect of the build orientation on the mechanical properties and fracture modes of SLM Ti–6Al–4V

Abstract: Recent research on the additive manufacturing (AM) of Ti alloys has shown that the mechanical properties of the parts are affected by the characteristic microstructure that originates from the AM process. To understand the effect of the microstructure on the tensile properties, selective laser melted (SLM) Ti–6Al–4V samples built in three different orientations were tensile tested. The investigated samples were near fully dense, in two distinct conditions, as-built and stress relieved. It was found that the build orientation affects the tensile properties, and in particular the ductility of the samples. The mechanical anisotropy of the parts was discussed in relation to the crystallographic texture, phase composition and the predominant fracture mechanisms. Fractography and electron backscatter diffraction (EBSD) results indicate that the predominant fracture mechanism is intergranular fracture present along the grain boundaries and thus provide and explain the typical fracture surface features observed in fracture AM Ti–6Al–4V.

The effects of crystallographic orientation and strain of thin Hf0.5Zr0.5O2 film on its ferroelectricity

Abstract: To elucidate the origin of the formation of the ferroelectric phase in Hf0.5Zr0.5O2 films, the effects of film strain and crystallographic orientation on the properties were examined. Using a (111)-textured Pt bottom electrode, Hf0.5Zr0.5O2 films with a (111)-preferred texture inappropriate for transforming their phase from non-ferroelectric tetragonal to ferroelectric orthorhombic phase were deposited. In contrast, randomly oriented Hf0.5Zr0.5O2 films, grown on the TiN electrode, showed feasible ferroelectric properties due to their transformation to the ferroelectric orthorhombic phase. The origin of such transformation is the large in-plane tensile strain for the elongation of the c-axis of the tetragonal phase.

On the Texture Formation of Selective Laser Melted Ti-6Al-4V

Abstract: Selective laser melting (SLM) has been shown to be an attractive manufacturing route for the production of α/β titanium alloys. The relationship between the SLM process parameters and the microstructure of titanium alloys has been the object of several works, but the texture formation during the SLM process has yet to be understood. In the present study, the texture formation of Ti-6Al-4V components was investigated in order to clarify which microstructural features can be tailored during the SLM process. The microstructural characterization of the as-built components was carried out using various microscopy techniques. Phase and texture analysis were carried out using backscattered electron imaging and diffraction. It was found that as-built components consist exclusively of α′ martensitic phase precipitated from prior β columnar grains. The texture of the prior β phase was reconstructed and discussed in relation to the used SLM process parameters. It was found that the β grain solidification is influenced by the laser scan strategy and that the β phase has a strong 〈100〉 texture along its grain growth direction. The α′ martensitic laths that originate from the parent β grains precipitate according to the Burgers orientation relationship. It was observed that α′ laths clusters from the same β grain have a specific misorientation that minimizes the local shape strain. Texture inheritance across successive deposited layers was also observed and discussed in relation to various variant selection mechanisms.

Effect of Microtextured Surface Topography on the Wetting Behavior of Eutectic Gallium–Indium Alloys

Abstract: Liquid-embedded elastomer electronics have recently attracted much attention as key elements of highly deformable and "soft" electromechanical systems. Many of these fluid-elastomer composites utilize liquid metal alloys because of their high conductivities and inherent compliance. Understanding how these alloys interface with surfaces of various composition and texture is critical to the development of parallel processing technology, which is needed to create more complex and low-cost systems. In this work, we explore the wetting behaviors between droplets of gallium-indium alloys and thin metal films, with an emphasis on tin and indium substrates. We find that metallic droplets reactively wet thin metal foils, but the wettability of the foils may be tuned by the surface texture (produced by sputtering). The effects of both composition and texture of the substrate on wetting dynamics are quantified by measuring contact angle and droplet contact diameter as a function of time. Finally, we apply the Cassie-Baxter model to the sputtered and native substrates to gain insight into the behavior of liquid metals and the role of the oxide formation during interfacial processes.

Tailoring the grain structure of IN718 during selective electron beam melting

Abstract: Selective electron beam melting (SEBM) is an additive manufacturing method where complex parts are built from metal powders in layers of about 50 μm. SEBM works under vacuum conditions which results in a perfect protection of the metal alloy. The electron beam is used for heating (about 900 ∘ C building temperature) and selective melting. The high beam velocities allow innovative scanning strategies in order to adapt the local solidification conditions which determine the epitaxial solidification process of IN718. We show how scanning strategies can be used either to produce a columnar grain structure with a high texture in building direction or a complete texture-free fine grained structure. Numerical simulations of the selective melting process are applied to reveal the fundamental mechanisms responsible for the completely different grain structures. In addition the influence of the different grain structures on the mechanical properties of IN718 is briefly discussed.

Microstructure, texture evolution, mechanical properties and corrosion behavior of ECAP processed ZK60 magnesium alloy for biodegradable applications.

Abstract: Ultra-fine grained ZK60 Mg alloy was obtained by multi-pass equal-channel angular pressing at different temperatures of 250°C, 200°C and 150°C. Microstructural observations showed a significant grain refinement after ECAP, leading to an equiaxed and ultrafine grain (UFG) structure with average size of 600nm. The original extrusion fiber texture with planes oriented parallel to extrusion direction was gradually undermined during ECAP process and eventually it was substituted by a newly stronger texture component with considerably higher intensity, coinciding with ECAP shear plane. A combination of texture modification and grain refinement in UFG samples led to a marked reduction in mechanical asymmetric behavior compared to the as-received alloy, as well as adequate mechanical properties with about 100% improvement in elongation to failure while keeping relatively high tensile strength. Open circuit potential, potentiodynamic and weight loss measurements in a phosphate buffer solution electrolyte revealed an improved corrosion resistance of UFG alloy compared to the extruded one, stemming from a shift of corrosion regime from localized pitting in the as-received sample to a more uniform corrosion mode with reduced localized attack in ECAP processed alloy. Compression tests on immersed samples showed that the rate of loss of mechanical integrity in the UFG sample was lower than that in the as-received sample.

Rietveld texture analysis from synchrotron diffraction images. I. Calibration and basic analysis

Abstract: Synchrotron X-ray diffraction images are increasingly used to characterize not only structural and microstructural features of polycrystalline materials, but also crystal preferred orientation distributions. Diffraction data can be analyzed quantitatively and efficiently with the Rietveld method and here the detailed procedure is reported from the experiment to the calibration of the two-dimensional detector and full analysis of the sample. In particular, we emphasize the advantage of doing the calibration inside the Rietveld least-squares fitting instead of a preliminary graphical calibration. Then the procedure is described to quantify crystal preferred orientations with the Rietveld method implemented in software Materials Analysis Using Diffraction. The process is illustrated for a US nickel coin, a 75 at.% copper 25 at.% nickel alloy with face-centered cubic structure and a strong cube texture. © 2014 International Centre for Diffraction Data.

Spin Hall magnetoresistance at Pt/CoFe2O4 interfaces and texture effects

Abstract: We report magnetoresistance measurements on thin Pt bars grown on epitaxial (001) and (111) CoFe2O4 (CFO) ferrimagnetic insulating films. The results can be described in terms of the recently discovered spin Hall magnetoresistance (SMR). The magnitude of the SMR depends on the interface preparation conditions, being optimal when the Pt/CFO samples are prepared in situ, in a single process. The spin-mixing interface conductance, the key parameter governing SMR and other relevant spin-dependent phenomena, such as spin pumping or spin Seebeck effect, is found to be different depending on the crystallographic orientation of CFO, highlighting the role of the composition and density of magnetic ions at the interface on spin mixing.

Rietveld texture analysis from synchrotron diffraction images. II. Complex multiphase materials and diamond anvil cell experiments

Abstract: Synchrotron X-ray diffraction images are increasingly used to characterize crystallographic preferred orientation distributions (texture) of fine-grained polyphase materials. Diffraction images can be analyzed quantitatively with the Rietveld method as implemented in the software package Materials Analysis Using Diffraction. Here we describe the analysis procedure for diffraction images collected with high energy X-rays for a complex, multiphase shale, and for those collected in situ in diamond anvil cells at high pressure and anisotropic stress.

Twist-bend nematic liquid crystals in high magnetic fields

Abstract: We present magneto-optic measurements on two materials that form the recently discovered twist-bend nematic (N_{tb}) phase. This intriguing state of matter represents a fluid phase that is orientationally anisotropic in three directions and also exhibits translational order with periodicity several times larger than the molecular size. N_{tb} materials may also spontaneously form a visible, macroscopic stripe texture. We show that the optical stripe texture can be persistently inhibited by a magnetic field, and a 25T external magnetic field depresses the N-N_{tb} phase transition temperature by almost 1{∘}C. We propose a quantitative mechanism to account for this shift and suggest a Helfrich-Hurault-type mechanism for the optical stripe formation.

Anisotropic thermal conductivity of graphene wrinkles

Abstract: In this paper, the anisotropic thermal conductivity characteristics of graphene wrinkles are observed for the first time using a non-equilibrium molecular dynamics method. Our results reveal that the wrinkling level has little effect on the thermal conductivity along the wrinkling direction. However, the wrinkling level plays an important role in the reduction of thermal conductivity along the texture direction, which results from the contributions of increased bond length, von Mises stress, broadening of phonon modes and G-band redshift. These results indicate that graphene wrinkles can be a promising candidate to modulate thermal conductivity properties in nanoscale thermal managements and thermoelectric devices.

Microstructure and texture development during friction stir processing of Al–Mg alloy sheets with TiO2 nanoparticles

Abstract: Aluminum matrix nanocomposites were fabricated by friction stir processing of Al–Mg alloy sheets with pre-placed TiO 2 nanoparticles at a concentration of 2 to 6 vol%. Microstructural studies showed that solid state reactions between the metal matrix and TiO 2 particles caused in situ formation of MgO and Al 3 Ti nanophases with an average size ~50 nm. These nanophases were homogenously distributed in an ultra-fine grain structure (0.2–2 µm) of the base metal. The results of pole figures evaluation obtained by electron back scattered diffraction studies revealed that the random orientation of initial annealed sheet was changed to components near to shear and silver texture in the friction stir processed alloy without and with pre-placed powder, respectively. The concentration of TiO 2 particles affected the preferred texture orientation as the ceramic inclusion restricted the severe plastic deformation and dynamic recrystalization of the metal matrix. Hardness and tensile yield strength of the Al–Mg alloy sheet were also significantly improved by employing friction stir processing in the presence of TiO 2 nanoparticles (up to ~3.1 vol%). Fractographic studies showed a mixture of ductile–brittle fracture modes with an increase in the content of catastrophic manner at higher TiO 2 fractions.

Do the short helices exist in the nematic TB phase

Abstract: Dimeric compounds forming twist-bend nematic, Ntb, phase show unusual optical texture related to the formation of arrays of focal conic defects. Some of the focal conics show submicron internal structure with 8 nm periodicity, which is very close to that found in the crystalline phase of the material, suggesting surface freezing.

Effect of rolling reduction on microstructure, texture, mechanical properties and mechanical anisotropy of AZ31 magnesium alloys

Abstract: Mechanical properties of as-rolled magnesium alloy sheets show an obvious anisotropy during rolling. To get sheets with excellent performance and investigate the effect of microstructure, texture on mechanical properties and mechanical anisotropy, AZ31 magnesium alloy sheets with 4 mm in thickness were obtained by multi-pass hot rolling using different single pass rolling reductions. The texture evolution of the as-rolled AZ31 magnesium sheets was analyzed by the electron backscattered diffraction (EBSD) method. The Hall–Petch and Schmid law effect were discussed in detail on the basis of experiment. A revised form of Hall–Petch formula was proposed with the consideration of texture effect as σ s − t = ( 0.3 / m t ) ( σ 0 + k d − 1 / 2 ) . The mechanical properties were greatly enhanced by multi-pass hot rolling and the enhancement was attributed to both grain refinement and texture intensity. The results would provide useful guidance to design a rolling processing route for AZ31 Mg Alloys sheet.

Tribological Characteristics of (TiZrHfVNbTa)N Coatings Applied Using the Vacuum Arc Deposition Method

Abstract: The effect of the pressure of the nitrogen atmosphere during the formation of vacuum arc nitride coatings based on high entropy alloys of the Ti-Zr-Hf-V-Nb-Ta system on their structure, hardness, and tribotechnical characteristics is considered. It is shown that strong nitride-forming components lead to the dependence of the structural state and properties on the pressure of the nitrogen atmosphere during coating deposition. Deposition at a nitrogen pressure of 0.4 Pa results in the formation of a texture with the [111] axis when the applied bias potential is −70 V and when the bias potential is equal to −150 V the textural structure is biaxial ([111] and [110]) textures and high value of hardness of 51 GPa Along with that the highest value of wear resistance (under oxidizing-mechanical wear) is inherent to coatings formed under the pressure of nitrogen of 0.09 Pa. The strongest microdeformation of coating crystallites corresponds to this pressure.