Random Texture Research Articles

Study on Microstructure and Mechanical Property in Mg-Gd-Y Alloy by Secondary Extrusion Process

Extruded Mg-Gd-Y alloy tubes were obtained by using cast ingot and extruded bar billets. Microstructure and mechanical properties were also studied with two different cooling methods: air cooling and water cooling. The result shows that by using an extruded bar as billet extruded tubes achieves higher elongation comparing to using cast ingots due to favored texture for the activation of basal slip. Using the water-cooling method, extruded tubes achieve a higher yield strength compared to the air cooling method due to their fine grain size. Using cast ingot billets and the water-cooling method, the elongation is only 6% due to large unrecrystallized grains caused by inhomogeneous deformation and unfavored texture for the activation of basal slip. Using the extruded bar billet and the water-cooling method, the tube has uniformed small grains and much more randomized texture caused by the inhibition of preferred grain growth process. The highest texture intensity is only 1.852 in this kind of tube. Both high yield strength (195.3 MPa) and high elongation (23.9%) are achieved in this tube.

Grain Structure Evolution and Mechanical Properties of Multi-Channel Spiral Twist Extruded AA5083

This study presents a comprehensive evaluation of the effects of multi-channel spiral twist extrusion (MCSTE) processing on the mechanical properties and structural evolution of AA5083. The structural evolution and texture developed were mapped by electron backscatter diffraction (EBSD) for three successive passes and compared with an as-annealed plate. An evaluation of the hardness and tensile properties was presented and correlated with the EBSD findings. The displayed EBSD results revealed that grain refinement was strongly associated with the presence of a high density of low-angle grain boundaries (LAGBs) after one pass, which developed into fine grains of less than 20 μm and high-angle grain boundaries (HAGBs) after three MCSTE passes. The three pass processing led to a 65% reduction in grain size. This reduction in grain size was coupled with an enhancement in the hardness and tensile properties. Additionally, the crystallographic texture study represented a slightly random texture due to the presence of intermetallic particles in AA5083. This study demonstrates the efficacy of MCSTE as a grain refinement tool.

Amination of ether-linked polymers via the application of Ullmann-coupling reaction: synthesis, characterization, porosity, and thermal stability evaluation

In this report, an open-chain ether-linked polymer (PE-AF) has been prepared via one-step co-condensation polymerization of 1,4-dibromo-2,5-difluorobenzene with bisphenol AF. The new polymer has shown a good solubility in non-polar solvents, good thermal stability (up to 300 °C), high char residue with a limiting oxygen index (LOI) of 33.5, surface morphology with random fluffy-like texture, and a non-porosity nature with a surface area (SA) of 35 m2g−1. Tailoring these properties has been achieved by considering post-modification on the Bromo-sites of the polymer backbone. The post-modification was attained by applying Ullmann-coupling reaction of the Bromo-sites of PE-AF and aromatic diamines in presence of a catalytic amount of copper iodide. Upon inclusion of the aromatic diamines within the polymer’s backbone, the new polymers have depicted aggregated surface morphology (e.g. spherical particles ca. 0.3–0.1 µm), pronounced porosity nature (SA up to 354 m2g−1), varied range of pore size distribution, and higher thermal stability with lower char residue contents when compared with PE-AF. The successful production of the polymers was confirmed by (C, H, O, and N) elemental analysis, solid-state 13C-NMR, and infrared (IR) spectroscopy. The application of Ullmann-coupling raises the opportunity to create cavities and pores within the polymer’s framework. Though this modification lowered the LOI of the polymers and their flame-retardant tendency, it enhanced their opportunity for gas capture and separation applications.

The effect of heat treatments on mechanical properties of M789 steel fabricated by laser powder bed fusion

The microstructural evolution during the aging heat treatment of a newly developed steel (designed to be employed in the laser powder bed fusion), known as M789, was evaluated. The electron-backscatter diffraction (EBSD) analysis suggests that the as-printed sample contains a fully martensitic phase with random crystallographic texture. The samples were then solutionized at 1000 °C for 1 h, followed by aging at a temperature range of 400–600 °C and holding times from 40 to 120 min. The maximum hardness and tensile strength were achieved at aging temperatures of 450 °C and 500 °C for 2 h, with the latter temperature generated the highest amount of Ni3Ti precipitates (η-phase) with no traces of reverted austenite. Then, the heat-treated sample underwent transmission electron microscopy (TEM) and atom probe tomography (APT) analyses, which revealed the nano-scale, plate-like and spherical precipitates with number densities of 1.11 × 1024 m−3 and 0.93 × 1024 m−3, respectively. These precipitates contributed to the increase in tensile strength, from 1019 MPa (as-printed) to 1798 MPa (heat-treated), a net increase of 779 MPa. As a consequence of enhanced strength, the elongation decreased from 16% to 9%. Generally, the results of all experiments are consistent with simulations; the errors were identified to be less than 5%.

A Random Forest and Current Fault Texture Feature–Based Method for Current Sensor Fault Diagnosis in Three-Phase PWM VSR

Three-phase PWM voltage-source rectifier (VSR) systems have been widely used in various energy conversion systems, where current sensors are the key component for state monitoring and system control. The current sensor faults may bring hidden danger or damage to the whole system; therefore, this paper proposed a random forest (RF) and current fault texture feature–based method for current sensor fault diagnosis in three-phase PWM VSR systems. First, the three-phase alternating currents (ACs) of the three-phase PWM VSR are collected to extract the current fault texture features, and no additional hardware sensors are needed to avoid causing additional unstable factors. Then, the current fault texture features are adopted to train the random forest current sensor fault detection and diagnosis (CSFDD) classifier, which is a data-driven CSFDD classifier. Finally, the effectiveness of the proposed method is verified by simulation experiments. The result shows that the current sensor faults can be detected and located successfully and that it can effectively provide fault locations for maintenance personnel to keep the stable operation of the whole system.

Microstructure and Tensile Properties Anisotropy of 7xxx Ultra-Thick Plate

The microstructure，texture distribution and tensile property of 7xxx ultra-thick plate was investigated by optical microscopy (OM), scanning electron microscopy (SEM), electron back scattering diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests. The results show that the microstructure, texture and tensile property were inhomogeneous along the thickness direction. A large number of sub-crystals remained on the surface of the thick plate and was accompanied by much recrystallization. Most of the structures were random texture, and the proportion of typical texture was low at the edge. For the center layer, there were also a lot of recrystallized grains and typical deformed texture along the β-fiber (Brass, S, and Copper) was observed. The 1/4 layer of the plate is a transition one, and had the lowest recrystallized fraction. From surface to center, precipitation phases within grains and grain boundaries gradually coarsen, mechanical properties reduced. At the same thickness, the tensile property showed appreciable anisotropy, the L direction was the highest and the S direction was the lowest.

Microstructure and Texture Development in Thermomechanically Processed Leaded Brass

Leaded brass alloys with high zinc content are classified as dual-phase (α-β′) brass alloys. For these alloys, α-β′ phase transformation induced by thermomechanical processing (TMP) is expected to play a significant role not only in the formation of α and β′ phases and uniformity of lead particles but also in the development of Σ3 boundaries and their variants in the α phase. To assess such impact, the current study has employed two TMP schemes, with each scheme consisting of four cycles of compression and annealing. Samples of the first scheme (TMP-1) were annealed at 670 °C to promote phase transformation from α to β′, as compared to the second scheme (TMP-2) samples annealed at 525 °C. Microstructure examination indicated that TMP-1 scheme fostered a remarkable growth in the area fraction of β′ phase, accompanied by grain coarsening of α and β′ phases. This resulted in the isolation of α grains and less interaction of Σ3 boundaries at trip junctions, and therefore, a reduction in the fraction of Σ3 boundaries occurred in the α phase. On the other hand, the TMP-2 scheme successfully enhanced cluster formation of α grains, enabling further generation of Σ3 boundaries via strain-induced boundary migration mechanism and ultimately leading to breakup of the random boundary network. In addition, the two schemes resulted in limited coarsening of lead particles. Most lead particles were located at the α-βʹ interfaces, which suppressed grain boundary migration via the particle-dragging effect. For both TMP schemes, the initial texture of tension fibers was largely preserved after four cycles for both α and βʹ phases. Nevertheless, the TMP-2 scheme produced texture randomization of the α phase due to increasing the fraction of Σ3 boundaries.

A system for identifying an anti-counterfeiting pattern based on the statistical difference in key image regions

An important aspect of identifying whether items are likely to be forged or infringe upon a copyright is the use of an anti-counterfeiting pattern because it can help in determining and detecting forged anti-counterfeiting labels and patterns. At present, most anti-counterfeiting systems require special materials or large samples of images for training. Once they are geometrically attacked or forged by printing and scanning, they will be completely invalid. Therefore, this paper proposes an anti-counterfeiting system that uses a single corresponding feature difference sequence of the key regions for statistical analysis. The aim of our technology is to use the inks to generate random subtle texture patterns, and construct a supervised and guided segmentation algorithm and bone width transformation algorithm to locate the key regions of the sample images, which is used to identify the authenticity of the inspected product. The experiment shows that the system not only has high anti-counterfeiting performance and good robustness but also provides a convenient and practical idea for anti-counterfeiting technology.

Serrated flow behavior and microstructure evolution of Inconel 625 superalloy during plane-strain compression with different strain rates

Strain rate played an important role in the forming process of metal and alloy. In the present work, the effect of strain rate on deformation behavior and microstructure evolution of thermal-rolled Inconel 625 superalloy were systematically investigated by plane-strain compression (PSC) test at 1000 °C, and the strain rate range changed from 1 × 10−3 s−1 to 5 s−1. Obvious serrations occurred in strain rate range of 5 s−1 - 0.05 s−1 and transformed from type A to type A+B, and type B with decreasing of strain rate. Microscopic observations from transmission electron microscopy (TEM) indicated that type A and type B serration were related to slip bands nucleation-propagation, and carbon atoms-dislocations interaction, respectively. Electron backscatter diffraction (EBSD) technique and TEM were used to study the dynamic recrystallization (DRX) behavior during PSC. As the strain rates were greater than 5 s−1, DRX process was accelerated because of high deformed stored energy and adiabatic heating. This is undoubtedly a meaningful find to refine grain size and improve thermal processing efficiency. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) have been confirmed to occur simultaneously during the deformation process, but CDRX played a minor role in DRX nucleation. Texture evolution characteristics were also related to strain rate. Nearly random texture distribution was obtained as the strain rate above 0.5 s−1. Obvious Cu, E, S and Cube textures appeared in the strain rate range of 0.1 s−1–10−2 s−1. Grain orientations showed random distribution at the strain rate of 10−3 s−1. Moreover,<001> direction should be considered as preferred crystallographic orientations to recrystallization nucleation.

Microstructure, texture, and mechanical properties of the extruded and multi-directionally forged Mg–xGd alloys

The microstructural and textural evolutions as well as room-temperature mechanical properties of three binary Mg–Gd alloys with 1, 2, and 3 wt% of Gd were studied in the as-extruded condition and after two, four, and six passes of multi-directional forging (MDF). Microstructural observations of the extruded samples were indicative of partial dynamic recrystallization resulting in bimodal grain structures comprised of elongated un-recrystallized patches and fine recrystallized grains. After six passes of the MDF process, the fraction of the un-recrystallized regions decreased because of dynamic recrystallization, and thus, relatively uniform microstructures were achieved in all alloys. The greater fraction of the un-recrystallized patches and the finer grains in the recrystallized regions of the Mg–3Gd alloy confirmed the more pronounced retardation of recrystallization via solute drag mechanism at the higher Gd concentrations. Evaluation of crystallographic texture revealed that by applying the MDF process, the conventional fiber texture of the extruded condition was replaced with a new randomized texture, in which the basal planes had a tendency to rotate at angles of lower than 90° to the transverse direction. Mechanical properties were evaluated using shear punch testing (SPT) and the results showed that with increasing the number of MDF passes in each alloy, the achieved finer grain structure was responsible for improving the shear strength. In addition, increasing the Gd content of the alloys resulted in finer grain size, more solute atoms, and higher fraction of Mg 5 Gd second phase particles, all of which led to the enhancement in shear strength.

Microstructure and Crystallographic Texture of Laser Additive Manufactured Nickel-Based Superalloys with Different Scanning Strategies

Control of solidification structure and crystallographic texture during metal additive manufacturing is a challenging work which attracts the increasing interest of researchers. In the present work, two kinds of scanning strategies (i.e., single-directional scanning (SDS) and cross-directional scanning (CDS) were used to control the solidification structure and crystallographic texture during quasi-continuous-wave laser additive manufacturing (QCW-LAM) of Inconel 718. The results show that the solidification structure and texture are strongly dependent on scanning strategies. The SDS develops a typical fiber texture with unidirectional columnar grains, whereas the CDS develops a more random texture with a mixture of unidirectional and multidirectional grains. In addition, the SDS promotes the continuously epitaxial growth of columnar dendrites and results in the linearly distributed Laves phase particles, while the CDS leads to the alternately distributed Laves phase particles with chain-like morphology and discrete morphology. The changed stacking features of molten-pool boundary and the switched heat flow direction caused by different scanning strategies plays a crucial role on the epitaxial growth of dendrites and the final solidification structure of the fabricated parts.

Role of bimodal-grained structure with random texture on mechanical and corrosion properties of a Mg-Zn-Nd alloy

Fine grained ZN20 alloy was obtained by combining equal-channel angular pressing (ECAP) with extrusion. Microstructural observation showed an obvious grain refinement with an average grain size of 10 µm after ECAP. The original bimodal-grained structure composed of coarse grains with strong basal texture and fine grains with random texture was substituted by a new kind of bimodal-grained structure with finer grains and more random texture after 4 passes ECAP at 300 °C. The combination of grain refinement and texture weakening caused the ductility can be increased by 40% compared with the as-extruded alloy. Immersion test in simulated intestinal fluid revealed an improvement of corrosion resistance after ECAP. Grain refinement can stable the corrosion product layer and basal texture is more beneficial for the corrosion resistance than the non-basal texture.

Broadband angular color stability of dielectric thin film-coated pyramidal textured Si for photovoltaics

In this work we demonstrate the angular color stability of textured c-Si substrates colored by single layer thin film coatings of SiNx. These coatings show higher angular color stability on substrates with a random upright pyramidal surface texture compared to identical coatings on planar silicon substrates. Angle dependent reflectance measurements, supported by a modeling framework, display that the reflectance peaks originating from thin film interference of coated textured substrates only shift about 15 nm with an increasing angle of incidence from 10° to 80°, while the reflectance peaks of planar substrates with identical coatings shift about 120 nm at these angles. More specifically, reflectance peaks of planar substrates shift to shorter wavelengths, leading to a blue shift of the color appearance. The stable peak position of the textured samples is explained by a 2D representation of their surface texture and the primarily double interference interaction on it. While it is well known that a wide range of colors can be realized exhibiting low optical losses with thin film coatings, angular color stability was often not taken into account. However, for building integrated photovoltaics applications, a high angular color stability is desired, underlining the importance of using these textures. In most installed c-Si photovoltaics, similar substrate surface textures and dielectric thin film layers are already used. Therefore, this work envisions a route to facilitate large scale production of colored solar cells on textured c-Si substrates, colored by thin film SiNx layers, with minimized optical losses and improved angular color stability.

Influence of the textured pyramid size on the performance of silicon heterojunction solar cell

By adjusting the KOH/H2O texturing condition intendedly, different random pyramidal textures with the average pyramid size of 8 μm (large), 4 μm (medium) and 1.5 μm (small) were prepared on N type M2 monocrystalline silicon substrates for the fabrication of silicon heterojunction (SHJ) solar cell. It was evidenced that the pyramid morphology not only impacted the reflection of incident light and the heterojunction interface passivation quality but also affected the interface contact property between transparent conductive oxide (TCO) layer and Ag electrode. The texture with small pyramids presented the best anti-reflective and passivation performance due to the pyramidal size distribution uniformity, which brought the SHJ solar cell the highest short-circuit current density (JSC) and open-circuit voltage (VOC). However, the texture with small pyramids also led to the worst fill factor (FF). As a result, there was no obvious difference on the conversion efficiency for the textures with different pyramidal size. By characterizing the TCO/Ag contact, the FF reduction induced by the small pyramid texture could be attributed to the increased specific contact resistance of the TCO/Ag contact, which resulted from the fact that there were lots of voids between the TCO layer and Ag electrode, since Ag particles with a larger size than the small pyramids could not fill into the limited space between the adjacent pyramids. As a result, in order to realize the potential to enhance the SHJ solar cell conversion efficiency by adopting the texture with small pyramids, new Ag paste with smaller Ag particles should be adopted.

Origins of the enhanced broadband absorption in black silicon

Although black silicon is utilized in a wide range of applications due to its broadband spectral emission and absorption, the underlying electromagnetic mechanisms are not well explored. In this study, the underlying phenomena that are responsible for these enhanced spectral features are investigated. The absorption spectra of the black silicon with random textures are analyzed, and the electromagnetic mechanisms that drive elevated absorption are explored. Our findings reveal that two separate electromagnetic phenomena occur in the textures, effective wavelength matching and waveguide modes. Detailed analysis reveals that the occurrence condition of those phenomena is highly dependent on the dimensions of the textures in the transverse direction. The effect of the texture dimensions and doping concentration both on absorption characteristics and physical phenomena is analyzed in detail. The findings of this study explain the absorption mechanisms of black silicon observed in experimental studies, which can lead to designer materials with rough surfaces for the desired spectral emissivity.

On intergranular mechanical interactions and the theory of deformation crystallography of metals

The equilibrium of intergranular stress and strain can be realized simultaneously, whereas five independent slip systems of the Taylor principle and the criterion of minimal internal work are unnecessary. In fact, the Taylor principle applied in current theories is incorrect both in practice and theory, in which the activation mechanism of plastic deformation systems must violate the Schmid’s law and deviate from the elastic-plastic characteristics of deformed matrix. The intergranular reaction stress (RS) during deformation can be calculated according to Hooke’s law and elastic limit without additional subjective presupposition, therefore the RS theory is established intuitively. Under the combination of the RS (the intergranular elastic effect) and the external loading the slips penetrating grains are activated and produce deformation texture, but certain non-penetrating slips near grain boundaries will become active (the intergranular plastic effect) and produce some random texture when a RS reaches the yield strength of grains. The RS theory is simple, intuitive and reasonable, based on which the texture simulation can well reproduce the texture formation of various metals under different external loadings and under different crystallographic mechanisms.

Textured stainless steel foil as efficient rear reflector for flexible black silicon

This paper reports textured SS foil as an efficient rear reflector for flexible b-Si. Wafer thinning by concentrated potassium hydroxide (KOH) solution followed by metal-assisted chemical etching (MACE) are used to fabricate the flexible b-Si with 67 μm thickness. After the MACE process, the b-Si exhibit nanowires (NWs) with average diameter of 100 nm and height of 1.25 µm. To texture the stainless steel (SS) foil, wet chemical etching involving hydrofluoric (HF) acid (49%) is used at room temperature for different durations; from 10 to 30 min. When increasing the etching time of the SS foil, the SS foil exhibits formation of random textures with the roughest morphology after being etched for 20 min. At the same etching time, the SS foil also shows the highest root mean square (RMS) surface roughness and peak texture angle with a broad angle distribution. With the textured SS foil, the flexible b-Si demonstrates absorption enhancement of 1.27 at wavelength of 1075 nm due to the enhanced light scattering at the b-Si/textured SS interface.

Interactive Design of Random Aesthetic Abstract Textures by Composition Principles

Abstract The automatic synthesis of abstract textures is, to some extent, feasible. As evidenced by abstract art theoreticians, one can think of an abstract picture as a tree of elementary shapes interacting according to a short list of compositional laws such as occlusion, exclusion and bordering, and by rendering rules such as transparency, tessellation and color selection. Randomizing the shape generator and the composition and rendering laws yields an algorithm generating random abstract textures. We have designed a user-friendly online tool that implements this algorithm.

Effects of ausforming temperature on carbide-free bainite transformation and its correlation to the transformation plasticity strain in a medium C- Si-rich steel

Ausforming treatments at different temperatures were applied to a medium CSi rich carbide free bainitic steel, and the role of transformation plasticity on the evolution of the microstructure is discussed. Three ausforming temperatures were selected prior to isothermal bainite transformation at 325 °C. Deformation was applied above the bainite start temperature, BS, (600 °C), below BS (400 °C), and at the isothermal transformation temperature (325 °C). A combination of high-resolution dilatometry, XRD, SEM, and EBSD was used to investigate phase changes, microstructure evolution, and variant selections for the different ausforming conditions. The results indicated that the transformation rate was enhanced for all deformation conditions compared with the pure isothermal condition. Ausforming above BS did not modify the morphology of the carbide free microstructure, while ausforming below BS led to an asymmetrical morphology in the specimen. The alignment of the bainite plates can be at a random or a specific angle, depending on the supercooled austenite condition prior to the bainitic transformation. The thickness of the bainitic ferrite plates was refined to about 100 nm for the ausforming cycle at 325 °C resulting in a hardness of values of 540 HV. Transformation plasticity strains increased with increasing bainite transformation and were more intense with increasing microstructure alignment at the two lower ausforming temperatures. Texture studies revealed that both pure isothermal and ausforming at temperatures above BS resulted in an almost random texture, while a strong texture was obtained when ausforming below BS, a which was attributed to variant selection.

Review: Magnesium Sheet Alloy Development for Room Temperature Forming

Sheet metal forming operations in the automotive industry, including stamping, flanging, bending, hemming and trimming, are dominantly done at room temperature (RT). Unfortunately, the poor RT formability of magnesium due to its hexagonal close-packed structure and generally strong texture has limited the use of these processes in high-volume automotive production. However, the formability of magnesium can be improved via fine grain structure and random texture to enable some RT forming operations. This paper presents the latest magnesium alloy development and evaluation by the United States Automotive Materials Partnership (USAMP) in collaboration with its university partners. A new sheet alloy developed in a recent USAMP project, ZAXME11100 (USAMP Alloy 2 Plus), offers excellent ductility (31% tensile elongation) and RT formability (7.8 mm Erichsen index) in a solution-treated condition (T4), and a high yield strength (270 MPa) upon post-forming aging treatment (T6), promising RT forming for automotive applications.