Formation Of Crystallographic Texture Research Articles

Regularities of crystallographic texture formation in EP648 alloy obtained by selective laser powder melting

Regularities of crystallographic texture formation in EP648 alloy obtained by selective laser powder melting

Solidification and crystallographic texture modeling of laser powder bed fusion Ti-6Al-4V using finite difference-monte carlo method

Laser powder bed fusion (LPBF) additive manufacturing makes near-net-shaped parts with reduced material cost and time, rising as a promising technology to fabricate Ti-6Al-4 V, a widely used titanium alloy in aerospace and medical industries. However, LPBF Ti-6Al-4 V parts produced with 67° rotation between layers, a scan strategy commonly used to reduce microstructure and property inhomogeneity, have varying grain morphologies and weak crystallographic textures that change depending on processing parameters. This study predicts LPBF Ti-6Al-4 V solidification at three energy levels using a finite difference-Monte Carlo method and validates the simulations with large-area electron backscatter diffraction (EBSD) scans. The developed model accurately shows that a 〈001〉 texture forms at low energy and a 〈111〉 texture occurs at higher energies parallel to the build direction but with a lower strength than the textures observed from EBSD. A validated and well-established method of combining spatial correlation and general spherical harmonics representation of texture is developed to calculate a difference score between simulations and experiments. The quantitative comparison enables effective fine-tuning of nucleation density (N0) input, which shows a nonlinear relationship with increasing energy level. Future improvements in texture prediction code and a more comprehensive study of N0 with different energy levels will further advance the optimization of LPBF Ti-6Al-4 V components. These developments contribute a novel understanding of crystallographic texture formation in LPBF Ti-6Al-4 V, the development of robust model validation and calibration pipeline methodologies, and provide a platform for mechanical property prediction and process parameter optimization.

In-situ synchrotron high energy X-ray diffraction study on the deformation mechanisms of D019-α2 phase during high-temperature compression in a TiAl alloy

The α2 phase with an ordered hexagonal structure has a strong mechanical anisotropy. The limited plasticity interacting with crystallographic texture formation undoubtedly complicate the deformation mechanisms of the α2 phase. Taking advantage of in-situ synchrotron high energy X-ray diffraction (HEXRD), this study unveils the origin of the α2 texture and its correlation with plastic deformation. Upon loading at 800 °C, the dislocation glide in the γ phase initiates at a stress of 370 MPa and that in the α2 phase at a stress of 670 MPa. Nevertheless, the texture evolution of the α2 phase sets in in parallel with that of the γ phase, and these textures are preliminarily established at a stress of 650 MPa. A main <11 2‾ 0> fiber texture with the c axis of the α2 unit cell aligned vertically to the compression axis has been unexpectedly evolved. This texture forms primarily via rigid body rotation and is correlated with glide and twin activation in the neighboring γ phase. The preferential orientation primarily favors double prismatic glide in α2 and in addition triggers the tensile twin activation. The grain rotation caused by the tensile twin slightly affects the α2 transverse texture evolution. The results unveil a complex interaction between the α2 phase deformability, texture evolution and the combined elastic-plastic deformation of the phases γ and α2 in TiAl alloys.

Evolution of Structure and Texture Formation in Thermomechanically Treated Ti-Zr-Nb Shape Memory Alloys

Biomedical Ti-22Nb-6Zr, Ti-18Zr-15Nb, and Ti-41Zr-12Nb (at.%) shape memory alloys were subjected to cold rolling (CR) and subsequent post-deformation annealing (PDA). The evolutions of phase and structure states, crystallographic texture, and crystallographic limit of recovery strain were studied using EBSD, TEM, and XRD analyses. The study found that CR (e = 1.5) and PDA at 800 °C for 30 min results in fine- and coarse-grained structures. Severe CR (e = 3.0) and PDA at 550 °C for 5 min results in a recrystallized, equiaxed, predominantly ultrafine-grained structure of the β-phase with a small amount of low-angle boundaries. Increasing the degree of CR from moderate (e = 0.3) to severe (e = 3.0) results in a favorable strong {111}β&lt;110&gt;β recrystallization texture. Alloys with low Zr content are more susceptible to this type of crystallographic texture formation during TMT, primarily due to a higher Nb content. The Ti-41Zr-12Nb alloy shows the highest crystallographic limit of recovery strain (εrmax ≈ 6%). The limit decreases to ≈5% (for Ti-18Zr-15Nb) and ≈3% (for Ti-22Nb-6Zr) when transitioning from high- to low-Zr alloys. The transition of Ti-Zr-Nb alloys from coarse-grained to ultrafine-grained structures of the β-phase and a decrease in grain size do not affect the crystallographic limit of recovery strain in the studied grain size ranges.

Microstructure and Crystallographic Texture Evolution of β-Solidifying γ-TiAl Alloy During Single- and Multi-track Exposure via Laser Powder Bed Fusion

The microstructural evolution and crystallographic texture formation of β-solidifying Ti-44Al-6Nb-1.2Cr alloy were identified under single- and multi-track exposures via laser powder bed fusion (L-PBF) for various process parameters. Under single-track exposure, the microstructure of the melt pool was divided into the band-like α2 phase in the melt pool boundary and β phase in the melt pool center. Numerical and thermodynamic simulations revealed that the underlying mechanism of phase separation was related to the variation in the cooling rate in the melt pool, whereas microsegregation induced a shift in the solidification path. Meanwhile, the crystallographic texture of the α2 phase region was identical to that of the substrate owing to the epitaxial growth of the β phase and subsequent α phase nucleation. In contrast, the β phase exhibited a ± 45° inclined <100> alignment in the melt pool, which was tilted to align along the build direction toward the center of the melt pool corresponding to the simulated thermal gradient direction. Furthermore, the narrow hatch space condition maintained the crystallographic texture to the subsequent scan, forming a continuous band-like α2 phase with a strong selection. However, the crystallographic texture in a wide hatch space condition manifested a random distribution and constituted a fine mixture of the β and α2 phases. For the first time, these results will offer an understanding of an anisotropic microstructure control via the L-PBF process and ensure the tailoring of the mechanical properties in the β-solidifying γ-TiAl-based alloys by approaching hatch spacing control.Graphic

Crystallographic texture formation in Fe-9wt%Si alloy during deformation and phase transition at high pressure

SUMMARY The seismic anisotropy of the Earth's solid inner core has been the topic of much research. It could be explained by the crystallographic preferred orientation (CPO) developing during convection. The likely phase is hexagonal close-packed iron (hcp), alloyed with nickel and some lighter elements. Here we use high energy synchrotron X-rays to study CPO in Fe-9wt%Si, uniaxially compressed in a diamond anvil cell in radial geometry. The experiments reveal that strong preferred orientation forms in the low-pressure body-centred cubic (bcc) phase that appears to be softer than pure iron. CPO is attributed to dominant {110}&amp;lt;111&amp;gt; slip. The onset of the bcc→hcp transition occurs at a pressure of ≈15 GPa, and the alloy remains in a two phase bcc + hcp state up to 40 GPa. The hcp phase forms first with a distinct {11$\bar{2}$0} maximum perpendicular to compression. Modelling shows that this is a transformation texture, which can be described by Burgers orientation relationship with variant selection. Experimental results suggest that bcc grains oriented with &amp;lt;100&amp;gt; parallel to compression transform into hcp first. The CPO of the hcp changes only slowly during further pressure and deviatoric stress increase at ambient temperature. After heating to 1600 K, a change in the hcp CPO is observed with alignment of (0001) planes perpendicular to compression that can be interpreted as dominant (0001)&amp;lt;11$\bar{2}$0&amp;gt; slip, combined with {10$\bar{1}$2}&amp;lt;$\bar{1}$011&amp;gt; mechanical twinning, which is similar to the deformation modes suggested previously for pure hcp iron at inner core conditions.

Regularities of structure and texture development in austenitic steel during cold rolling and heat treatment

The paper studies the regularities of the structure and texture formation in austenitic steel AISI 304 under cold rolling and subsequent heat treatment. Regularities of structure and texture formation depending on the rolling type and deformation degree were established. The ratios of main texture components, the volume fractions and the distortion of the martensite's crystalline lattice were analyzed. It is shown that mechanisms of the austenite martensite phase transformation in the course of cold rolling may change depending on various deformation schemes, as well as mechanisms of the reverse phase transformation variate under subsequent annealing. Herewith depending on the rolling type and deformation degree, the crystallographic texture formation of the nucleating austenite under the heat treatment can have single component or multi-component character and follows different orientation relations. The more scattered martensite texture after deformation results in the formation of fine-dispersed austenite, which hardens the material keeping a sufficient level of plasticity. The work was carried out with the financial support of&nbsp;the Ministry of Science and Higher Education of Russian&nbsp;Federation (Agreement No. 075-15-2021-1352).

Effects of interfacial interactions between metal and process control agents during ball milling on the microstructure of the milled Fe-based nanocrystalline alloy powder

Fe–Si–B–P–Cu nanocrystalline alloy were treated with ball-mill using a lubricant as a process control agent (PCA). The resulting alloy powder is a strong candidate material for soft magnetic composites. Two ball milling methods (continuous and interval) were employed to control the interactions between the PCA and the alloy surface, and their effect on the microstructure of the prepared alloy particles was investigated. The alloy sheet was broken into small pieces and deformed plastically into flake-shaped particles regardless of the ball milling method implemented. Friction-force microscopy of the alloy immersed in the PCA revealed that the friction coefficient of the alloy surface exposed to air for a certain period was higher than that of the unexposed alloy surface (immediately after polishing). During ball milling, the ratio of the newly generated surface to the oxidized surfaces of the alloy subjected to interval milling was smaller than that of the alloy subjected to continuous milling. Therefore, the friction coefficient of the surface of the alloy subjected to interval milling was higher than that of the alloy subjected to continuous milling. Synchrotron radiation analysis revealed that the alloy subjected to interval milling exhibited enhanced surface friction, showing an obvious steepness and inflection in the diffraction intensity as a function of the tilt angle based on the Schulz reflection method. This indicates formation of crystallographic texture in α-Fe grains in an amorphous matrix. Hence, we demonstrated successfully that the ball milling process induced a crystallographic texture in the Fe-based nanocrystalline alloy due to plastic deformation due to the enhanced surface friction. The surface of the alloy was prepared based on the effect of the interfacial interactions between the alloy surface and the PCA.

Directionally solidified high-entropy (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)3Al5O12/Al2O3 eutectic with outstanding crystallographic texture formation capability

Crystallographic texture control is the critical challenge for directionally solidified eutectic (DSE) ceramics. We herein report a high-entropy (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)3Al5O12/Al2O3 DSE ceramic that shows outstanding crystallographic texture formation capability. Based on comprehensive observations of phase composition and eutectic microstructure characteristics, the single crystal phases of high-entropy (5RE0.2)3Al5O12 (RE = rare earth) and Al2O3 are obtained within a much-shortened growth distance (within 15 mm) than those of the single rare earth containing RE3Al5O12/Al2O3 counterparts (typically ≥ 80 mm). The rapid formation of stable crystallographic texture is significant for microstructure control in DSE processing and uniformity of mechanical property along the whole material.

Structure and texture in rolled Fe82Ga18 and (Fe82Ga18)99B1 alloys after annealing under high magnetic field

The structure and crystallographic texture formation processes in two Fe–Ga magnetostrictive alloys during annealing of deformed samples under high magnetic field (HMF) 20 T have been studied. It was shown that the effect of the magnetic field on the structure transformation during annealing depends on the features of the recrystallization in alloys. In the case of recrystallization in a single-phase binary Fe-Ga alloy, the application of HMF along the rolling direction promotes the formation of <100> grains along this direction. This leads to a twofold increase in the magnetostriction of the polycrystalline sample. In the same alloy, but with the presence of particles of the second phase, HMF does not affect the texture. The reasons for this phenomenon were discussed. In addition, it was found that in both alloys, the application of HMF during annealing retards the processes of structure evolution.

Tribologically induced crystal rotation kinematics revealed by electron backscatter diffraction

Tribological loading of metals induces microstructural changes by dislocation-mediated plastic deformation. During continued sliding, combined shear and lattice rotation result in the formation of crystallographic textures which influence friction and wear at the sliding interface. In order to elucidate the fundamental lattice rotation kinematics involved in this process during the early stages of sliding, we conducted unlubricated, linear single pass sliding experiments on a copper bicrystal using sapphire spheres. Electron backscatter diffraction (EBSD) performed directly on the bulk surface of the wear tracks in the vicinity of the grain boundary reveals crystal lattice rotations by approximately up to 35°. Predominantly, the tribologically induced crystal rotations appear to be kinematically constrained to rotations around the transverse direction (TD) and occur in both grains, irrespective of load (2 to 8 N). We demonstrate that inverting the sliding direction (SD) inverts the sense of crystal rotation, but does not change the principal nature of rotation for the majority of indexed EBSD data. A lower proportion of the crystal lattice rotates much farther around TD (roughly up to 90°), accompanied by a superimposed crystal rotation around ±SD. Analysis reveals that sliding direction and grain orientation exert a systematic influence of how crystal rotations are accommodated. This is rationalized in terms of geometry, anisotropic wear track profiles and slip traces. Under specific conditions, combined crystal rotation and twinning are observed. These detailed insights into the fundamental nature of tribologically induced lattice rotation kinematics provide important guidance for applied research targeting materials with superior tribological properties.

Influence of powder characteristics on densification via crystallographic texture formation: Pure tungsten prepared by laser powder bed fusion

The laser powder bed fusion (LPBF) of pure tungsten for the fabrication of near-fully dense components is challenging owing to the intrinsic properties of tungsten. In this study, routine, gas-atomized, and plasma-processed tungsten powder samples were characterized for their powder shape, size distribution, tapped density, and flowability, and then used to fabricate parts using identical LPBF process parameters to evaluate the influence of the powder characteristics on the metal densification and microstructure. The plasma-processed W powder showed a relative density of 98.7%, the highest value yet to be reported, at a baseplate temperature of 80 °C owing to the higher tapped density and improved flowability of the powder, which result in high-quality powder bed formation. In addition, numerical simulations were conducted to estimate the effect of the powder quality on laser energy absorption and, thus, melt pool formation. The results reveal that enhanced powder characteristics result in an increased density and prevent lack of fusion while tuning the grain boundary characteristics and strengthening the crystallographic texture, which resulted in decreased cracking owing to less crack-sensitive grain boundaries and increased hardness of the as-built W components.

Role of laser powder bed fusion process parameters in crystallographic texture of additive manufactured Nb–48Ti alloy

Additive manufacturing, known as “3D printing”, is a set of manufacturing technologies that can build parts with complex geometries in a process by adding layers of powder material. The laser powder bed fusion (L-PBF) process is characterized by selectively melting layers of particulate material at a micrometer scale in repetitive patterns. This technology is expected to improve Young's modulus of metallic biomaterials, by controlling the microstructure and crystallographic texture– influenced by the laser power and scanning speed parameters which promote an oriented heat extraction. Implant materials should have low Young's modulus, to avoid a large mismatch with that of the bones. This work investigates the role of the laser power and scanning speed on microstructure and crystallographic texture formation of the Nb–48Ti alloy, fabricated by laser powder bed fusion process, using pre-alloyed plasma atomized powder. The microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM), backscattered electron diffraction technique (EBSD) for crystallographic texture, and Young's modulus was obtained indirectly via EBSD data. The microstructure showed a cellular dendritic solidification morphology formed by epitaxy at the edge of the melt pools. Texture results indicated that higher values of power and scanning speed favored the increasing of a near-cube-on-face texture and a reduction in Young's modulus.

Specific features of crystallographic texture formation in BCC-FCC transformation in extruded brass

Crystallographic features of body-centered cubic to face-centered cubic transformation were studied in an extruded brass product. X-ray phase analysis, scanning electron microscopy with electron microprobe analysis, and orientation microscopy based on diffraction of back-scattered electrons were used. A sample after treatment consisted of the β′-phase (Cu0.55Zn0.45, structural type B2) and α-phase (Cu0.65Zn0.35, structural type A1) at 30:70. Integral textures (within the product) of phases were axial with axes parallel to the elongation direction in extrusion:< 110 >for β’ and< 100 >for α. Local textures of phases are described as limited and consisting of a set of components. For β′ – {001}< 110 >, with scattering up to± 25° around the axis< 110 >; and {110}< 110 >consisting of three components – one {110}< 110 >and two {110} ± 24° around the axis< 110 >; for α – {001}< 100 >(strong) and two of {110}< 111 >(weak). It was shown that components of local textures of the β′- and α-phases were associated by orientation relationships close to Kurdjumov-Sachs orientation relationships. A small number of limited textural components formed as a result of β(BCC)→α(FCC) transformation realized as per multi-variant orientation relationships is explained by the formation of nuclei of a new phase at special boundaries close to coincidence site lattice boundaries Σ3 and Σ33.

Unique crystallographic texture formation in Inconel 718 by laser powder bed fusion and its effect on mechanical anisotropy

Additive manufacturing offers an exclusive way of anisotropic microstructure control with a high degree of freedom regarding variation in process parameters. This study demonstrates a unique texture formation in Inconel 718 (IN718) using a bidirectional laser scan in a laser powder bed fusion (LPBF) process for tailoring the mechanical properties. We developed three distinctive textures in IN718 using LPBF: a single-crystal-like microstructure (SCM) with a <110> orientation in the build direction (BD), crystallographic lamellar microstructure (CLM) with a <110>-oriented main layer and <100>-oriented sub-layer in the BD, and polycrystalline with a weak orientation. The microstructure observations and finite element simulations showed that the texture evolution of the SCM and CLM was dominated by the melt-pool shape and related heat-flow direction. The specimen with CLM exhibited a simultaneous improvement in strength and ductility owing to the stress-transfer coefficient between the <110>-oriented main and <100>-oriented sub-grains, showing superior mechanical properties compared to cast-IN718. This behavior is largely attributed to the presence of the boundary between the main and sub-layers (crystallographic grain boundary) lying parallel to the BD uniquely formed under the LPBF process. Furthermore, the strength–ductility balance of the part with the CLM can be controlled by changing the stress-transfer coefficient and the Schmidt factor through an alteration of the loading axis. Control of the crystallographic texture, including the CLM formation, is beneficial for tailoring and improving the mechanical performance of the structural materials, which can be a promising methodology.

Regularities of Crystallographic Texture Formation in Products Obtained by Selective Laser Powder Melting

As examples of austenitic steel 316L, nickel alloy (Inconel 625) and titanium alloy VT1-0, the regularities of the development of crystallographic texture in monolithic samples and lattice structures obtained by selective laser melting (SLM) of powder are considered. Crystallization of all of these alloys is carried out by the formation of crystals with a cubic structure {100} <001> (bcc or fcc). Upon subsequent cooling, the titanium samples additionally undergo a β→α phase transformation while maintaining the Burgers orientation relation. A sharp cubic texture {100}<001> is formed in the middle-height layers of a monolithic product, which determines the anisotropy of the properties of SLM samples. The layer-by-layer change in the crystallographic texture is associated with the growth of columnar crystals of the cubic phase, which are formed due to the thermal effect of the molten region on the underlying layers, which determine the orientation of the crystal during its crystallization. This texture is typical for both the fcc-phase of steel and the bcc-titanium phase. In the case of the formation of lattice structures, columnar crystals with a preferred orientation of <001> along the growth direction are formed in the central part of the ribs and nodes along the diameter of the structural elements. On the basis of the crystallographic texture of the steel lattice structures and the mechanical properties of the monolithic specimens, the strain curves of the lattices under their compression were calculated.

Prediction of Crystallographic Texture Formation in Polycrystalline Samples under Severe Plastic Deformation Based on a Two-Level Statistical Elasto-Viscoplastic Model

Prediction of Crystallographic Texture Formation in Polycrystalline Samples under Severe Plastic Deformation Based on a Two-Level Statistical Elasto-Viscoplastic Model

Formation of crystallographic texture in Fe-Ga alloys during various types of plastic deformation and primary recrystallization

The regularities of texture formation in FeGa-based alloys during deformation at medium degrees (about 60 %) and primary recrystallization were studied. Deformation was realized by two methods: rolling and hydrostatic extrusion to study the deformation behavior and the texture formation processes. After deformation, the samples were subjected to annealing to initiate primary recrystallization. The structure and texture after deformation and recrystallization were studied using EBSD technique. It was shown that FeGa-based alloys have a greater tendency to form {hkl}<100> texture during primary recrystallization, compared to other wide-used soft magnetic materials with body-centered cubic (bcc) lattice. Alloying by boron enhances this tendency and results in a uniform texture after recrystallization. As a result, a high level of functional properties was achieved through the implementation of cost-effective deformation and annealing operations.

Effect of Scan Length on Densification and Crystallographic Texture Formation of Pure Chromium Fabricated by Laser Powder Bed Fusion

Processing of pure chromium (Cr) encounters substantial challenges due to its high melting point and intrinsic brittleness. Although laser powder bed fusion processing (LPBF) offers a novel processing approach by reaching the temperature required to melt pure Cr, the high ductile-to-brittle transformation temperature (DBTT) of pure Cr prevents the density of the as-built Cr component from reaching the level of industrial acceptance. This study focuses on raising the quality of the as-built pure Cr components to the industrial level while considering the effect of scan length on densification and crystallographic texture. It was found that short scan length induced by feature size improved the density of as-built specimens while strengthening the texture suggesting uniform heat distribution and lower thermal gradients as a result of short time intervals in scanning tracks and layers. It was discovered that cracking caused by residual stress was detrimental to densification due to the DBTT characteristic of pure Cr, which was localized at high-angle grain boundaries (HAGBs) with high misorientation. The decrease in density and misorientation of HAGBs owing to the increase in grain size and texture strength, respectively, improved the density of as-built Cr up to 97.6% and altered its mechanical properties. Therefore, these findings offer new insight into the LPBF processing of metals with high DBTT characteristics.

Copper electrodeposition under a weak magnetic field: effect on the texturing and properties of the deposits

The effect of a weak magnetic field (induction of 0.5 to 0.7 mT) on the electrodeposition process and the formation of crystallographic texture, morphology and properties of copper deposits has been considered. Electrodeposition studies were performed using cyclic voltammetry, chronoamperometry, and chronopotentiometry. X-ray texture analysis and scanning electron microscopy observations were used to study the texture and the morphology of the copper deposits. Some of their properties were obtained by measuring their microhardness and reflectivity. The effects of decreasing the rate of copper electrodeposition, enhancing texture formation and refinement of grain aggregates of the surface of copper films under the influence of a weak magnetic field have been evidenced. The interrelation of the texture and morphology of the copper electrodeposit surface with their microhardness and reflectivity have been revealed. The conditions for obtaining copper deposits with enhanced microhardness and reflectivity have been determined. It is shown that the electrochemical deposition with a weak magnetic field is a promising direction for obtaining materials with desired properties, without using strong magnetic fields and adding surfactants to the electrolyte.