Development Of Crystallographic Orientation Research Articles

Aging Treatment Induces the Preferential Crystallographic Orientation of αs in the Near-α Titanium Alloy Ti60

In this article, we subjected the Ti60 alloy to solid-solution treatment at 1020 °C and aging treatment at 600 °C, respectively, achieving a bimodal microstructure. The microstructures obtained after aging treatment showed no significant difference in the primary α-phase content, size, and width of the lamellar α phase. This suggests that the final microstructure morphology is primarily determined by the solid-solution temperature, with the aging process exerting less pronounced effects on microstructural alterations. Furthermore, we investigated the effect of solid-solution and aging treatment on the crystallographic orientation evolution of the secondary α phase (αs) in the near-α titanium alloy Ti60. The αs phase displays a random orientation in solid-solution treatment sample, while it demonstrated a preferential {0 1 −1 0} orientation after aging treatment. This interesting phenomenon is attributed to the enhanced variant selection resulting from the dissolution of variant near 60° and 90° during aging. Furthermore, the αs with {0 1 −1 0} orientation nucleated at the grain boundary and coalesced into larger αs lath with increasing aging time, further contributing to the αs {0 1 −1 0} texture.

Ion- and temperature-induced 3-dimensional nanoscale patterning in Ti1-xAlxN deposited by High Power Impulse Magnetron Sputtering

We report on surface-driven self-organization in the TiN-AlN binary system during ion-assisted deposition at elevated temperatures. With an Al:Ti ratio slightly above the boundary of stable cubic growth, various morphologies from single-phase films to highly ordered two-phase films with v-shaped and oblique, striped structures were obtained. The high metal ion fractions and high ion energies obtained by High Power Impulse Magnetron Sputtering result in unique morphologies that are not accessible by conventional magnetron sputtering. A comprehensive structural and chemical analysis of the two-phase films is presented to enlighten the mechanism of phase separation and crystallographic orientation evolution.

The effect of deformation temperature on the microstructure and crystallographic orientation evolution of Ti60 alloy after annealing

The effect of deformation temperatures, 900 °C and 980 °C, on the microstructure and crystallographic orientation evolution of Ti60 alloy with lamellar microstructure had been studied in our previous work. In this paper the characterizations of the microstructure and texture as well as the macrozone evolution after annealing at 1020 °C were studied for samples deformed at the both temperatures with 70% height reduction by optical microscope (OM), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). A fine homogenous bimodal microstructure in terms of morphology and orientation distribution was found in the sample deformed at 900 °C after annealing. In contrast, a sharp textured microstructure with macrozones was also produced after annealing in the sample that had deformation at 980 °C. Moreover, the prior β texture and the primary α texture were analyzed. The formation of the main transformed α texture, <11–20> parallel to compression direction (CD) fiber texture, which was reinforced with an increase in deformation temperature, was found to be related to the <100>//CD β fiber texture and variant selection effected by primary α grains. Finally, the mechanisms by which the macrozones formed for bimodal microstructure are discussed. In this study, a relationship between the microstructure and texture evolution is established to reveal the influence of deformation temperature on the microstructue and crystallographic orientation of Ti60 alloy after annealing.

Evolution of crystallographic orientation and microstructure in the triangular adapter of grain continuator of a 3rd-generation single crystal superalloy casting during directional solidification

The evolution of the crystallographic orientation and the microstructures in triangular adapters of grain continuators (GCs) with different flare angles and thicknesses prepared by a 3rd-generation single crystal (SX) superalloy were investigated under different withdrawal rates. The microstructures were observed by an optical microscope and the crystallographic orientation of the GCs was measured by electron backscatter diffraction (EBSD). The directional solidification process was simulated by a commercial simulation software ProCAST. The experimental results showed that the [001] misorientation between both sides of the GCs at top cross section increased with the increasing of the flare angle, the thickness of specimens, and the withdrawal rate. These phenomena were attributed to the changing of the isotherm morphology in the mushy zones and the velocity of the solidification front. As for a low flare angle, the freckle defect formed at one side of specimens under the withdrawal rate of 1 mm/min. With the increasing of flare angle, the freckle defect cannot be found at the same position of the specimens. The formation mechanisms of freckle defect in the triangular adapters of GCs were further discussed.

Research on Modeling Crystallographic Texture Evolution of Al Alloy 7075

Crystallographic texture is related to the anisotropy or isotropy of material physical properties, including mechanical performance. The crystallographic effect in micromachining is more significant than that in macro-processing owing to that the depth of the cut and the grain size are in the same order. It is of great significance to model the crystallographic texture evolution induced by mechanical and thermal load during micro-machining to investigate the surface integrity and performance of the finished product. This study performed hot deformation experiments of Al alloy 7075 (AA7075) under various input parameters, including the temperature, temperature rate, stain rate, and strain, which was designed using the Taguchi method. Following that, crystallographic orientation of the samples before and after the deformation was tested using electron back-scattered diffraction (EBSD). Then, the crystallographic texture evolution was modeled with the parameters obtained by fitting a part of the experimental data. The crystallographic texture evolution of AA7075 under different levels of input parameters is studied and analyzed. Finally, the sensitivity of crystallographic orientation evolution to the process parameter is analyzed. The results indicate that these four input parameters have a significant impact on some crystallographic texture of the specimens. The proposed model is instructive in the future investigation of micromachining and microstructure evolution.

Evolution of crystallographic orientation, columnar to equiaxed transformation and mechanical properties realized by adding TiCps in wire and arc additive manufacturing 2219 aluminum alloy

2219Al/TiCps composites were deposited by the wire and arc additive manufacturing method. The effects of TiCps content on the phase transformation, average grain size, crystal orientation, and mechanical properties of the deposited 2219 aluminium alloys were investigated as the variation of TiCps fraction is from 0.5 wt% to 2.0 wt%. The results show that the addition of 5 µm TiCps can effectively reduce the nucleation free energy of the system, which provided an opportunity for nuclei to grow on the surface of TiCps. The average grain size first decreased, then increased with the increase of TiCps weight fraction. Also, the EBSD testing results show the texture intensity both the Al-matrix and the θ-CuAl2 phase gradually decreased with increasing TiCps fraction. TiCps played an important role in generating nucleation undercooling (ΔTnu, 0.38 °C), which could be used to counteract the constitutional supercooling (ΔTcs) caused by solute segregation, and further promoted the transformation of granular θ-CuAl2 phase to a fine spot-like one within the grains. The fine spot-like phase possessed a strong interfacial bonding with the Al-matrix, thereby the mechanical properties of the deposited 2219 aluminium alloy were strengthened. Eventually, the deposited alloy exhibited a tensile strength around 405 MPa, and the elongation was up to 15.6%.

Comparative study on crystallographic orientation, precipitation, phase transformation and mechanical response of Ni-rich NiTi alloy fabricated by WAAM at elevated substrate heating temperatures

In this investigation, a Ni-rich NiTi alloy was in-situ deposited with different substrate heating temperatures and the evolution of crystallographic orientation, precipitation, phase transformation, and mechanical responses were evaluated. The experimental results indicated that with the increment of substrate heating temperature from 150 °C to 350 °C, the average B2 grain size and the high angle grain boundaries (HAGBs) gradually increased from 53.44 μm to 85.38 μm and 53.6%–62.4%, respectively. The crystallographic texture exhibited a dominant, strong (001) orientation with comparatively weak (111) and (101) orientations in all conditions and the intensity of {100}<001> increased slightly as the substrate heating temperature increased. Moreover, Ni4Ti3 precipitates with an inhomogeneous size distribution were identified within the B2 NiTi matrix. Increasing the substrate heating temperature coarsened the Ni4Ti3 precipitates. All the phase transformation temperatures increased when the substrate heating temperature increased, indicating that the martensitic transformation is more likely to occur. As the substrate heating temperature increased from 150 °C to 350 °C, the yield stress and ultimate tensile stress decreased from 683.9 to 513.1 MPa and 855.2 to 743.8 MPa, respectively, and the ductility decreased from 6.90% to 6.13%. In addition, a remarkable εir, poor recovery ratio and a broad stress hysteresis were obtained during the initial deformation of the cyclic loading-unloading tension. The highest recoverable strain (εre), recovery ratio and elastic energy storage efficiency (ƞ) were obtained in samples processed with the lowest substrate heating temperature. These findings provide useful references concerning process optimization in fabricating Ni-rich NiTi components by WAAM with acceptable microstructure and mechanical properties.

Texture evolution in selective laser melted maraging stainless steel CX with martensitic transformation

Due to high local cooling rates and non-equilibrium directional solidification conditions, selective laser melting (SLM) processed metals exhibit microstructural and textural features significantly different from the conventionally processed ones. The evolution of crystallographic orientations in a maraging stainless steel (commercially known as stainless steel CX) sample fabricated by the SLM process was studied through experimental and modelling approaches Electron backscattering diffraction analysis showed that the dominant texture components in martensite and austenite phases are <111>|| building direction and <011>|| building direction, respectively. Texture simulation indicated that the formation of crystallographic orientations in the studied sample is the result of two consecutive phase transformations, from initially solidified delta ferrite phase with dominant cube fiber texture to austenite and austenite to martensite.

Evolution of crystallographic orientation, precipitation, phase transformation and mechanical properties realized by enhancing deposition current for dual-wire arc additive manufactured Ni-rich NiTi alloy

Ni-rich NiTi alloys were deposited using the in-situ alloying wire arc additive manufacturing (WAAM) method, with varying deposition currents from 80 A to 120 A. The effects of deposition current on the crystal orientation, precipitation, phase transformation and mechanical properties of the WAAM-deposited NiTi alloys were investigated. The results show that increasing the deposition current during the WAAM process would result in noticeable coarsening of B2 grain and an increased volume fraction of high angle grain boundaries (HAGBs). Also, the texture intensity gradually decreased with increasing deposition current. The fabricated components are dominated by the B2 phase with quantities of Ni4Ti3 precipitates in all samples. When increasing the deposition current during the WAAM process, the size of Ni4Ti3 precipitates generally increased and gradually decomposed into a stable Ni3Ti phase which could be detected in the sample produced at 120 A. Furthermore, all of the characteristic phase transformation temperatures increased with the deposition current while the ultimate tensile strength dropped from 927.9 MPa to 613.8 MPa and elongation reduced from 8.7 % to 5.6 %. The cyclic loading-unloading tests revealed that similar trends for the evolution of irreversible strain (εir), recoverable strain (εre), recovery ratio, and elastic energy storage efficiency (η) during cycling were obtained in all samples processed with different deposition currents. The highest εre of 3.2 % and the highest recovery ratio of 53.9 % were obtained in the sample processed with 80 A at an applied stress of 700 MPa for ten cycles. The change of mechanical properties with varying deposition current is due to a combination of factors including precipitation hardening effect, grain refinement effect, and crystal orientation. These results can be useful for optimizing WAAM process parameters to fabricate NiTi components with acceptable structural properties.

Quasi-In-Situ EBSD Observation of the Orientation Evolution in Polycrystalline Tantalum During Rolling Deformation

The evolution of crystallographic orientation of polycrystalline tantalum (Ta) during rolling was characterized by electron backscatter diffraction technique in a quasi-in-situ way, and the microstructure and microtexture before and after the deformation were characterized and analyzed, respectively. In the specimen, 164 individual grains were exacted singly from the testing region and their corresponding orientations were reconstructed and analyzed, respectively. Results show that the heterogeneous deformation in a grain can be reflected by the accidented surface microstructure. Moreover, the orientations close to {111} orientations came closer to the {111} corner, while the orientation evolution is more complicated for the orientations close {100} corner, indicating that the evolution of these orientations close to {100} corner seemed to be irregular.

Deformation of metals under dynamic loading: Characterization via atomic-scale orientation mapping

Crystallographic orientation evolution of metals under dynamic loading conditions is of considerable interest, but rarely explored in simulations at atomistic scales. Here we present a methodology for atomic-scale orientation mapping, with atomic positions as input. The rotation matrix representing the orientation of a crystallite consisting of a central atom and its nearest neighbors, and corresponding Euler angles, are calculated, which are used for orientation analysis and visualization. As application cases, we investigate orientation evolution related to grain boundary migration, deformation twinning, deformation within grain interior, partial grain rotation, and grain refinement in representative FCC, BCC and HCP metals under dynamic loading conditions including shock loading.

Evolution of crystallographic orientation during thermomechanical fatigue of heat-resistant stainless steel

We present the evolution of crystallographic orientation and microstructure during thermomechanical fatigue (TMF) of heat-resistant cast austenitic stainless steel at peak temperatures reaching 950 °C using the electron backscatter diffraction (EBSD) method. Higher restraints or peak temperatures induced larger crystal misorientation by geometrically necessary dislocations (GNDs), forming dislocation walls or subgrains in the grains. Networked carbide clusters in the microstructure locally amplified the misorientation in the adjacent matrix and initiated fatigue cracks. The mean value of cumulative misorientations over a specific distance in the matrix was linearly proportional to the cyclic plastic strain.

Crystallographic orientation evolution during the development of tri-modal microstructure in the hot working of TA15 titanium alloy

The crystallographic orientation evolution and its dependence on processing parameters during the development of tri-modal microstructure of titanium alloy were studied by the thermal-mechanical processing tests and electron backscatter diffraction (EBSD) examination. It is found that the development of tri-modal microstructure undergoes two stages: firstly, bimodal microstructure consisting of equiaxed α (αp) and transformed β matrix (βt: a mix of secondary α phase (αs) and β phase) is formed after first-stage near-β forging; then, the tri-modal microstructure consisting of αp, lamellar α phase (αl) and βt are obtained after the following heat treatment. The equiaxed α in final tri-modal microstructure does not follow the Burgers orientation relationship (OR) with β phase. Its crystallographic orientation is hardly influenced by the hot processing parameters. The lamellar α in tri-modal microstructure is right the undissolved secondary α of bimodal microstructure (obtained after first step) during the heating process of the second step. Both of them keep the Burgers OR with β phase, however, the dissolution of secondary α present selectivity to some extent making the variant selection degree of lamellar α greater than that of secondary α. The variant selection degree of lamellar α in tri-modal microstructure decreases with increasing the cooling rate, deformation degree and strain rate of near-β forging. The secondary α in tri-modal microstructure is precipitated from β phase and obeys the Burgers OR with β phase during the cooling process of the second step. The existing lamellar α plays a strengthening role in the variant selection during its precipitation. While the cooling rate, deformation degree and strain rate of near-β forging show limited effect on the probabilities of each type of misorientation and variant selection degree of secondary α.

Study of Anisotropic Plastic Behavior in High Pressure Torsion of Aluminum Single Crystal by Crystal Plasticity Finite Element Method

In this study, a crystal plasticity finite element method (CPFEM) model has been developed to investigate the anisotropic plastic behavior of (001) aluminum single crystal during high-pressure torsion (HPT). The distributions of equivalent plastic strain and Mises stress recorded on the sample surface are presented. The directional variations of plastic strain and Mises stress with the development of four-fold symmetry pattern are observed along the sample circumference. The crystallographic orientation evolution along the tangential direction is studied, and the corresponding lattice rotation and slip trace are predicted, respectively. The plastic anisotropy mechanism is discussed in detail based on the theory of crystal plasticity. The simulation results reveal that the differences in slip systems activation (dominant slip and multiple slips) are responsible for the anisotropic plastic deformation in HPT.

Direct measurement of critical resolved shear stress of prismatic and basal slip in polycrystalline Ti using high energy X-ray diffraction microscopy

Knowledge of the critical resolved shear stress (CRSS) values of different slip modes is important for accurately modeling plastic deformation of hexagonal materials. Here, we demonstrate that CRSS can be directly measured with an in-situ high energy X-ray diffraction microscopy (HEDM) experiment. A commercially pure Ti tensile specimen was deformed up to 2.6% strain. In-situ far-field HEDM experiments were carried out to track the evolution of crystallographic orientations, centers of masses, and stress states of 1153 grains in a material volume of 1.1 mm × 1 mm × 1 mm. Predominant prismatic slip was identified in 18 grains, where the orientation change occurred primarily by rotation around the c-axis during specimen deformation. By analyzing the resolved shear stress on individual slip systems, the estimated CRSS for prismatic slip is 96 ± 18 MPa. Predominant basal slip was identified in 22 other grains, where the orientation change occurred primarily by tilting the c-axis about an axis in the basal plane. The estimated CRSS for basal slip is 127 ± 33 MPa. The ratio of CRSSbasal/CRSSprismatic is in the range of 1.7–2.1. From indirect assessment, the CRSS for pyramidal 〈c+a〉 slip is likely greater than 240 MPa. Grain size and free surface effects on the CRSS value in different grains are also examined.

Effect of heat treatment on the crystallographic orientation evolution in a near-α titanium alloy Ti60

The crystallographic orientation of equiaxed primary α (αp) phase is one of the main factors that determine the final texture/microtexture and mechanical properties for near-α titanium alloys. By annealing a forged Ti60 alloy pancake at 1030 and 1040 °C in the α+β two-phase field, two homogeneous bimodal microstructures were obtained, the intensity of secondary α in the {0001} pole figure increasing with the annealing temperature. In this study, the influence of annealing temperature on the crystallographic orientation evolution in the pancake was studied using an electron backscattered diffraction analysis method. In particular, a misorientation angle θ associated with (βΔJβBOR) that could quantitatively evaluate the deviation of the orientation relationship (OR) between αp and the surrounding β grains from Burgers OR was used to understand the role of the αp phase, which is considered as an anisotropic precipitate, in the texture evolution during annealing in the two-phase field. It was found that the αp grains with small θ are more readily preserved during the annealing, while their pinning effect is relatively small, resulting in faster growth of the neighboring β grains. A possible effect of heterogeneous local orientation distribution on the microstructure during the annealing process is also discussed.

Effect of Base Material on Microstructure and Texture Evolution of a Ti–6Al–4V Electron-Beam Welded Joint

The effect of base material (BM) on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior β grains was studied by advanced electron backscattered diffraction data processing. The inhomogeneity of microstructure within welded joint was formed due to the different microstructures of BM. By comparing microstructure details of the welded joint, including microstructure morphology and crystallographic orientation with those of the base material, it can be found that both the microstructure morphology and crystallographic orientation of the EBW joint would be controlled by BM.

Development of a multi-scale simulation model of tube hydroforming for superconducting RF cavities

This work focuses on finite element modeling of the hydroforming process for niobium tubes intended for use in superconducting radio frequency (SRF) cavities. The hydroforming of tubular samples into SRF-relevant shapes involves the complex geometries and loading conditions which develop during the deformation, as well as anisotropic materials properties. Numerical description of the process entails relatively complex numerical simulations. A crystal plasticity (CP) model was constructed that included the evolution of crystallographic orientation during deformation as well as the anisotropy of tubes in all directions and loading conditions. In this work we demonstrate a multi-scale simulation approach which uses both microscopic CP and macroscopic continuum models. In this approach a CP model (developed and implemented into ABAQUS using UMAT) was used for determining the flow stress curve only under bi-axial loading in order to reduce the computing time. The texture of the materials obtained using orientation imaging microscopy (OIM) and tensile test data were inputs for this model. Continuum FE analysis of tube hydroforming using the obtained constitutive equation from the CP modeling was then performed and compared to the results of hydraulic bulge testing. The results show that high quality predictions of the deformation under hydroforming of Nb tubes can be obtained using CP-FEM based on their known texture and the results of tensile tests. The importance of the CP-FEM based approach is that it reduces the need for hydraulic bulge testing, using a relatively simple computational approach.

Investigations on the Crystallographic Orientation Induced Surface Morphology Evolution of ZnO Thin Films and Their Wettability and Conductivity

The intrinsic zinc oxide (ZnO) thin films with controllable crystallographic orientation have been synthesized on Si(100) substrates using plasma-enhanced chemical vapor deposition (PECVD) system without any buffer layer. Based on X-ray diffraction (XRD) results, the evolution of crystallographic orientation of ZnO thin films from polar c-plane (0002), polar c-plane and nonpolar m-plane (1010) coexist to nonpolar m-plane and a-plane (1120) coexist was achieved by a simple factor of controlling synthesized temperature. The plane-view morphological images exhibited that the surface texture and grain shape of ZnO thin films could have evolved from hexagonal to stripelike grains when the ZnO crystallographic orientation changed from perpendicular to parallel to the substrate. The characterization analysis indicated that the zinc precursor [diethylzinc (DEZn), Zn(C2H5)2] played a key role on the crystallographic orientation evolution of ZnO thin films during the early stage of the growth process because DEZn...

Facilitating Basal Slip to Increase Deformation Ability in Mg-Mn-Ce Alloy by Textural Reconstruction Using Friction Stir Processing

The widespread application of wrought magnesium alloys is hampered by their insufficient formability at room temperature. The tensile ductility of a newly developed Mg-Mn-Ce alloy has been dramatically improved by friction stir processing (FSP). The microstructure of the stir zone was characterized mainly by elongated fine grains which were highly separated by low-angle grain boundaries because of the high contribution of continuous dynamic recrystallization. A new {0002} distribution with high basal plane tilt angles which facilitated 〈a〉 basal slip when the specimens were pulled along the FSP direction was obtained. Both the enhanced basal slip and crystallographic orientation evolution of Mg crystals increased the strain hardening exponent of the FSP specimen, and hence improved its tensile ductility. A material flow model, developed based on the local textural evolution, could reasonably explain the phenomenon that the FSP specimen exhibited warping and a high normal anisotropy ratio during tensile test.