Grains Of Different Orientations Research Articles

Rapid acquisition of digital fingerprints of Ti-6Al-4V macrotexture from machining force measurement data

Titanium alloys display anisotropic deformation properties due to the hexagonal close-packed (hcp) crystal structure of the α-phase. When subjected to localised deformation during machining, this behaviour influences fluctuations in the cutting force response of the material as the tool encounters grains of different orientations. In this research, cutting force signals acquired during face turning of Ti–6Al–4V possessing a lamellar α colony structure have been spatially mapped demonstrating the ability to identify microstructural features such as prior-β grain boundaries, grain boundary α, and α colonies. Measured cutting forces have been correlated to texture using orientation information acquired from large area EBSD analysis. A relationship between the misalignment of the crystallographic a slip vector with respect to the cutting direction and the passive cutting force response has been established, demonstrating a rise in cutting forces as this misalignment is increased. This novel approach to in-process materials evaluation offers manufacturers the potential of a powerful digital quality assurance tool, with the results presented here demonstrating the possibility for rapid characterisation of entire component surfaces, revealing microstructural features, and inferring the crystallographic orientation of macrotextured regions in Ti–6Al–4V.

Deformation behaviour of the silicon doped metastable Fe50-xMn30Co10Cr10Six complex concentrated alloy using experiments and crystal plasticity simulations

Deformation behaviour of transformative Fe50Mn30Co10Cr10 complex concentrated alloy doped with 0.2 wt % silicon is studied using ex-situ EBSD accompanied with mean and full field crystal plasticity simulations. On silicon doping, martensitic transformation gets suppressed rather nano twinning is observed with tensile deformation. The considerable rise in strength and tensile ductility is attributed to the solid solution strengthening and deformation twinning respectively. Furthermore, crystal plasticity simulations using mean field viscoplastic self-consistent and full field fast Fourier transform FFT approaches are performed to address the texture evolution, the effect of neighbouring grains of different orientations as well as slip and twin activity. Slip is found to be planar in nature which is verified using crystal plasticity simulations. Combination of mean and full field simulations is used to address the effect of neighbouring orientations on the rotation path of individual grains towards the stable end orientation. The critical role of deformation nano twinning in providing extended strain hardening contributing to significant ductility is established. This study highlights the importance of silicon doping in improving the mechanical properties of the Fe50Mn30Co10Cr10 CCA while offering valuable insights into the deformation mechanisms and crystallographic texture evolution.

Simulation of dendritic grain structures with Cellular Automaton–Parabolic Thick Needle model

This article presents advances and computing optimizations on the CAPTN model which couples the Cellular Automaton (CA) and the Parabolic Thick Needle (PTN) methods. This optimized CAPTN model, which is developed in 2D for now, is evaluated on its ability to reproduce two physical quantities developed during directional growth in a constant temperature gradient G with isotherm velocity vL: the interdendritic primary spacing and the grain boundary orientation angle between two grains of different orientations. It is shown that the CAPTN model can reproduce selection between primary branches and creation of new branches from tertiary branches as long as cell size is sufficiently small to model solute interactions between branches. In these conditions, simulations converge toward a distribution of primary branches which depends on the history of the branching events, as has been observed in experimental studies. Average primary spacing obtained tends to decrease with G and vL, in agreement with the theoretical G−bvL−c power law. Contrary to the classical CA model, the grain boundary orientation angle obtained in CAPTN simulations is stable with cell size and in good agreement with previous phase field studies for various gradients. Moreover, the grain boundary orientation angle is found to follow an exponential law with the ratio G/vL.

Surface potential variation across (hk1) and non-(hk1) grain boundaries of antimony triselenide

Electronic materials that can tolerate defects or create self-passivated interfaces expand the horizons to more sustainable electronic devices. Two heuristic models suggest that (i) antimony triselenide is a defect tolerant semiconductor (to certain point defects) and that (ii) the boundaries of grains with a specific orientation are self-passivated. Yet, experimental support or scrutiny of these models is lacking. Partly because measuring a passive quality of a material is perplexing. A possible way forward is to measure defect activity in correlation with other experimental evidence for defect presence, for example, by relating the grain boundaries’ (GBs) nanostructure and electronic quality. One measure of the electronic quality is the magnitude of the surface potential variation across grain boundaries—a high (charged) defect concentration and low defect tolerance typically leads to a significant surface potential variation. On the other hand, direct observation of defects (e.g., by electron microscopy) and a small surface potential variation indicates that the material is defect tolerant. In parallel, a comparison of the surface potential variation across grain boundaries in films with grains of different orientations provides a qualitative measure of the self-passivation of material because only certain crystallographic surfaces are expected to be self-passivated. Herein we report that regardless of the grains’ mutual respective orientation, the grain boundaries of antimony triselenide have a relatively benign electronic quality. This is evident in a shallow surface potential variation across grain boundaries (10–50 mV; 195 GBs were investigated). Yet, a high-resolution TEM investigation reveals that a variety of defects is prevalent at and near the GBs. Additionally, we found that GBs in films with distinct (hk1) orientation indeed have a lower surface potential variation than grains with (hk0) orientation. These findings support both heuristic models and provide a practical way to scrutinize defect tolerance in other polycrystalline semiconductors.

Evaluation of phase and domain switching in Sn-doped BCZT piezoceramics with coexisting ferroelectric phases

Large electrostrain properties are often observed in piezoelectric ceramics for conditions favoring a coexistence of multiple ferroelectric phases. However, the prevalence of different electric-field-induced microscopic mechanisms, viz. phase transition and domain switching, and their relative roles towards macroscopic electrostrain response are not readily understood. Here, we used in situ synchrotron X-ray diffraction and micromechanical modeling to self-consistently describe the electric-field-induced microscopic mechanisms in grains of different orientations in a polycrystalline Pb-free piezoceramic. We reveal, from experimental and modeling results, a unique tetragonal-to-orthorhombic-to-tetragonal phase transformation induced under low electric fields (< 1 kV/mm) in grains with 002 crystallographic poles oriented either within 20° or orthogonal to the applied electric-field direction. In contrast, grains with their 002 poles oriented 30°− 80° to the electric-field direction undergo a continuous tetragonal-to-orthorhombic transformation for electric fields larger than 1 kV/mm. These results emphasize the critical role of a phase-transition-assisted domain switching mechanism in grains of specific orientations towards realizing a large electrostrain coefficient of d33* ∼ 600 pm/V under low electric fields (< 1 kV/mm) in the Pb-free Sn-doped (Ba,Ca)(Zr,Ti)O3 piezoceramic.

Migration of solidification grain boundaries and prediction

Solidification processing is essential to the manufacture of various metal products, including additive manufacturing. Solidification grain boundaries (SGBs) result from the solidification of the last liquid film between two abutting grains of different orientations. They can migrate, but unlike normal GB migration, SGB migration (SGBM) decouples SGBs from solidification microsegregation, further affecting material properties. Here, we first show the salient features of SGBM in magnesium-tin alloys solidified with cooling rates of 8−1690 °C/s. A theoretical model is then developed for SGBM in dilute binary alloys, focusing on the effect of solute type and content, and applied to 10 alloy systems with remarkable agreement. SGMB does not depend on cooling rate or time but relates to grain size. It tends to occur athermally. The findings of this study extend perspectives on solidification grain structure formation and control for improved performance (e.g. hot or liquation cracking during reheating, intergranular corrosion or fracture).

Influence of substructure inhomogeneity on the anisotropy of physical properties of textured materials

Calculation of the physical properties anisotropy is based on single crystal properties and information about material texture, i.e. orientation distribution function (ODF). At the same time, the grains of different orientations are known to have different substructure parameters including the lattice distortion and microstrains. Determination of these parameters is possible with the X-ray method of Generalized Pole Figures (GPF), which consists of registration of the whole X-ray reflection profile under the pole figure recording. As a result, one can obtain the FWHMs of X-ray line profiles and microstrains distributed on the stereographic projection. Despite the observable equilibrium of tensile and compressive microstrains of differently oriented grains within the studied material volume, they can affect the product properties anisotropy. In this study the calculation method for elastic properties and thermal expansion coefficients taking into account substructure inhomogeneity is offered on the basis of elastic energy minimization. Its efficiency is demonstrated for the samples of zirconium alloys.

Effect of Ultra-Fast Heating Before Decarburizing Annealing on Structural Transformations and Properties of Commercial Fe–3% Si Alloy

The effect of ultra-fast (induction) heating of a commercial Fe–3% Si alloy strip (grain oriented electrical steel) at a rate of ~100°С/s on the magnetic properties of finished product is studied in this work. This heating is accomplished after cold rolling followed by recrystallizing decarburizing annealing. It is shown that, in parallel with a reference sample, the ultra-fast heating leads (1) after recrystallizing decarburizing annealing to an increase in the average ferrite grain and, within the near-surface layer, to an increase in the edge component of the {110}〈001〉 texture and decrease in the fraction of {111}〈112〉 component; (2) after the second cold rolling at the final stages of annealing before secondary recrystallization, to an increase in the sharpness of the {110}〈001〉 component; and (3) in the finished product, to a decrease in the average macrograin size by 1.5 times (from ~9 to ~6 mm) and a decrease in the average angle of deviation of easy magnetization axes 〈001〉 from the rolling direction from ~7° to ~6°. The magnetic properties of the studied material exceed those of the comparison metal in all cases. The effect of ultra-fast heating on the texture transformations in the alloy and the formation of the final properties are explained by different nucleation places of grains of different orientations upon primary recrystallization.

Study of substructural heterogeneity of textured materials by the X-ray method of generalized direct pole figures

Any material can be considered a composite consisting of grains of different orientations which possess different properties depending on the history of their reorientation upon thermomechanical processing. A well-known selective character of X-ray methods is attributed to the fact that only grains of certain orientations participate in the formation of reflected radiation. A comprehensive description of the material including information about the substructure of grains of all orientations necessitates developing of the method providing description of the substructural state of grains located in the volume under study by analyzing the profile of x-ray lines. The proposed x-ray diffractometric method of Generalized Direct Pole Figures (GPF) which suggests combination of texture imaging and recording the profile of x-ray lines appeared to be rather efficient in a systematic x-ray study of the substructural heterogeneity of textured metallic materials. The measured parameters of the X-ray line profile — the true angular half-width β and angular peak position 2θ — are determined by the distortion (fragmentation) of the reflecting grains and interplanar spacings in their crystal lattice, respectively. The method provides a possibility to compare the substructure features of grains with different crystallographic orientations. An algorithm for calculation of the true physical half-width of the x-ray line using the necessary computer programs is presented. GPF β and GPF 2θ are presented for metal materials with hcp, fcc, and bcc crystalline lattices, as well as characteristic diagrams of their mutual correlation with texture PF. The use of the developed GPF method makes it possible to identify patterns of the formation of substructural heterogeneity during plastic deformation of metals.

Deformation and fracture of WC grains and grain boundaries in a WC-Co hardmetal during microcantilever bending tests

The deformation and fracture behaviour of constituents of a WC-Co hardmetal were investigated by microcantilever bending technique. The compositions of FIB fabricated microcantilevers were: I) single grains of WC, II) WC grains of different orientations and III) the mixture of WC grains and Co phase. The crystallographic orientation of WC grains and the fracture surface of beams were studied by EBSD and SEM analyses, respectively. It was revealed that the elastic deformation depends mainly on the composition of the beams and the orientation of the WC grains. The Young's modulus of WC grains showed an orientation dependence with decreasing values from the basal (E~800 GPa) towards the prismatic orientations (E~500 GPa), which is in agreement with the theoretical predictions. The deformation behaviour of WC grains exhibited plasticity before their fracture with an average fracture strength of σ = 12.3 ± 3.8 GPa. It was found that the effect of dislocations and nanometre-sized defects (e.g. pores) plays an important role in the bending test of WC grains. Most of the WC/WC boundaries showed brittle failure with an average fracture strength of σ = 4.1 ± 2.5 GPa. It was concluded that the majority of the boundaries in the WC-Co composite are high energy WC/WC boundaries and their fracture strength is generally much lower than that of the WC grains.

Epitaxial Growth of Cu2O on Ag Substrate by Electrodeposition

Cuprous oxide (Cu2O) is a p-type semiconductor with a direct bandgap of 2.1 eV and high hole mobility at ambient temperature. Recently, the importance of using an epitaxial film to fabricate optoelectronic devices to improve the performances has been pointed out [Mahenderkar et al., Science, 355, 1203–1206 (2017)]. Investigation of epitaxial growth of Cu2O on, mostly, MgO substrate by molecular beam epitaxy or pulsed laser deposition has been carried out for a decade. However, these techniques require high-quality substrates and expensive facilities. Electrodeposition, on the other hand, provides another option with ease of operation. However, the substrate has to be electrically conductive and possesses a low lattice mismatch to Cu2O. In this study, the epitaxial growth of Cu2O on Ag substrate by electrodeposition was studied by a combinatorial substrate approach mainly using the electron backscatter diffraction (EBSD) technique. The effect of substrate orientation on epitaxial growth can thus be explored efficiently. The lattice mismatch between Ag and Cu2O is 4.3 %. Prior to the deposition, the annealed, polycrystalline Ag substrate was electropolished and analyzed by EBSD over a marked region of about 500 x 500 μm2. Atomic force microscopy was used to characterize the surface morphology of the substrate grains of different orientations. Afterwards, Cu2O films were deposited galvanostatically on the substrates in an electrolyte containing copper sulfate and lactic acid. The crystal structure and orientation of the marked area was analyzed by EBSD again after electrodeposition. The orientation distribution of the films and the orientation relationship between the overlaid Cu2O and the Ag substrate were thus obtained. X-ray diffraction was also used for phase identification. Results indicated that the substrate grains exhibited similar surface roughness values of approximately 3 nm regardless the orientation. X-ray diffraction reults confirmed that the films deposited at different conditions contained solely the Cu2O phase. No diffraction peaks of Cu and CuO were found. At a low current density of 0.06 mA/cm2, the film has a rough surface composing of faceted islands of 5-20 mm in size. A portion of the islands exhibited the same orientation as the substrate grain. On the other hand, at a high current density of 0.25 mA/cm2, films with smooth surfaces were obtained. The Cu2O films all grew epitaxially on the Ag grains in two orientation relationships: a cube-on-cube one and a <100>/45o one. The origin of the <100>/45o orientation relationship was further studied and will be explained in detail. The deposited films were also analyzed by photoluminescence at room temperature and showed strong near band-edge emissions at 1.97-2.06 eV.

On the effect of grain structure in micro-cutting of polycrystalline aluminate magnesium spinel (PAMS) crystals

This paper studies the anisotropic effect induced by the grain structure of polycrystalline aluminate magnesium spinel (PAMS) on the mechanism of surface generation in the micro-cutting process. The critical depth of cut for ductile–brittle transition (DBT) of PAMS is estimated from 81 to 163 nm by plunge-cutting tests. In the cutting tests with constant cutting depths from 250 nm to 1.5 µm, an apparent regional distribution of crack features is clearly observed and it implies that the randomly oriented crystal grains with different slip systems play an important role in brittle-regime surface generation and fractures evolution. An effective way to obtain a ductile-regime machined surface is to decrease the cutting depth to 50 nm, and a flawless surface can be obtained when the cutting depth is as shallow as 30 nm. With such a low cutting depth, the material is mainly removed by the ploughing effect. Finite element method (FEM) model has been developed to simulate the cutting process crossing a grain boundary of two adjacent grains with different anisotropy material properties. The simulation result supports that the subsurface damage and boundary fractures can be evoked ahead of the actual material removal process by the cutting stress propagating from the precedingly machined grain. Different crack-patterns are shown on the finished surfaces of the two adjacent grains of different orientations.

Bayesian Sequential Design of Experiments for Extraction of Single-Crystal Material Properties from Spherical Indentation Measurements on Polycrystalline Samples

This paper explores a formal strategy for the extraction of single-crystal elastic constants of cubic polycrystalline metals based on the optimal design of spherical indentation experiments. Recent work has formulated the extraction of elastic constants using a two-step protocol. The first step established a surrogate model to capture the dependence of the indentation elastic modulus on the grain (i.e., crystal lattice) orientation and values of single-crystal elastic constants. The second step involved the use of Markov chain Monte Carlo to establish distributions on the elastic constants consistent with experimentally measured indentation moduli in grains of different orientations. The present study refines the second step in order to sequentially identify specific grains that should be indented to provide the most utility in improving the estimated distributions on the elastic constants. The proposed workflow is demonstrated for the extraction of elastic constants for an as-cast cubic polycrystalline Fe-3%-Si sample.

Microstructure evolution under isothermal and continuous cooling conditions via a combined multiphase field and nucleation approach

We demonstrate the microstructure evolution involving the nucleation and grain growth of a binary alloy during the continuous cooling process via a combined multiphase field model and stochastic nucleation computational model. The nuclei are initiated by adding into the total free energy a term of the nucleation energy related to the variables that represents grains of different orientation. Moelans’ interpolation functions are implemented to construct the chemical bulk free energy from coexisting phases/grains for increased stability of multiphase/grain junctions. It was found that the temperature dependent nucleation rate and interface mobility are the main materials properties controlling the features of the resultant microstructures. More even-sized and fine grains can be formed under a high cooling rate given the specified temperature dependent nucleation rate. Solute trapping is the most prominent and solute segregation is the slightest at the highest cooling rate. Equipped with a grain-tracking method, this computational framework provides a viable and computationally efficiently pathway to investigate the large-scale microstructure evolution under various temperature histories that could occur in manufacturing processes.

First‐principles study in an inter‐granular glassy film model of silicon nitride

AbstractBased on a previously constructed intergranular glassy film (IGF) model for bulk silicon nitride, a large periodic model of 3864 atoms containing 2 grains of different orientations from the main bulk β‐Si3N4 and 2 IGFs was fully relaxed using the ab initio density‐functional theory package VASP. The relaxed structure was then used to calculate the electronic structure, density of states, interatomic bonding, partial charge distribution, and electron localization using the OLCAO method. Analysis of the data focuses on the interfacial regions between bulk β‐Si3N4 and the Si‐O‐N glass layer with different orientations. The total bond order density (TBOD) is evaluated in different interfacial and bulk regions. We show minor differences in the internal cohesion between crystalline grains of different facets. However, the overall charges in the bulk crystal grains and in the glassy regions are electropositive which are balanced by the negatively charged interfacial region between the two. The presence of a less rigid glassy layer is the reason for structural flexibility in ceramics without a huge penalty in the steric energy. The optimization of the interfacial structure and bonding via the creation of defective sites is the atomic origin for the existence of the IGF in silicon nitride. The insights obtained from this detailed quantum mechanical analysis of a realistic IGF model are discussed including implications on the strength, fracture toughness, and processing methods. We also discuss the potential applications of our method to other complex materials systems.

An Ex-Situ Study on Epitaxial Growth of Nickel on Copper Substrate in Electrodeposition

An ex-situ method was used to study the anisotropy of the epitaxial growth of electrodeposited nickel on polycrystalline copper substrate. The substrate grain orientation was characterized by electron backscatter diffraction (EBSD) technique prior to the electrodeposition. Nickel films of approximately 1 μm thick were then deposited onto the polished substrates in a sulfamate bath at current densities 2 to 250 mA/cm2. The orientation of the Ni film in the prior-analyzed area was characterized again by EBSD to reveal the orientation relationship between each deposit/substrate pair. EBSD analysis was also carried out for thick deposit from a transverse direction to clarify the growth behavior and microstructural evolution on grains of different orientations. Results indicated that epitaxial growth was allowed solely on grains having an orientation of <100>//ND at 2 mA/cm2. On the contrary, nickel deposits grew epitaxially on all grains no matter the orientation as the current density was in a range of 10-100 A/cm2. However, the surfaces of the non-(100) oriented epilayers became rough with increasing thickness and finally they were covered by fine nuclei formed via a twin-mediated nucleation process.

An Ex-Situ Study of Epitaxial Growth of Nickle on Copper Substrate in Electrodeposition

An ex-situ method was used to study the anisotropy of the epitaxial growth of electrodeposited nickel on polycrystalline copper substrate. The orientation of the substrate grain was characterized by electron backscatter diffraction (EBSD) technique prior to the electrodeposition. Nickel films of approximately 1 um thick were then deposited onto the polished substrates in a sulfamate bath under various current densities. The orientation of the Ni deposits located in the prior-analyzed area was characterized again by EBSD to reveal the orientation relationship between the deposit and the substrate. EBSD analysis was also carried out for thick deposits from a transverse direction to clarify the growth behavior and microstructural evolution of the deposits on grains of different orientations. Results indicate that epitaxial growth is allowed solely on grains having an orientation of <100>//ND at a low current density. On the contrary, the nickel deposits grow epitaxially on almost all grains no matter the orientation as the current density is in a range of 1-10 A/dm2. However, the surface topology of the deposits on substrate grains of different orientations is very different. Accordingly, the microstructure evolution of the <100>//ND and non-<100>//ND deposits are very different and detail will be presented.

Prediction of viscous cracking and cyclic fatigue of salt polycrystals using a joint-enriched finite element model

We present a new Joint-enriched Finite Element Method (JFEM) to predict viscous damage and fatigue in halite polycrystals in 2D. Different visco-plastic finite elements are used to represent grains of different orientations, and joint elements are used for modeling crack propagation. Simulations of uniaxial creep tests show that, as it could be predicted theoretically, viscous shear deformation in grains causes geometric incompatibilities. Numerical results also show that the transition between secondary and tertiary creep corresponds to inter-granular crack coalescence. The JFEM model captures the mechanical behavior of halite under cyclic loading, mainly: (a) Higher stress amplitude, lower confining stress, and lower loading frequency increase deformation and damage; (b) The polycrystal’s Young’s modulus decreases exponentially with the number of cycles; (c) The behavior is similar for different loading directions. Simulations with intra- and inter- granular joint elements show that most stress concentrations occur in intra-granular joints where several angular grains are in contact. Results of creep tests obtained with the JFEM are compared to those obtained with an inclusion-matrix model that accounts for damage accommodation due to grain breakage. Both the JFEM and inclusion-matrix models are calibrated against experimental creep tests to: (a) Produce a Young’s modulus of 23 GPa for the polycrystal; (b) Match secondary creep strain rates; (c) Match the time of tertiary creep initiation. In the inclusion-matrix model, the absence of grain geometric rearrangement results in a brutal failure just after the first grain breakage that triggers tertiary creep. Moreover, the JFEM model highlights the development of crack patterns upon viscous deformation. The JFEM is of great promise to understand complex phenomena of viscous accommodation coupled with grain interface debonding.

Microstructure and surface morphology of thin AlN films formed on sapphire by dual magnetron sputtering

Results of studies of the effect of the discharge current on the crystalline structure, surface morphology, and thickness of thin AlN coatings deposited by reactive dual magnetron sputtering on c-axis oriented sapphire wafers have been described. Using grazing incidence X-ray diffraction, it has been determined that the coatings have a wurtzite crystalline structure and at least two types of grains with different orientations of the (002) planes. Electron microscopy has revealed that the coatings are composed of vertically aligned columnar grains and a nucleation layer. The grains are uniformly distributed over the substrate surface; each of the grains consists of smaller crystallites. It has been found that the discharge current largely affects the concentration of grains of different orientations and has hardly any effect on the size of the nuclei.

Crystallographic Orientation Determination of Hexagonal Structure Crystals by Laser Ultrasonic Technique

Spatially resolved acoustic spectroscopy (SRAS) is a laser ultrasonic technique that shows qualitative contrast between grains of different orientation, illustrating the sensitivity of acoustic waves to the material structure. The technique has been improved significantly on determining the full orientation of multigrain cubic metals, by comparing the measured surface acoustic wave (SAW) velocity to a pre-calculated model.In this paper we demonstrate the ability of this technique to determine the orientation of hexagonal structure crystals, such as magnesium and titanium based alloys. Because of the isotropy of the SAW velocity on the basal plane (0001) of hexagonal crystals, the slowness surface is shown as a circle. As the plane moves from (0001) towards (112̄0) or towards (101̄0), the slowness surface gradually turns into an oval. These acoustic properties increase the difficulty in orientation determination.The orientation results of a grade 1 commercially pure titanium by SRAS is presented, with comparison with electron backscattered diffraction (EBSD) results. Due to the nature of SAWs on hexagonal structure crystals, only the results of Euler angles 1 and 2 are discussed. The error between SRAS and EBSD is also investigated.