Crystallographic Orientation Relationship Research Articles

Designing eutectic medium-entropy alloys CoFeNiTax with outstanding mechanical properties

The eutectic medium-entropy alloys CoFeNiTax (x = 0.4, 0.5, 0.6) were designed successfully based on binary eutectic systems and thermodynamics calculations in this study. With the increase of Ta content, the solidified microstructures evolved from hypoeutectic to full eutectic and finally to hypereutectic. The primary phases in the hypoeutectic and hypereutectic were FCC solid solution and C14-Laves phase, respectively. The solidified microstructures were coarsened and spheroidized by the heat treatment, and a high-density of needle-like Laves phase precipitated in the FCC phase of the CoFeNiTa0.4. The crystallographic orientation relationship between the precipitated phase and matrix phase was [2‾ 42‾ 3]Laves//[011]FCC, and the crystal plane (1 1‾ 1)FCC was almost parallel to (0 1‾ 12)Laves, just with a mismatch angle of about 6°. The compressive strength and fracture strain of the heat-treated alloys were within 2232∼2465 MPa and 22.5–32.8 %, respectively, being superior to most high-entropy alloys. The excellent combination of strength and toughness was attributed to the synergistic effects of various strengthening-toughening mechanisms, including the second-phase strengthening, the solid solution strengthening, the interface strengthening and toughening, and the twinning toughening.

Precipitation evolution of M5B3 boride in diffusion affected zone and its effect on mechanical properties of TLP bonded Mar-M247 superalloys

Boron is usually added in the bonding interlayer as the melting point depressant element in the transient liquid phase (TLP) bonding of Ni-based superalloys, which inevitably leads to the precipitation of borides and therefore has an important impact on the mechanical properties of the joints. M5B3-type borides (where M is a mixture of Cr, W and Mo) are the predominant borides in diffusion affected zone (DAZ) of the Mar-M247 bonded joints. In present work, the precipitation and evolution of M5B3 in the joints with different bonding time have been systematically investigated by multi-scale methods. Three kinds of crystallographic orientation relationships between M5B3 and matrix have been observed, and the morphologies and precipitation positions of M5B3 borides are found to have certain characteristics in specific bonding time joints. These crystallographic orientation relationships are consistent with the predictions based on calculations of coincidence of reciprocal lattice points (CRLP) model. The effect of the precipitation of borides on mechanical properties has been evaluated by means of microhardness and micropillar compression testing.

Rock-salt Ti1−xO → rutile TiO2−x transformation twinning via pulsed laser deposition – implications for the dense (hkl)-specific phase change and optoelectronic properties

The R + r intimate intergrowth was found to form a butterfly twin following the optimum crystallographic orientation relationship [101]R//[111̄]r by the close-packed (1̄11)R and (011)r planes as the twin boundary and phase interface, respectively.

Preparation and hydrogen diffusion evaluation of the yttrium oxide dispersed tungsten matrix for use in nuclear thermal propulsion

The fissile fuel loss in tungsten (W) based ceramic-metal (Cermet) element used in nuclear thermal propulsion is of great importance. In this study, the W-Y2O3 composite matrix was manufactured tentatively by Spark Plasma Sintering (SPS) to relieve the fuel loss. Performance evaluation of hydrogen (H2) permeation and diffusion behaviors in the matrix was carried out by a gas permeation device. The results indicate that the diffusion coefficient of H2 in the pure W matrix is nearly 10 times larger than that in the W-Y2O3 matrix at a test temperature of 823 K. Based on the results, a careful investigation of the fuel loss mechanism of the Y2O3 dispersed W matrix was performed. SEM and TEM showed that the fine Y2O3 particles are distributed along grain boundaries of the W ternary-phase and present a distinct transition region of about 10 nm between the Y2O3 and W phases. In particular, the crystallographic orientation relationship suggests that a semi-coherent structure is formed at the W/Y2O3 phase interface: (0 1 −1) W || (1 0 −1) Y2O3 and [0 1 1] W || [1 1 1] Y2O3. This semi-coherent structure is favorable for binding the two phases together tightly, thus hindering the inward diffusion of H2 greatly. Moreover, the improved density and refined size of the W grains are achieved. Therefore, there is no doubt that the dispersion of Y2O3 is beneficial for lowering the H2 diffusion rate in the W matrix and thus reducing the fuel loss effectively. This work furthers our understanding of the key role of Y2O3 in the W matrix used in nuclear thermal propulsion.

Crystallographic Orientation and Strain in GaN Crystals Grown on 6H-SiC and Sapphire Substrates

The crystallographic-orientation relationship between GaN crystals grown via hydride vapor phase epitaxy (HVPE) on 6H-SiC was investigated. This study employed electron backscatter diffraction (EBSD) Kikuchi diffraction patterns and pole figures to identify this relationship and calculate lattice mismatches. Comparing the misorientation of GaN crystals on different substrates along the growth direction using EBSD mapping, we identify the strain in GaN based on crystallographic-orientation results. Raman spectroscopy results correlate residual stress in GaN with lattice mismatches, aligning with our previous works. Residual stress of GaN on different substrates identified using PL spectrum also confirmed these results. The HRXRD characterized the dislocation density of GaN crystals grown on these substrates.

Elucidating deformation pathways and interface characteristic of self-accommodated dual γ/ε phase microstructure in Fe–Mn–Si–Al alloy

There has been an intense scientific interest in investigating the phenomenon of deformation-induced ε-ε martensite (hcp) interaction owing to the thermodynamically paradoxical reverse transformation and mechanical twinning. In this study, detailed transmission electron microscopy has been employed to examine the crystallographic orientation relationship, phase stability and boundaries between the intersection phases on the ε-ε intersections in a 10% tensile deformed Fe–30Mn–4Si–2Al alloy. The transformation/twinning scheme is systematically summarized initiating from the austenite matrix (γ) and two deformation-induced ε-martensite variants. It involves diverse intersection reactions: mechanical ε-twins, a 90°-rotating γ-phase from the γ matrix (γR), and 90°-rotate ε-phase re-transformed from the intersection γ. All these phases share a common 〈101〉γ || <21¯1¯0>ε axis that is equivalent to the intersection axis of the crossing {111}<12¯1>γ shears and interrelated with rotational angles with respect to the axis. Electron diffraction, coupled with stereographic analysis, revealed the distinct orientation relationships between γ–ε and γR–ε phases. The boundaries between the intersection γR and neighboring ε-phase are inclined from the corresponding {111}γ||{101¯1}ε planes. By means of the phenomenological theory of martensite crystallography (PTMC), the inclination of the boundary is rationalized by considering the lattice-invariant shear on the double {111}γ plane inside the intersection γ to satisfy the invariant plane condition of the boundary.

Unveiling interface structure and polarity of wurtzite ZnO film epitaxially grown on a-plane sapphire substrate

Atomic-scale structure properties of the epitaxial growth of the wurtzite ZnO film prepared on an a-plane sapphire (α-Al2O3) substrate have been investigated by using aberration-corrected transmission electron microscopy. The crystallographic orientation relationship of (0001)[1¯1¯20]ZnO//(112¯0)[0001]α-Al2O3 has been determined between the ZnO film and the α-Al2O3 substrate. Two types of oxygen-terminated a-plane α-Al2O3 substrate surfaces have been characterized, which leads to the formation of different heterointerface structures and ZnO domains with opposite lattice polarity. The coalescence of opposite polarity domains results in the appearance of inversion domain boundaries (IDBs) on prismatic planes, and kinks occur on basal planes during the propagation of IDBs within the film. Additionally, the structure of stacking mismatch boundaries in the film with threefold coordinated Zn and O atoms has been resolved. We believe that these findings can be helpful to advance the understanding of the complex propagation of planar defects (e.g., IDBs and stacking faults) in wurtzite films and the interface structure and polarity of wurtzite films on the a-plane sapphire substrate.

Nucleation of recrystallization

This paper reviews the mechanisms of nucleation during recrystallization of cold deformed, single phase polycrystalline metals including metals with large particles. The classic nucleation theories and conceptions are shortly summarized, while the main focus is on our results from recent 3D studies of nucleation. The novel results are related to the classic nucleation ideas and agreement/disagreement as well as new suggestions are discussed. More specifically the paper covers recovery leading to intragranular nucleation, bulge nucleation (which is often referred to as strain induced boundary migration), and particle stimulated nucleation. Also, effects of clustered nucleation, crystallographic orientation relationships and residual stress are considered. Finally future studies are suggested, which we consider key to advancing the understanding of nucleation during recrystallization.

Flash healing of Vickers microcracks formed on the (001) surface of cubic zirconia single crystals

Flash healing, a technique for microcrack healing using a flash event, has recently attracted attention for effective microcrack healing of ceramics. To investigate the diffusion-accelerated phenomena that occur during flash healing, the flash-healing behavior of Vickers indentation microcracks on (001) zirconia single crystals was investigated, mainly from the viewpoint of microstructure analysis of the healed microcracks. Scanning electron microscopy and atomic force microscopy showed that the surface microcracks were rapidly healed. However, scanning transmission electron microscopy showed that a row of pores remained along the original microcrack inside the crystal, and the crystallographic orientation relationship on both sides of the microcrack was restored to that of the original single crystal. Compared with the findings for healing without an electric field, the distance from the pore closest to the surface was larger and the total pore volume was smaller for flash healing. These results suggest that flash treatment increases lattice diffusion.

Effect of a novel controlled thermomechanical treatment on the microstructure and mechanical properties of a high-carbon nanobainitic steel

The effect of the novel controlled thermomechanical treatment, including torsion components in the elastic strain range during the isothermal holding on the microstructure and mechanical properties of the high-carbon nanobainitic steel, was investigated. TEM observations of the thermo-mechanically treated steel revealed bainitic ferrite laths with an average size of 68 ± 40 nm and films of retained austenite with an average size of 34 ± 17 nm, along with the blocky morphology of retained austenite in sub-micron scale. The XRD synchrotron diffraction allows estimating the amount of retained austenite at 43.1 ± 1.2% volume fraction with a carbon concentration of 1.17 ± 0.09 wt.%. Furthermore, the deconvolution of (200) Fe-γ reflections corresponding to two different low-carbon and high-carbon retained austenite peaks and, simultaneously, the blocky and film-like retained austenite was performed. In addition, the Nishiyama–Wassermann (N–W) crystallographic orientation relationship between bainitic ferrite and retained austenite was described as dominant using the misorientation distribution function (MDF). The crystallographic texture results indicated that the main growth of bainitic ferrite plates occurred after removing external stress during isothermal holding. The tensile tests and hardness measurements showed a high tensile strength achieved mainly by nano-metric bainitic ferrite plates and a high dislocation density. The high level of elongation is most likely attained due to a high amount of retained austenite in steel and both TRIP and TWIP effects during tensile deformation.

Formation mechanism of composite secondary phase particles in a solution-treated Si-modified Zircaloy-4

Zr-Si binary precipitates affect mechanical and corrosion properties of Si-modified Zircaloy-4. In this study, composite secondary phase precipitates, having a core of C16 Zr2Si precipitate semi-coated with C15 Zr(Fe,Cr)2 Laves phase, were analysed as observed after solution treatment of experimental Si-modified Zircaloy-4. Crystallographic orientation relationship between the body-centred tetragonal (BCT) Zr2Si and face-centred cubic (FCC) Zr(Fe,Cr)2 Laves phase regions was determined to be (101¯)C16 // (110)C15 and [11¯1]C16 // [11¯1]C15. Two regions formed an incoherent interface accommodating about 30 % misfit strain, calculated by Bramfitt two-dimensional lattice mismatch criterion. The mechanism of formation of composite precipitates was described which, in turn, outlines the way for manipulating microstructure of composite precipitates to further optimise mechanical properties of Si-modified Zircaloy-4.

A novel approach to prepare high density SiC ceramics by powder extrusion printing (PEP) combined with one-step sintering method

High density (97 %) SiC ceramics containing in-situ synthesized Y4Al2O9 (YAM) have been successfully fabricated by a novel PEP additive manufacturing technology combined with a one-step sintering method without any post-treatments. The process of additively manufacturing SiC green body, debinding and sintering has systematically studied. Meanwhile, the atomic structure of SiC and YAM was characterized, and the mechanical properties of sintered SiC ceramics were measured. The HRTEM results revealed the crystallographic orientation relationships between YAM and SiC as (0 4 0) YAM // (1 0 1- 1) SiC and [1 0 2] YAM // [1 2¯ 1 0] SiC for the first time. The density, Vickers hardness and three-point bending strength of the sintered SiC samples are 3.11 g/cm3, 19.35 ± 0.28 GPa and 225 ± 27 MPa, respectively. Thus, PEP combined with the one-step sintering method provides a new strategy for complex-shaped SiC ceramics with high density and mechanical properties.

Enhancing strength-ductility synergy of graphene/Al–Cu–Mg composites via forming MgAl2O4@graphene complex structure

The strength and ductility of graphene nanoplate (GNP) reinforced 2009Al composite (GNP/2009Al) were enhanced simultaneously, through wrapping MgAl2O4 around GNP and forming an MgAl2O4@GNP complex structure via in-situ reaction of CuO, Al and Mg during fabrication. This architecture generated numerous Al–MgAl2O4-GNP complex interfaces due to crystallographic orientation relationship of the Al–MgAl2O4 interface and the strong Al–O–C chemical bond, therefore, it not only enhances the load transfer efficiency of GNP but also improves the dislocation storage capacity of the Al matrix. These factors contributed to a stable and persistent working hardening capability for the GNP/2009Al composite. The feasible design proposed in this work, namely the in-situ Al–MgAl2O4-GNP complex strategy, can achieve improved tensile properties in GNP/2009Al composites.

Insight into tuning of ZrO2 distribution and mechanical properties of directionally solidified Al2O3/(5Re0.2)AG/ZrO2 eutectic ceramic composites

A novel Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12((5Re0.2)AG)/ZrO2 eutectic high entropy oxide ceramic composite (HEOC) was prepared by the directional solidification technique. The Al2O3/(5Re0.2)AG/ZrO2 eutectic HEOCs had a refined microstructure and different crystallographic orientation relationships of <10-10>Al2O3 || <103>(5Re0.2)AG || <100>ZrO2, {11–20}Al2O3 || {100}(5Re0.2)AG || {100}ZrO2, {0001}Al2O3 || {103}(5Re0.2)AG || {100}ZrO2 compared to Al2O3/YAG/ZrO2 eutectic ceramic composites. ZrO2 was distributed more uniformly and dispersedly in Al2O3/(5Re0.2)AG/ZrO2 eutectic HEOCs than in Al2O3/YAG/ZrO2 due to the similar volume strain of Al2O3/(5Re0.2)AG, (5Re0.2)AG/ZrO2 and Al2O3/ZrO2. As a result, mechanical performance including hardness, elastic modulus, and fracture toughness had been greatly improved because of the refined microstructure, tailored interfacial structure, and homogeneous distribution of ZrO2 caused by the introduction of the high entropy (5Re0.2)AG.

NiO thin film with an extremely high index (7 overline{1 } 4) on r-plane sapphire substrate

Thin film epitaxy is essential for state-of-the-art semiconductor applications. The combination of different substrates and deposition methods leads to various crystallographic orientation relationships between thin films and substrates, which have a decisive impact on thin film performance. By utilizing pulsed laser deposition, we discovered a very high-index (7 overline{1 } 4)–oriented NiO thin film when deposited on r-plane text{(10}overline{1}text{2)} sapphire substrates. The in-plane epitaxial relations are {[13overline{1 }]}_{text{NiO}}text{||[1}overline {2}{text{10]}}_{text{Sapphire}} and {[overline{1 }12]}_{text{NiO}}text{||[10}overline{11}{text{]}}_{text{Sapphire}}, and the lattice mismatch is 3.2% and 0.4% along two directions, respectively. Exchange bias studies by the deposition of Co on NiO (111) and NiO (7 overline{1 } 4) show different behaviors, which may be associated with the spin density and alignment on the surface.Graphical abstract

Martensitic transformation pathways and crystallographic orientation relationships in steel

Martensite is one of the most important structures determining the ability to tailor the performance of steel and several other engineering materials. In previous studies, the face-centered cubic (FCC) to hexagonal close-packed (HCP) (or body-centered cubic (BCC)) martensitic transformation and the FCC to body-centered tetragonal (BCT) (or BCC) martensitic transformation during deformation and quenching were widely investigated; these transformations usually improve the plasticity and strength of steel, respectively. In this work, detailed transmission electron microscopy (TEM) observations and electron diffraction pattern analyses of the BCT and BCC twins are performed along the [110], [131], and [1¯53] zone axes. The transformation of BCT twins into BCC twins along the [131] zone axis is also analyzed through in situ heating during the TEM observations. The high-resolution TEM observations of mutually perpendicular BCT variants are consistent with the atomic arrangement obtained for the quenching pathway during the martensitic transformation. In addition, different orientation relationships between austenite and martensite are explained in terms of the atomic migration occurring during the deformation pathway and the quenching pathway of the martensitic transformation.

Friction stir processing: An effective thermo-mechanical processing technique for carbon steels

This review paper deals with the detailed study of published research work on FSW/FSP of different types of steels and post processing such as heat treatment effects on additively manufactured steel beads. In this context, it comprises of post processing effects on steel beads fabricated by additive manufacturing technique that includes different techniques like selective laser melting (SLM), Laser-TIG (Tungsten inert gas), Metal inert gas welding, etc. along with post processing techniques such as hot iso-static pressing (HIP), conventional heat treatment (HT), post weld heat treatment (PWHT), etc. Also, it consists of the pros and cons of FSW/ FSP, especially on low and medium carbon steels. Moreover, this paper is mainly related to the effects of friction stir welding/ processing on the evolution of microstructure, weld morphology, and temperature gradients in the processed region. In addition, there are detailed analyses of tool selection, effect of weld pitch ratio, effect of carbon content (Wt. %), and hard phase volume fraction on yield strength i.e. carbide distribution in the FSP low and medium carbon steels, and their correlation with the mechanical responses as well as crystallographic orientation relationship. Finally, based on published research, gaps are highlighted and presented as future scope of research work.

Role of scanning speed on the microstructure and mechanical properties of additively manufactured Al2O3‒ZrO2

AbstractMelt‐grown Al2O3–ZrO2 eutectic (AZ eutectic) ceramics have attracted extensive attention for harsh environment applications. In this work, AZ eutectic ceramic is additively manufactured via one‐step laser powder bed fusion (LPBF). The role of scanning speed on phase formation, crystallographic characteristics, microstructure evolution, and mechanical properties were systematically investigated. The as‐fabricated specimens are mainly composed of α‐Al2O3 and t‐ZrO2. Lower scanning speeds induced the formation of cellular structures consisting of randomly oriented ZrO2. In contrast, nanometer eutectic lamellar structure with well‐defined multiple crystallographic orientation relationships, for example, {100} Al2O3 || {100} ZrO2 and {0001} Al2O3 || {001} ZrO2, occurred at higher scanning speeds. Both the cell size and lamellar spacing decreased with increasing scanning speed. With the microstructure refinement, the crack propagation mode changes from intergranular to transgranular fracture, leading to progressively enhanced fracture toughness with a maximum value of 7.76 MPa·m1/2. The present work could shed light on tailoring the microstructure of LPBF AZ eutectic ceramic via varying processing parameters.

Twinning microstructure in the solid-phase epitaxial crystallization of BaTiO3

Amorphous BaTiO3 layers deposited on SrTiO3 (001) substrates at room temperature were subsequently crystallized using solid phase epitaxy (SPE). Heating an initially amorphous BaTiO3 layer in air at 650 °C for 3 h resulted in crystallization with components in two distinct crystallographic orientation relationships with respect to the substrate. Part of the volume of the BaTiO3 layer crystallized in a cube-on-cube relationship with the substrate. Other volumes crystallized in four variants of a 70.5° rotation about ⟨110⟩, resulting in a ⟨221⟩ surface normal in each case. Each of these four variants forms a Σ = 3 coincident site lattice with respect to the SrTiO3 substrate and the cube-on-cube oriented BaTiO3. Heating for the same duration and temperature in a reducing gas atmosphere resulted in the formation of polycrystalline BaTiO3 with no preferred crystallographic orientation. The dependence on the gas atmosphere indicates that it may be possible to tune the annealing time, temperature, and atmosphere to produce a single crystalline BTO on STO by SPE or produce a desired distribution of orientations.

Relationship between β→α dynamic transformation and dynamic recrystallization under thermomechanical coupling in Ti-5Al-5Mo-5V-1Cr-1Fe alloy

The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were performed within the range of deformation temperatures of 710–860 °C and strain rates of 0.001–1 s–1. Based on electron backscatter diffraction (EBSD) characterization and analysis technology, the interaction between dynamic phase transformation (DPT) of β-to-α and dynamic recrystallization (DRX) under thermal-mechanical coupling is deeply and systematically explored. We clarify the effects of temperatures and strain rates on the orientation relationship during dynamic precipitation of α-phase within β grain interiors possessing special orientation. The results show that the intragranular α-phase precipitated on the subgrain boundaries near {001}β with a high degree of dynamic recovery (DRV) deviates more from Burgers Orientation Relationship (BOR) than the α-phase that precipitates near {111}β as temperature increases. The proportion of α-phase precipitated by strain-induced on β recrystallized equiaxed grains for the deviating angle from BOR (θBOR) in the range of 20°–30° increases to 40% with the increase of strain rates below 800 °C. In addition, the α-phase is dynamically precipitated on the grain boundaries with {110}β orientation, which undergoes continuous dynamic recrystallization (CDRX), exhibiting epitaxial recrystallization, namely {110}β//{0001}α. Furthermore, the morphology of grain boundaries α phase (αGBs) precipitated by strain-induced phase transformation (SIPT) on specific types of β grain boundaries (βGBs), as well as the crystallographic orientation relationship and variant selection effect between adjacent α-variant within β grains are elucidated. The orientation relationships between α variants in {111}β grain are related with each other by 50°–60°/<–12–10> and 60°–70°/<–48–43> rotation. The “necklace” αGBs of recrystallization exhibit mainly the rotation of 50°–70° around the 〈2–310〉 zone axis, while the adjacent α-variant in the grain interiors is mainly 60° or 90°/<12−30>. In summary, the study has contributed to a deeper understanding of the deformation behavior and DPT laws of β-to-αp in near-β titanium alloy, which lays a foundation for the optimization of the hot deformation process and mechanical properties.