Crystallographic Orientation Relationship Research Articles

Investigation on the crystallographic orientation relationships and interface atomic structures in an in-situ Ti2AlN/TiAl composite

In this research work, 15vol% Ti2AlN particles reinforced TiAl alloy matrix composite was prepared by an in-situ reactive hot processing method using Ti, Al and TiN powders as raw materials. Transmission electron microscope (TEM) coupled with energy-dispersive spectroscopy (EDS) was utilized to investigate the morphology characteristics of Ti2AlN particles. The crystallographic orientation relationships and interface atomic structures between various shaped Ti2AlN particles and TiAl matrix were investigated by the means of selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). The results show that four kinds of Ti2AlN particles presented in the composite, which include vast majority of elliptical and polygonal Ti2AlN particles with the sizes of 4μm, few hexagonal Ti2AlN particles with the sizes of 4μm and small plate Ti2AlN particles with the sizes of 0.4μm. The elliptical and polygonal Ti2AlN particles have no fixed crystallographic orientation relationship with TiAl matrix, the elliptical and polygonal Ti2AlN/TiAl interfaces are incoherent interphase boundaries composed by many atomic-scale microfacets. The hexagonal and small plate Ti2AlN particles have a fixed orientation relationship with TiAl matrix. Both the hexagonal and small plate Ti2AlN particles have a ledge and terrace coherent interface with TiAl matrix.

Intergrowth of C phase within μ phase in a Re-containing Ni-base single crystal superalloy

Precipitation of topologically close-packed phases in a Re-containing Ni-base single crystal superalloy was studied under elevated temperature by in situ transmission electron microscopy. Above 1150°C, a new intergrowth structure called C phase was found within μ phase with a defined crystallographic orientation relationship. Elements mapping analysis reveals that C phase has a similar element composition as μ phase, but contains a lower level of Cr, W and Re. With increasing temperature, the proportion of C phase increases gradually. At 1250°C, C phase becomes the dominant precipitate. It is demonstrated that C phase is more thermodynamically stable than μ phase above 1150°C that leads to an intergrowth pathway from μ phase to C phase.

Microstructure and coercivity in La-coated Nd2Fe14B thin films

We investigated La-coated Nd2Fe14B thin film magnets by scanning/transmission electron microscopy to clarify the coercivity enhancement mechanism in Nd-Fe-B permanent magnets. The coercivity of La-coated film magnets was increased from 8.5 to 15 kOe by post-annealing. The fcc-LaOx layer was epitaxially grown on [001]-oriented Nd2Fe14B fine grains with a crystallographic orientation relation of Nd2Fe14B (001)[110] || LaOx (111)[112¯], both in the as-deposited and post-annealed films. STEM-EDS elemental analysis revealed that the only difference caused by post-annealing was the O content in the LaOx layer, which increased from 15 to 35 at.%. These results suggest that the magnetocrystalline anisotropy of the Nd ions, which were reduced at the surface of Nd2Fe14B, would be recovered by the presence of O, leading to a remarkable increase in the coercivity.

Crystallographic orientations of intermetallic compounds of a multi-pass friction stir processed Al/Mg composite materials

The crystallographic orientation relationships between intermetallic compounds and matrices were investigated in the interface of an overlapped multi-pass friction stir processed Al/Mg composite materials. During the friction stir processing, an Mg rich intermetallic compound (γ-Al12Mg17) was formed close to the bottom Mg alloy and an Al rich intermetallic compound (β-Al3Mg2) was formed close to the top Al alloy. Two new orientation relationships between the Mg matrix and the γ-Al12Mg17 were observed and analyzed. One was identified as 011¯2Mg//1¯01γ, 01¯11Mg//(101)γ, and the other one was identified as 12¯10Mg//[531]γ, (0001)Mg 1.7° form 1¯21¯γ. The stereographic projections of two new orientation relationships were calculated and discussed. Moreover, high resolution transmission electron microscopy studies of the interface between the Mg matrix and the γ-Al12Mg17 indicated that the γ-Al12Mg17 had a coherent interface with the Mg matrix. It was also observed that the β-Al3Mg2 had a cubic-to-cubic orientation relationship with the Al matrix in the Al/Mg composite material interface.

Orientation Relations of Martensitic Transformations in FeMnCr Steels

The crystallographic orientation relations of phases forming during the martensitic transformation determine the properties of alloys. In TRIP/TWIP steels, the circumstances of thermomechanical treatment (e.g. temperature, deformation) define the forming of martensites of different origins. Due to the thermomechanical treatment, thermally induced martensite (εTH), strain induced martensite (εD) and α’ martensite phases are present in the samples besides the austenite. The proportion of martensites in the sample is defined by the parameters of treatment. The thermally and strain induced martensites which are simultaneously present in the alloy at room temperature can be differentiated by the orientation relations.The martensitic transformations were followed by different methods in FeMn alloys with different Cr content. The macroscopic crystallographic anisotropy was measured by X-ray diffraction method; the microscopic one was examined by EBSD. The cognition of phenomenon observed in the texture image in different scales helps determine the possible origin of martensites.

In-situ synthesis, microstructure and properties of Ti2AlN/TiB2 composite

Abstract Dense Ti2AlN/TiB2 composite was successfully fabricated via in-situ hot pressing using Ti, Al, and BN powders as starting materials. The reaction path, microstructure and typical properties were systematically investigated. It was found that the crystallographic orientation relationship between Ti2AlN and TiB2 could be expressed as: (0 0 0 1) Ti2AlN//(0 0 0 1) TiB2 and [1 2 ¯ $\bar 2$ 1 0] Ti2AlN//[1 2 ¯ $\bar 2$ 1 0] TiB2 for the first time. The composite exhibits high flexural strength (924 ± 45 MPa), high hardness (13.4 ± 0.3 GPa) and high electrical conductivity (6.5 ± 0.2 × 106 (Ω m)−1).

Microstructural constraints on the mechanisms of the transformation to reidite in naturally shocked zircon

Zircon (ZrSiO4) is used to study impact structures because it responds to shock loading and unloading in unique, crystallographically controlled manners. One such phenomenon is the transformation of zircon to the high-pressure polymorph, reidite. This study quantifies the geometric and crystallographic orientation relationships between these two phases using naturally shocked zircon grains. Reidite has been characterized in 32 shocked zircon grains (shocked to stages II and III) using a combination of electron backscatter diffraction (EBSD) and focused ion beam cross-sectional imaging techniques. The zircon-bearing clasts were obtained from within suevite breccia from the Nordlingen 1973 borehole, close to the center of the 14.4 Ma Ries impact crater, in Bavaria, Germany. We have determined that multiple sets (up to 4) of reidite lamellae can form in a variety of non-rational habit planes within the parent zircon. However, EBSD mapping demonstrates that all occurrences of lamellar reidite have a consistent interphase misorientation relationship with the host zircon that is characterized by an approximate alignment of a {100}zircon with a {112}reidite and alignment of a {112}zircon with a conjugate {112}reidite. Given the tetragonal symmetry of zircon and reidite, we predict that there are eight possible variants of this interphase relationship for reidite transformation within a single zircon grain. Furthermore, laser Raman mapping of one reidite-bearing grain shows that moderate metamictization can inhibit reidite formation, thereby highlighting that the transformation is controlled by zircon crystallinity. In addition to lamellar reidite, submicrometer-scale granules of reidite were observed in one zircon. The majority of reidite granules have a topotaxial alignment that is similar to the lamellar reidite, with some additional orientation dispersion. We confirm that lamellar reidite likely forms via a deviatoric transformation mechanism in highly crystalline zircon, whereas granular reidite forms via a reconstructive transformation from low-crystallinity ZrSiO4 within the reidite stability field. The results of this study further refine the formation mechanisms and conditions of reidite transformation in naturally shocked zircon.

Ga-polar GaN film grown by MOVPE on cleaved ScAlMgO4(0001) substrate with millimeter-scale wide terraces

Cleaved ScAlMgO4 (SCAM) substrates with small lattice mismatch of 1.8% to GaN were used for metalorganic vapor phase epitaxial (MOVPE) growth of GaN. A single crystalline GaN film with a flat surface was obtained on a cleaved substrate without peeling off of the film, which is contrast to the growth on ZnO substrate with comparably small lattice mismatch to GaN. Polarity of the film was proven to be Ga polarity and an interface model was proposed based on the topmost surface structure of the cleaved SCAM. The effect of substrate-cleaning and growth conditions on the surface morphology, crystallographic orientation relationship with the substrate, threading dislocation densities, small residual strains, and small background carrier density of GaN have been studied. To discuss the residual strains, thermal expansion coefficient of SCAM has also been measured.

Formation and Dissolution of Hydride Precipitates in Zirconium Alloys: Crystallographic Orientation Relationships and Stability after Temperature Cycling

Hydride precipitation due to the spontaneous and fast hydrogen diffusion is often pointed as causing embrittlement and rupture in zirconium alloys used in the nuclear industry. Transmission Electron Microscopy (TEM) and X-Rays Diffraction (XRD) have been used to study the precipitation of hydride phases in zirconium alloys as a function of the hydrogen content. The orientation relationships observed between the hydride phase and the substrate were similar to those previously observed in Titanium hydrides grown on Titanium. Dislocation emission from the hydride precipitates has been directly related to the relaxation of the misfit stresses appearing during the transformation. The stability of the hydride phases after several dissolution-reprecipitation cycles have been studied by DSC, TEM and XRD for different total hydrogen content in several alloys. The energy of precipitation observed is lower than that of the dissolution in each case studied. The temperature associated with these two processes slightly increase as a function of the cycle number, as a result of the homogenizing hydrogen distribution in the alloy bulk. The same hydrides phases present before cycling were also observed after 20 cycles. However, transition phases poorer in hydrogen than the dominant one may precipitate at the interface with the substrate. The evolution of these transitions phases with the temperature increase will be investigated by TEM in-situ heating in the next future.

Microstructure Formation of High Pressure Torsion Processed (α + γ) Two Phase Stainless Steel

(α + γ) two phase stainless steel (Fe-21%Cr-4.8%Ni-1.5%Mo) powder was processed by high pressure torsion (HPT) and consolidation at room temperature. The received powder had fully α single phase due to the rapid cooling during gas atomizing process. Specimens after HPT process were heat treated at 1173K for 3.6ks. It was revealed that the decomposition of α phase to γ took place during the heat treatment. Detailed microstructure observation showed that an equiaxed (α + γ) micro-duplex structure was developed and its average grain size was approximately 3.2 micrometers. The same heat treatment given to the material without HPT resulted in a coarse two phase microstructure.Therefore, it is considered that an ultra fine grained microstructure was caused by increasing of nucleation sites for γ phase due to severe plastic deformation (SPD) of HPT process. Electron backscatter diffraction patterns (EBSD) analysis indicated that α phase has a {110}/ND strong texture, that is, the α phase seems to have single orientated coarse grain structure. The γ precipitates indicated a {111}/ND strong texture, and the crystallographic orientation relationship of Kurdjumov-Sachs was observed.

On the forbidden and the optimum crystallographic variant of rutile in garnet

In many inclusion–host systems with similar oxygen packing schemes, the optimum crystallographic orientation relationship (COR) between the inclusion and the host is mostly determined by matching the similar oxygen sublattices of the two structures. In contrast, the prediction of the optimum COR or even just the rationalization of the observed COR(s) between an inclusion and host with incompatible oxygen sublattices, like rutile–garnet, is not straightforward. The related documentation for such cases is therefore limited. Given the abundant crystallographic data for the rutile–garnet system acquired by transmission electron microscopy and electron backscatter diffraction methods recently, this problem can now be examined in detail for the critical structural factors dictating the selection of optimum COR in such a structurally complicated system. On the basis of the unconstrained three-dimensional lattice point match and structural polyhedron match calculated for the observed CORs, it becomes clear that the prerequisite of optimum COR for rutile (rt) in garnet (grt) is to have most of their octahedra similarly oriented/inclined in space by aligning 〈103〉rt and 〈111〉grt for needle extension growth. Further rotation along the 〈103〉rt//〈111〉grt direction then leads to the energetically most favorable COR-2 variant with a good lattice point match defined by the coincidence site lattice (CSL) and a good topotaxial match of the constituent polyhedra at the CSL points, leaving unfavorable COR-1′ in the forbidden zones. This understanding sheds light not only on hierarchical energetics for the selection of inclusion variants in a complicated inclusion–host system, but also on yet-to-be-explored [UVW]-specific CORs and hetero-tilt boundaries for composite materials in general.

Preferential Nucleation during Polymorphic Transformations.

Polymorphism is the ability of a solid material to exist in more than one phase or crystal structure. Polymorphism may occur in metals, alloys, ceramics, minerals, polymers, and pharmaceutical substances. Unresolved are the conditions for preferential nucleation during polymorphic transformations in which structural relationships or special crystallographic orientation relationships (OR’s) form between the nucleus and surrounding matrix grains. We measured in-situ and simultaneously the nucleation rates of grains that have zero, one, two, three and four special OR’s with the surrounding parent grains. These experiments show a trend in which the activation energy for nucleation becomes smaller – and therefore nucleation more probable - with increasing number of special OR’s. These insights contribute to steering the processing of polymorphic materials with tailored properties, since preferential nucleation affects which crystal structure forms, the average grain size and texture of the material, and thereby - to a large extent - the final properties of the material.

Microstructure and growth of epitaxial nano-scale LaBaCo2O5.5+δ islands on (La,Sr)(Al,Ta)O3 substrate

Epitaxial nano-scale LaBaCo2O5.5+δ (LBCO) islands are prepared on (La,Sr)(Al,Ta)O3 (LSAT) substrates by pulsed laser deposition technique. The microstructure of these islands is investigated by aberration-corrected (scanning) transmission electron microscopy. These islands exhibit morphologies of truncated octahedron with {111}LBCO side surfaces and form on nano-sized {111}Co3O4 faceted Co3O4 secondary phase that grows directly on the substrate. The crystallographic orientation relationships between the LBCO film and the LSAT substrate, as well as between the LBCO film and the Co3O4 secondary phase are determined. The atomic structure of the coherent interfaces between the Co3O4 phase and the LBCO islands is revealed by the atomic-resolution high-angle annular dark field images. Based on the obtained structural results, the growth mechanism of the islands is proposed and discussed.

Crystallographic Orientation Relationships of Grain Boundary Alpha in Additively Manufactured Ti-6Al-4V

Crystallographic Orientation Relationships of Grain Boundary Alpha in Additively Manufactured Ti-6Al-4V

Temporal evolution of coherent precipitates in an aluminum alloy W319: A correlative anisotropic small angle X-ray scattering, transmission electron microscopy and atom-probe tomography study

Small-angle X-ray scattering (SAXS), transmission electron-microscopy (TEM), and atom-probe tomography (APT) are utilized correlatively to study the evolution of nanometer length-scale coherent precipitates in a commercial age-hardenable aluminum alloy, W319. SAXS, with its high-field-of-view and resultant large statistics, perfectly complements TEM and APT at the nanometer length-scale. The combined results provide a comprehensive description of the evolution of the fine precipitates. W319 exhibits two types of fine coherent precipitates on aging namely, θ′ and Q, whose temporal evolution has been studied using time-resolved in situ SAXS analyses at three different aging temperatures: 438, 463, and 533 K. Complementary information about the morphology, dimensions and number density of the precipitates were determined from ex situ APT and TEM analyses. Coherent precipitates from a single grain of the α-Al-matrix of W319 give rise to an anisotropic SAXS signal, which is subsequently simulated, taking into account the relative orientation of the sample and the crystallographic orientation relationships of the different precipitates. The simulated anisotropic SAXS intensity, based on the results from APT and TEM, is validated utilizing the experimentally obtained 2D SAXS patterns. This permits us to determine the dimensions and number densities of the precipitates from anisotropic SAXS signals, and a complete quantitative analysis of the in situ temporal evolution of the coherent precipitates is performed. Additionally, the present study demonstrates an alternative technique for extracting structural parameters from anisotropic SAXS analyses. The methodology presented herein will be useful for age-hardening analyses of commercial age-hardenable Al-based alloys and Ni-based super alloys.

Investigation of the crystallographic orientations of the β-Mg17Al12 precipitates in an Mg-Al-Zn-Sn alloy

The crystallographic orientation relationships between β-Mg17Al12 precipitates and α-Mg matrix were investigated in the Mg-Al-Zn-Sn alloy. New orientation relationships were observed and the growth direction of the particles with new orientation relationships was along the [0002]α direction of the magnesium matrix. One of the orientation relationships was analyzed and identified as 12̅10α//111̅β,0001α//12̅1̅β. The stereographic projection of the newly observed orientation relationship was calculated and discussed. Moreover, the interfaces between the β-Mg17Al12 precipitates and α-Mg matrix and two β-Mg17Al12 particles were studied.

Microstructural characterization and mechanical properties of TiC/near-α Ti composite obtained at slow cooling rate

In this paper, microstructural characterization and mechanical properties of 10vol% TiC/Ti-6Al-3Sn-3.5Zr-0.4Mo-0.75Nb-0.35Si composite obtained at slow cooling rate has been discussed. Equiaxed or near-equiaxed α phase was formed in the composite when cooled from above the β-transus temperature at a cooling rate of 10°C/min. This is due to the fact that α precipitates can heterogeneously nucleate on TiC particles during the slow-cooling process. It was obtained that the lattice disregistry between TiC and α precipitates was only 3.8%, which corresponds to the crystallographic orientation relationship of [2-1-10]α//[011]TiC; (0001)α//(1-11)TiC. The tensile results showed that heat treatment improved UTS and elongation, simultaneously, below 700°C. The enhancement of UTS is mainly attributed to solid solution strengthening of C in matrix since about 5.5vol% TiC dissolved into matrix after heat treatment. The obvious increase in room-temperature elongation is because of the formation of equiaxed microstructure and the reduction in the sizes of spheroidised TiC particles. With the increase of temperature, the discrepancy in UTSs of the as-cast and heat-treated composites became small.

Observation of Sb2S3-type post-post-perovskite in NaFeF3. Implications for ABX3 and A2X3 systems at ultrahigh pressure

AbstractWe describe the structures and transformations that lead to the crystallization of a post-post-perovskite of Sb2S3 type in a GdFeO3-type fluoroperovskite system at high-pressure conditions, through use of large-volume powder and single-crystal x-ray diffraction techniques. The results of this analysis gives unique access to the relative crystallographic orientations of all the polymorphs encountered (GdFeO3 type, CaIrO3 type and Sb2S3 type). We use this information to extend this description to include other calculated and observed forms that are competitive in ABX3 and A2X3 stoichiometries (e.g. α-Gd2S3 and Be3N2 types) and provide substantial information on inter-relationships between these structures. Such information is critical to the interpretation of transition mechanisms, predicting transition sequences and to the expression of directional properties in those transformed structures. The transformation from CaIrO3 type to Sb2S3 type is group-subgroup, from Cmcm with fc2a, to Pnma c5, with no observable volume change, but considerable change to the morphology of the lattice. There is a concomitant increase in coordination and average bond length compared to the post-perovskite form of NaFeF3.

Phase evolution and crystallography of precipitates during decomposition of new “tungsten-free” Co(Ni)–Mo–Al–Nb γ–γ′ superalloys at elevated temperatures

This article reports the microstructural stability and consequent phase decomposition including the appearance of topologically close-packed (TCP) phases at high temperature of recently discovered tungsten-free gamma-gamma' alloys of base composition Co-10Al-5Mo-2Nb with or without the addition of Ni and Ti. On prolonged aging at 800 degrees C of the Co-10Al-5Mo-2Nb alloy, needle-shaped DO19-ordered precipitates with stoichiometry of Co-3(Mo, Nb) start appearing in the microstructure. In addition, growth of cellular domains from the grain boundaries featuring a three-phase composite lamellar structure could be observed. These phases are fcc gamma-Co with composition different from the original matrix, CoAl with B2 ordering and Co-3(Mo, Nb) with DO19 ordering. All the phases exhibit well-defined crystallographic orientation relationships. The decomposition of the alloys depends on the solvus temperature of the gamma' phase. The Ni-containing alloy exhibits no phase decomposition until 100 h of aging at 800 degrees C without any significant effect on gamma' volume fraction (76 %). However, at 950 degrees C, the alloy decomposes leading to the appearance of four different phases including TCP phases: a Cr3Si-type cubic phase, a hexagonal Laves phase, rhombohedral mu phase, and solid solution of Co phase. The gamma-gamma' microstructure in the Co-10Al-5Mo-2Nb and Co-30Ni-10Al-5Mo-2Ta alloys is not stable at 800 and 950 degrees C, respectively, on long-term aging. This shows that the measured solvus temperatures (i.e., 866 and 990 degrees C) are metastable solvus temperatures. We also report that the Ti-containing alloy exhibits superior stability with no evidence of either TCP phase formation or any other decomposition of gamma' precipitates, even after aging at 950 degrees C for 100 h.

Fusion zone microstructure evolution of fiber laser welded press-hardened steels

Fusion zone microstructures of fiber laser welded Al-Si coated press-hardened steels at pre- and post-press-hardened conditions were analyzed using transmission electron microscopy (TEM). TEM and nanoindentation studies suggest that dislocation-free δ-ferrite phase formed in the weld metal (by ingress of the Al-Si surface coating into the fusion zone) exhibits lower nanohardness compared to α-ferrite transformed after press hardening. The nanoscale properties of δ-ferrite, α-ferrite, and martensite and their crystallographic orientation relationships are reported.