Phase Growth Mechanism Research Articles

Growth and phase transition properties of Ta-doped VO2 single crystal microtubes

Ta-doped VO2 single crystal microtubes with rectangular cross-sections were grown by a thermal oxidation process from V–Ta alloy foils in air. Characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy revealed their morphology as hollow, rod-like single crystals. Phase transition examinations used differential scanning calorimetry demonstrated that Ta doping can effectively decrease the metal-insulator transition temperatures of VO2 by approximately 9.8 °C/at. % Ta. The phase transition behavior and growth mechanism of Ta-doped VO2 single crystal microtubes are also elucidated.

Diffusion-controlled growth mechanism of phases and the microstructural evolution in the Ni-Zn system

The diffusion-controlled growth mechanism of the phases and microstructural evolution in correlation to estimated diffusion coefficients are described in solid Ni-solid Zn and solid Ni-liquid Zn diffusion couples that mimic the hot-dip galvanization of Ni pre-coated steel. Contrary to earlier belief, the location of the Kirkendall marker plane is detected not at the δ-NiZn8/Zn interface but inside the δ-NiZn8 phase indicating the role of both the diffusing elements Ni and Zn on the evolution of duplex morphology in this phase. Further, the growth of γ1-NiZn3, and γ-Ni2Zn11 phase layers with distinct microstructures are identified contrary to the belief that there is only one intermediate phase γ-Ni2Zn11 over this composition range. This study explains the role of relative mobilities of the elements behind the characteristic microstructural evolution in this system of technological importance.

Atom-scale characterization and 2D/3D modeling of carbides and Fe Co phases in Stellite 6 laser clad coating after aging treatment

This study applied various aging treatment (AT) times at 650 °C in Stellite 6 laser cladding layer, conducted the atom-scale characterization of stacking faults (SFs) and nanoscale M23C6 carbides, described the martensitic transformation of γ → ε, and discussed on the growth mechanism of FeCo and M23C6 phases by 3D/2D modeling. Results show the formation of three distinct regions relative to Fe diffusion, namely, interfacial layer with FeCo and M23C6 phases, Fe diffusion-affected zone with FexCoy distribution at the edge of M23C6 carbides along grain boundary, and Fe diffusion-unaffected zone with abundant carbide precipitation and SF generation. In addition, the formation of M23C6 and FeCo phases conformed to dynamics and thermodynamics. Suzuki effect influence the nanoscale carbides with profile and growing direction of [121¯] and [110], respectively, and martensite transformation occurred on (1¯11¯)γ parallel to (0002)ε as characterized by 2D modeling and HRTEM. The microhardness of surfacing layer was measured in diverse zones, and the results present that AT softened the interfacial layers but increased the hardness of Fe diffusion-affected zones and Fe diffusion-unaffected zones.

Facile and Efficient Preparation of High-Purity Black Phosphorus Based on a Vapor–Solid–Vapor Phase Growth Mechanism

Facile and Efficient Preparation of High-Purity Black Phosphorus Based on a Vapor–Solid–Vapor Phase Growth Mechanism

3D morphological evolution and growth mechanism of proeutectic FeAl3 phases formed at Al/Fe interface under different cooling rates

• The morphologies of proeutectic FeAl 3 ranging from faceted polygonal prism to non-faceted rods with radial branches can be controlled by increasing the cooling rate. • The crystallographic growth directions, facets and branching behaviors of diverse proeutectic FeAl 3 morphologies were quantitated effectively based on the reconstructed 3D structures. • At a higher cooling rate, twinning mechanism plays a leading role in the formation and growth of FeAl 3 . The 3D morphologies and growth mechanisms of proeutectic FeAl 3 at the Al/Fe interface under different cooling rates were studied by synchrotron X-ray tomography. With increasing cooling rate, FeAl 3 crystals developed from faceted polygonal prism, plates with flat surface, thin ribbon-like with periodic undulating surface to non-faceted rods with radial dendrites in cross section, indicating a gradual interface growth mode transition from two-dimensional layer growth to continuous growth. At a higher cooling rate, twinning mechanism plays a leading role in the formation and growth of FeAl 3 . A link between the morphologies, twinning and crystallographic structure was established based on quantitative analyses on the 3D structures.

Ln2Te6O15 (Ln = La, Gd, and Eu) "Anti-Glass" Phase-Assisted Lanthanum-Tellurite Transparent Glass-Ceramics: Eu3+ Emission and Local Site Symmetry Analysis.

The presence of lanthanide-tellurite "anti-glass" nanocrystalline phases not only affects the transparency in glass-ceramics (GCs) but also influences the emission of a dopant ion. Therefore, a methodical understanding of the crystal growth mechanism and local site symmetry of doped luminescent ions when embedded into the precipitated "anti-glass" phase is crucial, which unfolds the practical applications of GCs. Here, we examined the Ln2Te6O15 "anti-glass" nanocrystalline phase growth mechanism and local site symmetry of Eu3+ ions in transparent GCs produced from 80TeO2-10TiO2-(5 - x)La2O3-5Gd2O3-xEu2O3 glasses, where x = 0, 1, 2. A crystallization kinetics study identifies a unique crystal growth mechanism via a constrained nucleation rate. The extent of "anti-glass" phase precipitation and its growth in GCs with respect to heat-treatment duration is demonstrated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis. Qualitative analysis of XRD confirms the precipitation of both La2Te6O15 and Gd2Te6O15 nanocrystalline phases. Rietveld refinement of powder X-ray diffraction patterns reveals that Eu3+ ions occupy "Gd" sites in Gd2Te6O15 over "La" sites in La2Te6O15. Raman spectroscopy reveals the conversion of TeO3 units to TeO4 units with Eu2O3 addition. This confirms the polymerizing role of Eu2O3 and consequently high crystallization tenacity with increasing Eu2O3 concentration. The measured Eu3+ ion photoluminescence spectra revealed its local site symmetry. Moreover, the present GCs showed adequate thermal cycling stability (∼50% at 423 K) with the highest activation energy of around 0.3 eV and further suggested that the present transparent GCs would be a potential candidate for the fabrication of red-light-emitting diodes (LEDs) or red component phosphor in W-LEDs.

Research on Microstructure and Growth Mechanism of Different Primary Silicon in Hypereutectic Aluminum Alloy

The as-cast microstructure of a typical hypereutectic Al-25Si alloy was studied, and the growth mechanism of different primary silicon phases was analyzed. The results show that the as-cast microstructure phase composition of the alloy is mainly primary silicon and eutectic silicon. Primary silicon is mainly petal-like, massive and other complex polyhedrons, and there are a lot of cavities, cracks and other defects in the interior and boundary; Eutectic silicon is coarse and long needle-like, and the distribution is relatively messy, which seriously deteriorates the mechanical properties and cutting performance, and hinders the further application of the alloy in the field of lightweight pistons. Petal-shaped primary silicon is grown by combining five tetrahedral crystal nuclei in the melt into a decahedron, while bulk primary silicon is mainly caused by the unbalanced aggregation of impurity elements. And these two types of silicon phase growth methods are related to the twin groove growth mechanism, which is the result of a combination of multiple mechanisms.

Influence of dual Ge/C pre-amorphization implantation on the Ni1−xPtxSi phase nucleation and growth mechanisms

The impact of dual Ge/C pre-amorphization implantation (PAI) processes on the Ni0.9Pt0.1(7 nm)/Si system phase sequence has been investigated by advanced X-ray diffraction techniques and transmission electron microscopy (TEM). Using a high carbon implantation dose, it is found that the expected development of Ni-rich phases is not observed: a thick amorphous Ni1−xPtxSi layer developed until Ni0.9Pt0.1 full consumption, followed by the development of a thin crystalline Ni1−xPtxSi layer along the TiN interface. By increasing the temperature further, this last one abruptly thicken, creating the final silicide layer. An alternative model to grain boundary diffusion is discussed, accounting for the final distribution of the foreign species within the silicide layer. The use of Ge in dual Ge/C PAI processes is proposed to impact the growing mechanisms by alloying to fine-tune the carbon distribution in the substrate sub-surface.

Revealing the Nucleation and Growth Mechanisms of Fe-Rich Phases in Al-Cu-Fe(-Si) Alloys Under the Influence of Al-Ti-B

Al-5Ti-1B is commonly added to the Al alloys for grain refinement, which also affects the type, size, morphology, and formation sequence of Fe-rich intermetallic phases. The underlying nucleation and growth mechanism of Fe-rich phases under the influence of Al-5Ti-1B during the solidification of Al-Cu-Fe(-Si) alloys were systematically studied by thermodynamic calculation, and with scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), focused ion beam (FIB) coupled with transmission electron microscopy (TEM), and in-situ synchrotron X-ray radiography. The SEM and in-situ synchrotron X-ray radiography experiments revealed that the Al-5Ti-1B addition significantly reduced the size and number of primary Al3(CuFe) phases. and refined the size of α-Fe in Al-Cu-Fe-Si alloy without changing their type. This was caused by Ti solute atoms in Al melts, which limiting the nucleation and growth of primary Al3(CuFe) phases during solidification. The FIB and TEM results showed that the prior formed TiB2 particles or/and newly-formed aluminium oxide were nucleate sites for Al6(CuFe) phase and α-Fe phase in Al-Cu-Fe alloy and Al-Cu-Fe-Si alloy, respectively. The Edge-to-Edge model and orientation relationship further confirmed the experimental results. In addition, V diffusion into TiB2 particles in the Al melts to form (TiV)B2 particles and lowering the interfacial energy enhance the heterogenous nucleation for Fe-rich phases.

Nucleation and Growth of Fe-Rich Phases in Al-5Ti-1B Modified Al-Fe Alloys Using Synchrotron X-Ray Imaging and Electron Microscopy

The plate-like Fe-rich intermetallic phases directly influence the mechanical properties of recycled Al alloys, thus many attempts have been made to modify their morphology. Here, through synchrotron X-ray imaging and electron microscopy, we reveal the underlying nucleation and growth mechanism of Fe-rich phases during the solidification of Al-5Ti-1B inoculated Al-2Fe alloys. The experiment results shown that Al-5Ti-1B grain refiner and applied pressure both reduce the sizes and number of primary Al 3Fe phases, and promote the formation of eutectic Al6Fe phases. The tomography results shown that Al-5Ti-1B change the 3D morphology of primary Fe-rich phases from rod-like to branched plate-like and reduced their thickness and size. This is attributed to the Ti-containing solutes in the melts retard the diffusion of Fe atoms and the TiB2 provide possible nucleation sites for Al6Fe phases. The nucleation mechanism of Fe-rich phases is discussed in terms of experimental observation and E2EM model. It is suggested that the V segregated at the TiB2/Al6Fe interface and lower their mismatch and promote the transformation from Al3Fe to Al6Fe phases.

Growth mechanism of primary Ti5Si3 phases in special brasses and their effect on wear resistance

In the present work, in-situ Ti5Si3 reinforced special brasses were prepared by melt reaction method. The synthesized Ti5Si3 phase shows various morphologies in brasses with different Ti5Si3 content, and the 3D morphological evolution of primary Ti5Si3 and its growth mechanism were investigated. The Ti5Si3 crystal, which bears D88 hexagonal crystal structure, grows along <0001> direction and is revealed by {101̅0} faces during growth. With the increase of Ti5Si3 content in the brasses, the morphology of primary Ti5Si3 significantly changes from fibers to hexagonal prisms to short-rods with hollow. In addition, the influence of Ti5Si3 volume fraction and morphology on the wear behavior of special brass was also revealed. It was substantiated that the wear resistance increases with the increasing volume fraction of Ti5Si3, and the corresponding wear mechanism changes from delamination to slight adhesive wear and abrasive wear. However, the friction coefficient shows an abnormal increase when most of the Ti5Si3 containing hollows appears in the brass. That is mainly due to the fact that the Ti5Si3 is easier to break and fall off resulted by the hollow as a crack source, which makes it unable to resist the plastic deformation of the contact surface during the sliding.

Boron effect on phase transformation of σ and M23C6 in nimonic 105 superalloy

In this study, the formation and transformation of σ and M23C6 phases in Nimonic 105 superalloy at different level of boron were investigated. So alloys with two levels of boron were prepared and the microstructure were analyzed using optical and scanning electron microscopy and X-ray diffraction. It was found that the time of M23C6 formation, M23C6 transformation into σ phase and grain growth mechanism were influenced by boron addition. Boron segregated at the grain boundaries and changed the morphology of M23C6 from continuous to discontinuous one. M23C6 transformed to needle-like σ precipitates at 750 °C after 360 and 240 h heating and the σ volume fraction reached to 2.2 and 3.4 vol% after 500 h in the alloys containing 0.013 and 0.003 wt% B, respectively. Furthermore, the time-temperature- precipitation (TTP) diagrams of M23C6 phase were presented. It was observed that time and temperature formation of M23C6 precipitation shifted to higher times and temperatures as a result of boron addition.

Comparative Gas Sorption and Cryoporometry Study of Mesoporous Glass Structure: Application of the Serially Connected Pore Model.

Nitrogen sorption and melting and freezing of water in a small pore size mesoporous glass with irregular pore structure is studied. The analysis of the experimentally obtained data is performed using the recently developed serially connected pore model (SCPM). The model intrinsically incorporates structural disorder by introducing coupling between nucleation and phase growth mechanisms in geometrically disordered mesopore spaces. It is shown that, in contrast to the independent pore models prevailing in the literature, SCPM self-consistently describes not only boundary transitions, but also the entire family of the scanning transitions. The scanning behavior is shown to be very sensitive to microscopic details of the fluid phase distribution within the porous materials, hence can be used to check the validity of the thermodynamic models and to improve the structural analysis. We show excellent quantitative agreement between the structural information evaluated from the cryoporometry and gas sorption data using SCPM.

Ammonia decomposition and reaction by high-resolution mass spectrometry for group III – Nitride epitaxial growth

The decomposition of ammonia (NH3) in nitrogen (N2) ambient was studied under non-equilibrium conditions similar to those in a metal organic vapor phase epitaxy (MOVPE) reactor during the epitaxial growth of group-III nitrides. The gas phase was sampled at different positions and analyzed using a time-of-flight mass spectrometry system with a high resolution (better than 0.002 u). Our results expand earlier findings. Even at the high temperature of 1200 °C, only 26% of NH3 decomposed in a clean metal-free reactor, whereas a higher ratio of NH3 decomposition was realized in the presence of stainless steel. The activation energy in the clean reactor was calculated to be 0.965 ± 0.004 eV. These results demonstrate the capability of our setup and shed new light on the elucidation of the vapor phase growth mechanism of group III-nitrides by MOVPE.

Formation Procedure of Reaction Phases in Al Hot Dipping Process of Steel

This study investigated the nucleation and growth mechanism of reaction layers and phases of hot-dipped boron steel in pure Al at 690 °C for 0–120 s. In the case of a dipping time of 30 s, reaction nuclei of width 10–15 μm and height 10 μm were formed on the steel surface in the flow direction of the liquid Al. This reaction layer was formed as a mixture of θ (Fe4Al13) phase of several nm to 2 μm, θ and η (Fe2Al5) of several nm, a columnar η region, and a β (FeAl) region of 500 nm thickness at the steel interface. At the grain boundaries of ferrite, in contact with the η phase, κ (Fe3AlC) was formed. Using the calculated Fe-Al phase diagram, it was determined that when Fe was dissolved in liquid Al from the steel above 2.5 at% (0.6 wt%), the θ phase was formed. Although most of the θ phases continuously grew toward the liquid phase, the θ phase in contact with the steel was transformed into the η phase with minimal differences in composition due to the inter-diffusion of Al and Fe. It was therefore concluded that the η phase formed at the interface became a growth nucleus and grew in a columnar form toward the steel.

Facile partly templating growth of Bi 2 S 3 nanorods by in‐situ thermal sulphuration of BiOCl nanosheets and the photosensitive properties

Bi 2 S 3 nanorods were prepared by a facile in-situ thermal sulphuration method using BiOCl nanosheets as precursors. The products were characterised by X-ray diffraction, Raman scattering, Fourier-transform infrared spectroscopy and scanning electron microscopy. The optical properties were measured by ultraviolet-visible spectroscopy and photoluminescence techniques. The photosensitive properties were investigated by the photoelectrochemical method. The Bi 2 S 3 sample was of pure orthorhombic phase and composed of nanorods with average diameter of ~200 nm and length of ~2 μm. A plausible gas phase growth mechanism was proposed which involved the partly templating of the shape of precursors by transforming BiOCl nanosheets to Bi 2 S 3 nanorods. The photocurrent of the products under irradiation of solar simulator reached 1.0 μA/cm 2 without bias voltage which was ten times that of the dark current. The photoelectric measurements clearly demonstrate that the as-prepared Bi 2 S 3 nanorods possess excellent photosensitivity with stability and reproducibility, enabling the products suitable for the fabrication of high-performance photodetectors and other optoelectric devices.

High cubic phase purity and growth mechanism of cubic InN thin-films by Migration Enhanced Epitaxy

Metastable cubic InN is a promising semiconductor for developing optoelectronic, photovoltaic and electronic devices. The suitable application of the material requires a high crystalline quality and a high cubic phase purity. For this reason, it is important to identify the growth mechanism of both the cubic phase and the structural defects, as well as to quantify the cubic phase purity. In this work, we determine and quantify the cubic phase purity in c-InN samples grown by Migration Enhance Epitaxy (MEE) using Raman spectroscopy. We found, the LO and TO phonon modes attributed to the cubic phase of InN at 589 and 462cm-1, respectively. The hexagonal phase inclusions were also identified with the E2 mode observed at 488cm-1. The quantification of the cubic phase purity was performed employing a model that takes into account the intensities of the LO and E2 modes of the Raman spectra in a depth profile. The highest cubic phase purity obtained was 93.7% for a sample grown at 510°C. We also analyzed the growth mechanism of c-InN by transmission electron microscopy (TEM), finding the cubic phase, the characteristic planar defects and a small hexagonal inclusion (h-InN). The characteristic planar defects in the samples are the stacking faults (SF). We quantified the SF density using the cross section TEM images. The lowest density was 3.27×105cm-1 for the sample grown at 510°C. Additionally, the high cubic phase purity in the c-InN samples was identified in a phase map obtained by Precession Electron Diffraction.

Slip Degassing to Improve the Properties of Slip Cast and Reaction Bonded Si3N4

The effect of slip degassing on the microstructure and mechanical properties of slip cast and reaction bonded Si3N4 was studied. The slip was prepared by aqueous ball milling of silicon (Si) powder. Hydrogen bubbles, a result of Si oxidation during milling, were degassed from the slip using a combination of vacuum and heat. The slip was then cast into a plaster mould to obtain rectangular green bodies. The Si green samples were sintered in a nitrogen atmosphere at 1500°C to convert the Si to Si3N4. After that the nitrided samples were polished to dimensions of 3 x 4 x 30 mm. The density, porosity, flexural strength, phase content and microstructure of the sintered samples were studied. The results showed that the degassing process increased the slip density. After casting and subsequent nitridation, it was found that the average apparent density of the samples increased from 2.89 to 2.95 g/cm3, the porosity decreased from 52.9 to 49.5 %, and the flexural strength increased from 8.1 to 9.3 MPa, when the degassed slip was used. A microstructural examination showed that the pores in the samples were filled with whiskers, which most likely resulted from a vapor phase growth mechanism. The samples produced from the degassed slip tended to have fewer whiskers, due to the reduced pore size and volume. A comparison of the XRD patterns showed no phase differences between the samples. The appearance of Si2N2O, and SiC likely resulted from the reactions between O2 and C impurities with Si3N4.

Phase composition and growth mechanisms of half-metal Heusler alloy produced by Pulsed Laser Deposition: From core-shell nanoparticles to amorphous randomic clusters

We report on a systematic study of the experimental parameters to control size and morphology of half-metals Heusler nanoparticles synthesized by pulsed laser deposition (PLD) technique. Our findings suggest the existence of a threshold across which the mechanism of particle growth changes: core-shell NPs for higher values of laser energy and randomic amorphous structure for lower values of laser energy. The growth mechanisms are discussed in deep based on the high resolution transmission electron microscopy (HR-TEM) results; and a phase diagram was developed to summarize our findings.

Bifurcation of the Kirkendall marker plane and the role of Ni and other impurities on the growth of Kirkendall voids in the Cu–Sn system

The presence of bifurcation of the Kirkendall marker plane, a very special phenomenon discovered recently, is found in a technologically important Cu–Sn system. It was predicted based on estimated diffusion coefficients; however, could not be detected following the conventional inert marker experiments. As reported in this study, we could detect the locations of these planes based on the microstructural features examined in SEM and TEM. This strengthens the concept of the physico–chemical approach that relates microstructural evolution with the diffusion rates of components and imparts finer understanding of the growth mechanism of phases. The estimated diffusion coefficients at the Kirkendall marker planes indicates that the reason for the growth of the Kirkendall voids is the non–consumption of excess vacancies which are generated due to unequal diffusion rate of components. Systematic experiments using different purity of Cu in this study indicates the importance of the presence of impurities on the growth of voids, which increases drastically for ≥ 0.1 wt% impurity. The growth of voids increases drastically for electroplated Cu, commercially pure Cu and Cu(0.5 at.% Ni) indicating the adverse role of both inorganic and organic impurities. Void size and number distribution analysis indicates the nucleation of new voids along with the growth of existing voids with the increase in annealing time. The newly found location of the Kirkendall marker plane in the Cu3Sn phase indicates that voids grow on both the sides of this plane which was not considered earlier for developing theoretical models.