Floating Zone Melting Method Research Articles

Comprehensive microstructure regularization mechanism and microstructure–property stability at 1773 K of directionally solidified Al2O3/GdAlO3 eutectic ceramic composite

Melt grown Al2O3/GdAlO3(GAP) eutectic ceramic composite is considered as a promising ultra–high temperature structural material in fields as aerospace, power generation and so on. In order to tune the properties of directionally solidified Al2O3/GAP eutectic ceramic composite, its microstructure evolution is investigated over a wide range of compositions and solidification rates by laser floating zone melting method (LFZM). With the increase of solidification rate and the enrichment of Al2O3 phase, the eutectic microstructure undergoes a transformation from “Chinese script” irregular morphology to rod–like regular and complex regular morphology. The synergistic effects of composition and solidification rate on the microstructure regularization have been quantitatively characterized by the proportion of regular eutectic. High solidification rate (>200 μm/s) is beneficial to the formation of isothermal interface, partly inhibiting the anisotropic growth of Al2O3 faceted phase, which further promotes the coupling growth of the eutectic phases at the front of the interface and facilitates the microstructure regularization. The stability of eutectic spacing is verified to coincide with the Ostwald ripening relationship when the eutectic ceramic composite is thermally exposed at 1773 K for long–term (250 h). The microstructure coarsening rate is less than 0.003 μm/h, and the hardness slightly decreases about 4%, and the fracture toughness remains almost unchanged, which indicates excellent thermal stability of microstructure and property for the Al2O3/GAP eutectic ceramic composite at high temperature.

Effects of Solidification Conditions on Grain Refinement Capacity of TiC in Directionally Solidified Ti6Al4V Alloy

In this study, the effects of solidification conditions on the grain refinement capacity of heterogeneous nuclei TiC in directionally solidified Ti6Al4V alloy were investigated using experimental and numerical approaches. Ti6Al4V powder with and without TiC particles in a Ti6Al4V sheath was melted and directionally solidified at various solidification rates via the floating zone melting method. In addition, by using the phase field method, the microstructural evolution of directionally solidified Ti6Al4V was simulated by varying the temperature gradient G and solidification rate V. As the solidification rate increased, the increment of the prior β grain number by TiC addition also increased. There are two reasons for this: first, the amount of residual potent heterogeneous nuclei TiC is larger. Second, the amount of TiC particles that can nucleate becomes larger. This is because increasing the constitutional undercooling ΔTc leads to the activation of a smaller radius of heterogeneous nuclei and a higher nucleation probability from each radius. At a cooling rate R higher than that in the floating zone melting experiment (R = 3 to 1000 K/s), the maximum degree of constitutional undercooling ΔTc,Max has a peak value, which suggests that constitutional undercooling ΔTc has a smaller contribution at higher cooling rates, such as those that occur during electron beam melting (EBM), including laser powder bed fusion (LPBF).

Spin glass transition of single-crystalline TmFe2O4−δ

TmFe2O4 is one kind of multiferroic material in which equivalent amounts of Fe2+ and Fe3+ occupy a two-dimensional triangular lattice, leading to charge and spin frustrations. The spin frustration is expected to be increased as the fraction of Fe2+ (Fe3+) becomes larger than that of Fe3+ (Fe2+). We have grown single-crystalline TmFe2O4−δ with oxygen vacancies by using floating zone melting method and examined its magnetic properties. On cooling the compound, a long-range magnetic ordering develops around ∼240 K. With further cooling, a maximum of zero-field-cooled (ZFC) magnetization is observed at 186.2 K. The ac magnetic susceptibility obtained by ZFC process also manifests a maximum in its temperature dependence, and the variation of spin-freezing temperature with frequency of ac magnetic field is explainable in terms of the dynamic scaling law with the critical component of 8.68(8). This value suggests that the spin glass transition occurs at 186.2 K. The effect of external dc magnetic field on the irreversible transition temperature is coincident with the de Almeida–Thouless (AT) line. Aging-memory and rejuvenation effect is also observed below the spin-freezing temperature. These facts support the idea that TmFe2O4−δ undergoes spin glass transition below the ferrimagnetic transition temperature. In other words, TmFe2O4−δ can be regarded as a reentrance spin glass. It is thought that the oxygen vacancies bring about unequal number of Fe2+ and Fe3+ ions and thereby strengthen the magnetic frustration among the iron ions coupled with antiferromagnetic interactions, leading to the spin glass behavior.

Structure and Properties of the Directionally Crystallized B4C–NbB2–SiC Alloy

The 32B4C–30NbB2–38SiC composite (mol %) has been prepared by the floating zone melting method. The structure of the obtained composite consists of a coarse-grained binary eutectic (NbB2–SiC), a fine-grained ternary eutectic (B4C–NbB2–SiC), and large SiC dendrites. The effect of the crystallization rate on the structure and properties of the prepared composite is studied. The Vickers hardness, fracture toughness, and bending strength of the 32B4C–30NbB2–38SiC composite are 31–36 GPа, 4.0–5.1 GPа m1/2, and 203–252 GPa, respectively.

Toward understanding the anomalous Li diffusion in inorganic solid electrolytes by studying a single-crystal garnet of LLZO-Ta by pulsed-gradient spin-echo nuclear magnetic resonance spectroscopy.

Li diffusion was observed by 7Li nuclear magnetic resonance (NMR) spectroscopy in three single-crystal samples of LLZO-Ta (Li6.5La3Zr1.5Ta0.5O12) grown by the floating zone melting method as well as a crushed sample in this study. Previously, the pulsed-gradient spin-echo 7Li NMR method was applied to Li+ diffusion measurements in inorganic solid electrolyte powder samples. Anomalous Li+ diffusion behaviors were observed such as dependence of the observing time (Δ) and pulsed-field-gradient strength (g), and the diffusive-diffraction patterns in short Δ in the echo-attenuation plots. In the powder samples, it is uncertain that the Li ions diffuse in the bulk within grain, across grains, or both. To date, the origins of the anomalous Li+ diffusion have not yet been clearly understood. From models of atomic-level lithium pathways, the micrometer-space diffusion channels are assumed to be narrow with curvatures. In contrast to the powder samples, a single crystal is supposed to be uniform without grain boundaries and the Li ions in single-crystal samples can diffuse in the bulk with negligible effects from the surface. The single-crystal samples are expected to give us proper answers. We found that the 7Li echo-attenuation plots of the single-crystal samples showed anomalous phenomena in dependence on Δ and g with much reduced manners. We found that the phenomena are inherent characteristics of Li+ diffusion in inorganic solid electrolytes. From the aspects of Li+ carrier numbers, the fast divergent Li+ diffusion constants, observed at short Δ with small g, contribute importantly to the electrochemical high ionic conduction measured by impedance spectroscopy.

Effects of TiC Addition on Directionally Solidified Microstructure of Ti6Al4V

In this study, the effects of TiC particles as the heterogeneous nucleus on the microstructure of directionally solidified Ti6Al4V were investigated. Ti6Al4V powder containing 0.0, 0.3, 1.0, and 2.0 vol pct TiC particles in a Ti6Al4V sheath was melted and directionally solidified with a floating zone melting method. In this process, the temperature gradient G was approximately 12 K/mm, and the solidification rate R was 15 mm/min. The mean size of prior β grains decreased with increasing TiC addition. In samples containing TiC particles, some grains had an aspect ratio lower than 1. This indicated that TiC particles acted as the heterogeneous nucleus and generated fine and equiaxed prior β grains. Although the many TiC particles melted into molten Ti6Al4V and the excessively melted carbon from TiC particles precipitated as Ti2C, residual TiC particles acted as a heterogeneous nucleus.

The Directional Solidification, Microstructural Characterization and Deformation Behavior of β-Solidifying TiAl Alloy.

A β-solidifying Ti–43Al–2Cr–2Mn–0.2Y alloy was directionally solidified by the optical floating zone melting method. The microstructure is mainly characterized by γ/α2 lamellae with specific orientations, which exhibits straight boundaries. The β phase is randomly distributed in the lamellar microstructure, indicating that the β phase cannot be directionally solidified. The directional solidification of γ/α2 lamellae was not affected by the precipitation of the β phase. Hot compression tests show that the deformation behavior of the β-containing lamellar microstructure also exhibits the anisotropic characteristic. The deformation resistance of the lamellae is lowest when the loading axis is aligned 45° to the lamellar interface. Microstructural observation shows that the decomposition of the lamellar microstructure tends to begin around the β phase, which benefits from the promotion of a soft β phase in the deformation. Moreover, the deformation mechanism of the lamellar microstructure was also studied. The bulging of the γ phase boundaries, the decomposition of α2 lamellae and the disappearance of γ/γ interfaces were considered as the main coarsening mechanisms of the lamellar microstructure.

High-quality LaxCeyPr1-x-yB6 single crystal with excellent thermionic emission properties grown by optical floating zone melting method

The high-quality LaxCeyPr1-x-yB6 (x = 0.6–0.8, y = 0.1–0.3) single crystals have been firstly grown by optical floating zone melting method. The crystal structure, mechanical and thermionic emission properties of the as-grown single crystals were characterized by X-ray single crystal diffractometer, SEM, XRD, X-ray Laue diffraction. Subgrain-boundary-free [100] LaxCeyPr1-x-yB6 single crystal with a good crystalline integrity and homogeneous element distribution is obtained. The Lattice constant of LaxCeyPr1-x-yB6 single crystal is lower than that of the LaB6 single crystal. The lowest FWHM of 162.0 arcsec belongs to the La0.6Ce0.3Pr0.1B6 single crystal. The highest thermionic emission current density of 105.10 A/cm2 and the lowest work function of 2.562 eV indicate that La0.6Ce0.3Pr0.1B6 single crystal is a very promising thermionic cathode material.

Structural Analysis of Sr3NbFe3Si2O14 Single Crystal from the Langasite Family and Finding of Negative Thermal Expansion in the Range of 83–110 K

Iron-containing Sr3NbFe3Si2O14 single crystals from the langasite family, which are interesting for researchers due to their magnetic ordering at T N = 26 K, have been grown by the floating zone melting method. Accurate X-ray diffraction analysis is performed at 293 and 90.5 K using the data collected on a CCD diffractometer. To compensate for systematic errors, two data sets are collected at each temperature. The structure is refined based on averaged data set: sp. gr. P321, Z = 1, sin θ/λ ≤ 1.35 A–1; a = 8.2609(4) A, c = 5.1313(3) A at 293 K and a = 8.2344(6) A, c = 5.1243(6) A at 90.5 K; the agreement factors are R/wR = 1.18/1.03% and Δρmin/Δρmax =–0.57/0.25 e/A3 for 3583 independent reflections at 293 K and R/wR = 1.18/1.13% and Δρmin/Δρmax =–0.54/0.23 e/A3 for 3638 reflections at 90.5 K. Negative thermal expansion in the direction of the cell c axis is revealed in the range of 83–110 K.

Single crystals growth of hexaferrits M-type MTixCoxFe12−2xO19 (M = Ba, Sr) by floating zone and investigation of their magnetic and magnetoelectric properties

Floating zone melting method with optical heating is elaborated to grow single crystals of the substituted hexaferrites BaTixCoxFe12−2xO19 and SrxTixCoxFe12−2xO19 (0.8 ≤ x ≤ 2). The dynamics of the growth process is studied and results of the analysis of impurity phases appearing in the initial stages of the crystal growth are presented. Compositions and unit-cell parameters of crystals are determined. Electrical, magnetic and magnetoelectric properties of grown crystals are investigated at temperatures 2–365 K and magnetic fields up to 50 kOe. It is shown that the resistivity of annealed in oxygen crystals at room temperature is ∼106 Ohm·cm while at helium temperatures the crystals become good insulators. Magnetic measurements reveal conical spin structures in the crystals at some concentrations and temperatures. Magnetic field induced electric polarization of the low value (∼0.3 μC/m2) is detected at liquid helium temperatures for compositions with Ti and Co concentrations x = 0.8–0.9.

Peculiar magnetism of UAu2Si2

Single-crystalline UAu$_2$Si$_2$ has been grown by a floating-zone melting method, and its magnetic, thermal and transport properties have been investigated through measurements of magnetization, specific heat and electrical resistivity to reveal its peculiar magnetism. It is shown that UAu$_2$Si$_2$ undergoes a second-order phase transition at \tm = 19 K, which had been believed to be ferromagnetic ordering in the literature, from a paramagnetic phase to an uncompensated antiferromagnetic phase with spontaneous magnetization along the tetragonal $c$-axis (the easy magnetization direction). The magnetic entropy analysis points to the itinerant character of 5f electrons in the magnetic ordered state of UAu$_2$Si$_2$ with large enhancement of the electronic specific heat coefficient of $\gamma$ $\sim$ 150 mJ/K$^2$mol at 2 K. It also reveals the relatively isotropic crystalline electric field effect of this compound, with contrast to the other relative isostructural compounds. The observed magnetization curves strongly suggest that there is a parasitic ferromagnetic component developing below $\sim$ 50 K in high coercivity with the easy axis along the tetragonal $c$-axis. The results are discussed in the context of evolution of magnetism within the entire family of isostructural U$T_2$Si$_2$ compounds.

Diagnostics of impurity composition of high-purity monosilane by results of the analysis of a test silicon single crystal

Elements the 3 and 5 of groups of the Periodic System and carbon are the most important impurities in silicon. The estimation technique of carbon, boron and phosphorus impurity content in high-purity monosilane has been proposed. The technique involves the preparation of polycrystalline silicon by silane decomposition, growing a test single crystal by the floating zone melting method and analysis of single crystal samples by IR spectroscopy. Calculation of impurity concentration in polycrystalline silicon has been performed using results on their content in the test single crystal samples, data on impurity distribution in the liquid-solid system and sample coordinates along the ingot length. Effective impurity distribution coefficients in the solid-liquid system for specific growing conditions have been calculated using the Burton-Prim-Slichter equation. Results for the test silicon samples with natural isotopic composition and 28Si isotope enriched ones obtained from monosilane samples with different impurity contents have been reported. Results on IR spectroscopic studies of impurity composition for the test silicon single crystal are in agreement with the concentration data obtained by chromatography. The concentration of 3 and 5 group impurities in monosilane were in the range 4x10−9−2x10−6 at. %, and for carbon concentration was 2x10−6–6x10−4 at.%. The measurement uncertainty by IR spectroscopy does not exceed 15% for carbon impurity and 20% for boron and phosphorus. We show that the upper limit of carbon content in monosilane detected using this method is determined by its solubility in silicon, while the bottom limit depends on the detection accuracy of the IR spectroscopy technique and possible background contamination.

Control of microstructure and fracture toughness improvement of NbSi2/MoSi2 duplex lamellar silicides by TaC particles dispersion

The floating-zone melting method enabled the dispersion of TaC particles in a C40-(Mo0.85Nb0.15)Si2 single crystal. By annealing the C40 crystal, coarse C11b phases were formed around the TaC particles and the precipitation of the D88-(Mo,Nb,Ta)5Si3C phase was also induced, in addition to the development of a C40/C11b lamellar microstructure. Such a microstructure containing TaC particles led to a reduction in the orientation dependence of the fracture toughness of duplex silicide crystals.

Diagnostics of Impurity Composition of High–Pure Monosilane by Results of the Analysis of a Test Silicon Single Crystal

Elements III and V of groups of the Periodic System and carbon are the most important impurities in silicon. The estimation technique of carbon, boron and phosphorus impurity content in high − purity monosilane has been proposed. The technique involves the preparation of polycrystalline silicon by silane decomposition, growing a test single crystal by the floating zone melting method and analysis of single crystal samples by IR spectroscopy. Calculation of impurity concentration in polycrystalline silicon were performed using results on their content in the test single crystal samples, data on impurity distribution of in the liquid − solid system and sample coordinates along the ingot length. Effective impurity distribution coefficient in the «solid − liquid» system for specific growing conditions have been calculated using the Burton − Prim − Slichter equation. Results for the test silicon samples with natural isotopic composition and the enriched 28 Si isotope obtained from monosilane samples with different impurity contents have been reported. Results of IR spectroscopic research of impurity composition for the test silicon single crystal are in agreement with the concentration data obtained by chromatography. The concentration of III and V group impurities in monosilane were in the range 4 ⋅ 10 − 9 —2 ⋅ 10 − 6 at. %, and for carbon 2 ⋅ 10 − 6 —6 ⋅ 10 − 4 at.%. The measurement uncertainty by IR spectroscopy method for carbon impurity does not exceed 15 %, for boron and phosphorus — 20%. We show that the upper limit of carbon content in monosilane detected using this method is determined by its solubility in silicon, while the bottom limit depends on the detection accuracy of the IR spectroscopy technique and possible background contamination.

Effect of Interstitial Carbon Atoms on Phase Stability and Mechanical Properties of E21 (L12) Ni3AlC1-x Single Crystals

ABSTRACTSingle crystals of E21 (L12) Ni3AlC1-x were prepared by the unidirectional solidification using the optical floating zone melting method to determine their mechanical properties. Particularly the effects of interstitial carbon atoms on mechanical properties were evaluated by compression tests at room temperature. Operative slip system of E21 Ni3AlC is {111}<011> type which is the same as that of L12 Ni3Al. Strength of Ni3AlC single crystals increases with carbon concentration due to the solid solution effect, though the stress relief of yielding behavior is enhanced at the intermediate carbon content at around 3at%. A large gap appears in the carbon concentration dependence of critical resolved shear stress (as well as yield stress) at almost the same carbon content. This discontinuity in strengthening is attributed to the interaction between multiple solute carbon atoms and mobile dislocations.

About the role of melt movement during of the silicon single crystal growth by FZ method

In work the conditions of occurrence of convection in the melted zone during growth of silicon single crystals by the floating zone melting method was investigate. It are fix, that streams in the melted zone (thermogravitational, centrifugal, thermocapillary and electrodynamic) influenced on distribution of impurity in the melt and, hence, defined quality of end production

Improved Thermoelectric Properties of Bi-M-Co-O (M = Sr, Ca) Misfit Compounds by Laser Directional Solidification

In this work, improvement of the thermoelectric properties of bulk samples due to texture developed by a directional laser-assisted solidification process (laser floating zone melting method) is reported for cobaltite materials with compositions Bi2Sr2Co1.8Oy and Bi2Ca2Co1.7Oy. Sample composition and microstructure have been studied using x-ray diffraction and scanning electron microscopy. Thermoelectric properties have been measured between 4 K and 300 K by simultaneous determination of electrical resistivity and thermopower. All textured samples showed remarkable increase of power factor values as compared with conventional sintered ceramics.

Al substituted Ba-hexaferrite single-crystal films for millimeter-wave devices

Microwave and magnetic properties of single-crystal aluminum substituted barium hexaferrites BaAlxFe12−xO19 with Al substitution level x from 0 to 2 are reported. The single crystals were grown by the floating zone melting method. Films in the form of 100 μm thick, 1 mm wide, and 2 mm long resonators were used for ferromagnetic resonance (FMR) measurements in the frequency domain over 40–110 GHz for applied magnetic fields of 0–10 kOe. Based on these measurements, the hexaferrite parameters are determined. With increasing x from 0 to 2, the uniaxial magnetocrystalline anisotropy field increases from 17.88 to 33.68 kOe, while reasonable values of full FMR linewidth (35 Oe at 47 GHz and 140 Oe at 108 GHz) are maintained. These parameters ensure the potential for use of the ferrites in millimeter-wave devices.

Phase Stability and Thermoelectric Properties of Half-Heusler Compounds (Ti,M)NiSn (M = Zr, Hf)

AbstractAiming to improve thermoelectric properties of half-Heusler compounds MNiSn (M = Ti, Zr, Hf), phase equilibria in the (Ti,M)NiSn systems have been investigated focusing on the half-Heusler phase separation between TiNiSn and ZrNiSn, TiNiSn and HfNiSn. Solubility limit of an element M in each half-Heusler phase was determined by XRD and EPMA. Nearly single phase alloys were fabricated by the directional solidification using optical floating zone melting method to evaluate intrinsic thermoelectric properties of the alloys. Lattice thermal conductivity can be reduced in (Ti,M)NiSn alloys by phonon scattering due to the solid solution effect of M site substitution. Moreover, electrical properties can be enhanced by the Ti addition in (Ti,Zr)NiSn alloys. Among present MNiSn alloys, (Ti0.15,Zr0.85)NiSn alloy has the highest power factor of 5.3 mWm-1K-2 at around 745 K.

Magnetostriction and hysteresis of ⟨1 1 0⟩ oriented Tb0.29Dy0.48Ho0.23Fe2 single crystal

Magnetostriction behaviour and magnetostriction hysteresis of the single crystal alloy Tb0.29Dy0.48Ho0.23Fe2 are investigated experimentally and theoretically. The oriented ⟨1 1 0⟩ single crystals of the magnetostrictive alloy Tb0.29Dy0.48Ho0.23Fe2 are successfully prepared by the optical floating zone melting method. The single crystals are characterized by optical metallography, x-ray diffraction and x-ray Laue back-reflection measurement. The giant magnetostrictive properties are achieved in a wide operating temperature range from −60 to 80 °C. The calculated magnetostriction of the present alloy is reduced by only 6%, but the magnetostriction hysteresis (Wh) is reduced by more than 30%, compared with the traditional Terfenol-D giant magnetostrictive alloy. The magnetostriction behaviour is modelled using phenomenological theory. The rotation paths of magnetic domain moments are mathematically calculated and hence the resultant magnetostriction is obtained. The theoretical model of magnetostriction hysteresis Wh is proposed and the intrinsic factors of Wh are determined, which can well explain the pre-stress and temperature dependence of magnetostriction hysteresis.