Electron Beam Floating Zone Melting Research Articles

Preparation, Deformation Behavior and Irradiation Damage of Refractory Metal Single Crystals for Nuclear Applications: A Review.

Refractory metal single crystals have been applied in key high-temperature structural components of advanced nuclear reactor power systems, due to their excellent high-temperature properties and outstanding compatibility with nuclear fuels. Although electron beam floating zone melting and plasma arc melting techniques can prepare large-size oriented refractory metals and their alloy single crystals, both have difficulty producing perfect defect-free single crystals because of the high-temperature gradient. The mechanical properties of refractory metal single crystals under different loads all exhibit strong temperature and crystal orientation dependence. Slip and twinning are the two basic deformation mechanisms of refractory metal single crystals, in which low temperatures or high strain rates are more likely to induce twinning. Recrystallization is always induced by the combined action of deformation and annealing, exhibiting a strong crystal orientation dependence. The irradiation hardening and neutron embrittlement appear after exposure to irradiation damage and degrade the material properties, attributed to vacancies, dislocation loops, precipitates, and other irradiation defects, hindering dislocation motion. This paper reviews the research progress of refractory metal single crystals from three aspects, preparation technology, deformation behavior, and irradiation damage, and highlights key directions for future research. Finally, future research directions are prospected to provide a reference for the design and development of refractory metal single crystals for nuclear applications.

Compressive Property and Toughening Mechanism of Directionally Solidified Fe(Al, Ta)/Fe2Ta (Al) Eutectic Composites

Herein, Fe(Al, Ta)/Fe2Ta(Al) eutectic composites are prepared using the electron beam floating zone melting directional solidification technique. The compression and fracture toughness properties of Fe(Al, Ta)/Fe2Ta(Al) eutectic composites at different solidification rates are studied with compression and three‐point bending experiments. The toughening mechanism of the material is also analyzed from morphology, composition, and microstructure. The results show that the yield strength and compression properties of the Fe(Al, Ta)/Fe2Ta(Al) eutectic composite are increased with the increase of the solidification rate. The room‐temperature fracture toughness reaches 30.5 MPa m1/2 when the solidification rate is 4 mm min−1. In addition, the material exhibits high strength performance at room temperature. However, it exhibits poor strength and excellent plasticity due to the softening effect of recrystallization at 600 °C. The toughening mechanism of the Fe(Al, Ta)/Fe2Ta(Al) eutectic composites can be summarized as crack blunting, crack branching, crack deflection, and local deformation.

A direct evidence for lattice selective rotation of molybdenum alloys single crystals in tensile deformation

The Mo-Nb-W-Zr quaternary single crystals were prepared using the electron beam floating zone melting technique. Samples fractured under tension were sectioned along the axial direction. The results revealed an absence of the single crystal-to-polycrystal transition during the tensile process. However, there was a noticeable alteration in crystal orientation between regions near and far from the fracture site. Upon analyzing three distinct regions, it was observed that the axial crystal plane index gradually shifted from the original (-1–11) towards the direction of (-110), passing through (-2–21), (-3–31), and (-4–41). The fracture occurred precisely when the crystal plane twisted to this (-110) direction. This implies that {110} represents a lattice-selective rotation for molybdenum-based single crystal torsion when subjected to stretching along the <111> direction.

Preparation of Macrocrystalline Tungsten-Based Alloys by Electron-Beam Floating Zone Melting

Preparation of Macrocrystalline Tungsten-Based Alloys by Electron-Beam Floating Zone Melting

Directional solidification of Fe-Al-Ta eutectic by electron beam floating zone melting

Fe-Al-Ta eutectic composites have been paid more attentions for high temperature application. Nevertheless, still there is a lack of research on microstructural characteristics and crystal growth mechanism of this eutectic obtained by high temperature gradient directional solidification technique. As such, Fe-Al-Ta eutectic composites were prepared by high temperature gradient electron beam floating zone melting technique in the present paper. Microstructures, solid/liquid interface morphologies and preferential orientations of the Fe-Al-Ta eutectic composites at different solidification rates were studied. Moreover, effect of interface perturbation wavelength on stability of the solid/liquid interface was calculated according to M-S theory and Kurz-Fisher model, respectively. These are consistent with the experimental results well.

Single-crystal growth of iridium with [100] and [110] orientations by electron beam zone melting

Single crystal of iridium with two different orientations, [100] and [110] has been successfully prepared by electron-beam floating zone melting (EBFZM). The experimental results showed that the iridium single crystal with [100] orientation could be directly prepared without seeding at a low growth rate below 3 mm/min, and the single crystal with [110] orientation could be only obtained by seeding. The competitive growth of the bicrystal demonstrated that the [100] orientation of the iridium single crystal can overwhelm that of the [110] orientation at a growth rate of 2 mm/min. Moreover, the interface growth undercooling including curvature undercooling and kinetic undercooling has been calculated for iridium single crystal with these two orientations. The calculated data and analysis agree well with the experimental results.

Numerical and experimental study of electron beam floating zone melting of Iridium single crystal

Both numerical and experimental approaches were conducted to investigate the electron beam floating zone melting (EBFZM) of iridium crystal. A finite element model was established and the temperature fields under different processing parameters were calculated and discussed. The heating power, the rod diameter and the movement of heating source significantly influence the temperature distribution in the iridium rod. Once the heating starts, the temperature quickly increases and gradually reaches the steady state. The melting zone enlarges with the increase of heating power, and the critical power for obtaining a complete melting zone is 5.5kW∼6.0kW in 20mm-diameter Iridium rod. With the upward movement of heating source, the melting zone obviously enlarges and the lower solid/liquid (S/L) interface becomes more planar. Then how to get a complete melting zone with a suitable volume and the control of a planar S/L interface were discussed. An optimized processing window was proposed and applied to the EBFZM of iridium crystal. An iridium rod 20mm in diameter was successfully produced and the microstructural morphologies indicated that the initial polycrystalline microstructure will evolve into single crystal.

Study of macro- and micro-segregation of iridium in molybdenum single crystals after electron beam zone melting

AbstractThe aim of the work was to study the creation of micro- and macro-segregation of iridium in low-alloyed molybdenum single crystals after electron beam zone melting (floating zone technique) depending on various conditions of crystallization. In order to evaluate relations between the chemical inhomogeneity and structural defects and their influence on properties of single crystals, the dependence of concentration and character of distribution of admixtures under various crystallization conditions on the origin of concentration undercooling and dislocation substructure of molybdenum single crystals prepared by electron beam floating zone melting was experimentally investigated.

Directional solidification of Ni–Ni3Si eutectic in situ composites by electron beam floating zone melting

Combining the intermetallic compound with the ductile metal at the eutectic composition is one promising method to improve the ductility of the intermetallic compound. This paper reports the microstructure and the micro-hardness of the Ni–Ni3Si eutectic in situ composites prepared by electron beam floating zone melting technique. Ni–Ni3Si eutectic in situ composites display regular lamellar eutectic structure at the solidification rate R=0.3–4.0mm/min. The lamellar spacing is decreased with the increase of the solidification rate. The phase composition of the Ni–Ni3Si eutectic in situ composites is also determined by X-ray diffraction. Ni–Ni3Si eutectic in situ composites present lower micro-hardness than pure Ni3Si, although a small quantity of metastable Ni31Si12 phase is formed during the directional solidification process.

Preparation and microstructure evolution of directionally solidified Al2O3/YAG/YSZ ternary eutectic ceramics by a modified electron beam floating zone melting

We report the first growth of Al2O3/YAG/YSZ ternary eutectic in-situ composite ceramics by a modified electron beam floating zone melting technique with high temperature gradient. At optimized solidification conditions, high density (>99.5%) Al2O3/YAG/YSZ bulk eutectic ceramic rods with diameter of 2–4mm and length up to 50mm are successfully obtained. The grown composite ceramics present highly aligned irregular eutectic lamellae parallel to growth direction in stable growth zone at low rates, consisting of homogeneously distributed Al2O3, YAG and YSZ phases in the submicron size. The coarse primary Al2O3 or YAG phases with strong faceted characteristic are preferred to form in the initial growth zone. The phase size and mean interphase spacing λ rapidly decrease with increasing solidification rate V where the relationship λ2V=constant is obeyed at V<90mm/h. The cellular eutectic structures with regular lamellae in the intra-cellular region are produced at high growth rate.

Microstructure, growth mechanism and mechanical property of Al 2O 3-based eutectic ceramic in situ composites

Directionally solidified Al 2O 3-based eutectic ceramic in situ composites with inherently high melting point, low density, excellent microstructure stability, outstanding resistance to creep, corrosion and oxidation at elevated temperature, have attracted significant interest as promising candidate for high-temperature application. This paper reviews the recent research progress on Al 2O 3-based eutectic ceramic in situ composites in State Key Laboratory of Solidification Processing. Al 2O 3/YAG binary eutectic and Al 2O 3/YAG/ZrO 2 ternary eutectic ceramics are prepared by laser zone melting, electron beam floating zone melting and laser direct forming, respectively. The processing control, solidification characteristic, microstructure evolution, eutectic growth mechanism, phase interface structure, mechanical property and toughening mechanism are investigated. The high thermal gradient and cooling rate during solidification lead to the refined microstructure with minimum eutectic spacing of 100 nm. Besides the typical faceted/faceted eutectic growth manner, the faceted to non-faceted growth transition is found. The room-temperature hardness H V and fracture toughness K IC are measured with micro-indentation method. For Al 2O 3/YAG/ZrO 2, K IC = 8.0 ± 2.0 MPa m 1/2 while for Al 2O 3/YAG, K IC = 3.6 ± 0.4 MPa m 1/2. It is expectable that directionally solidified Al 2O 3-based eutectic ceramics are approaching practical application with the advancement of processing theory, technique and apparatus.

A modified preparation technique and characterization of directionally solidified Al 2O 3/Y 3Al 5O 12 eutectic in situ composites

Generally, the electron beam floating zone melting (EBFZM) technique can only be used for preparing conductive materials but is not available for nonconductive ones. In this paper, a modified EBFZM technique has been developed to prepare directionally solidified Al2O3/Y3Al5O12 eutectic in situ composites (nonconductive materials). The eutectic obtained shows ultra-fine interphase spacing with complex network structure and the irregular growth mechanism is investigated. Additionally, two new microstructures with regular growth morphology are observed and their formations are discussed.

Effect of the Ge content on the Schottky barrier height in structures based on Si1 − x Ge x solid solution

The subject of investigation is the influence of the Ge content on the Schottky barrier height in Au-p-i-n/Al structures based on Si1 − xGex (0 < x < 0.26) solid solutions grown by electron-beam floating-zone melting. In Au-i-Si1 − xGex, Au-αGe/Si(Li), Au-αGe/Si, and Au-n-Si1 − xGex structures, the height of the barrier is about 1 eV, which exceeds the average value of this parameter for silicon available in the literature. It is shown that an excess Ge concentration in the near-surface region of the Si1 − xGex crystal causes self-passivation of the surface, which leads to a rise in the barrier height. In the Au-i-Si1 − xGex structures, the Schottky barrier height increases from 0.97 to 1.03 eV as Ge content x increases from 0 to 0.11.

Microstructure and field emission properties of the Si–TaSi 2 eutectic in situ composites by electron beam floating zone melting technique

The directionally solidified Si–TaSi 2 eutectic in situ composites, which have highly aligned and uniformly distributed TaSi 2 fibers embedded in the Si continuous matrix, are obtained by electron beam floating zone melting (EBFZM) technique at the solidification rate range 0.3–9.0 mm/min. The preferential orientation of the Si–TaSi 2 eutectic is also studied by selected area electron diffraction (SAED), which is [0 1¯ 1¯]Si∥[0 0 0 1]TaSi 2 and (0 1¯ 1)Si∥(0 1¯ 1 1)TaSi 2. Moreover, field emission properties of the Si–TaSi 2 eutectic in situ composites are investigated by transparent anode imaging technology. Approximately straight F–N curves show that this material has excellent field emission properties.

The preferential orientation of the directionally solidified Si–TaSi 2 eutectic in situ composite

The Si–TaSi 2 eutectic in situ composite is a favorable field emission material due to relatively low work function, good electron conductivity, and three-dimensional array of Schottky junctions grown in the composite spontaneously. The preferential orientation during directional solidification is determined by the growth anisotropy. In order to obtain the preferential direction of the steady-state crystal growth, the transmission electron microscopy (TEM) is used for analysis. It is found that the preferential orientation of the Si-TaSi 2 eutectic in situ composite prepared by Czochralski (CZ) technique is [3 3¯ 2¯] Si∥[0 0 0 1] TaSi 2, (2 2 0)Si∥(2 2¯ 0 0) TaSi 2. Whereas the preferential orientation of the Si–TaSi 2 eutectic in situ composite prepared by electron beam floating zone melting (EBFZM) technique is [0 1¯ 1¯ ]] Si∥[0 0 0 1] TaSi 2,(0 1¯ 1) Si∥(0 1¯ 1 1)TaSi 2. The preferential directions of the Si-TaSi 2 eutectic in situ composites prepared by two kinds of crystal growth techniques are distinctly different from each other, which results from different solid–liquid interface temperatures on account of the different crystal growth conditions, e.g. different solidification rate, different temperature gradient, different solid–liquid interface curvature and different kinetic undercooling.

Microstructure and properties of Si-TaSi2 eutectic in situ composite for field emission

The Si-TaSi2 eutectic in situ composite for field emission is prepared by electron beam floating zone melting (EBFZM) technique on the basis of Czochralski (CZ) crystal growth technique. The directional solidification microstructure and the field emission properties of the Si-TaSi2 eutectic in situ composite prepared by two kinds of crystal growth techniques have been systematically tested and compared. Researches demonstrated that the solidification microstructure of EBFZM can be fined obviously because of the relatively high solidification rate and very high temperature gradient, i.e. both the diameter and inter-rod spacing of the TaSi2 fibers prepared by EBFZM technique were decreased, and the density and the volume fraction of the TaSi2 fibers prepared by EBFZM technique were increased in comparison with that of the TaSi2 fibers prepared by CZ method. Therefore the field emission property of the Si-TaSi2 eutectic in situ composite prepared by EBFZM can be improved greatly, which exhibits better field emission uniformity and straighter F-N curve.

Microstructure and Mechanical Properties of an Advanced Niobium Based Ultrahigh Temperature Alloy

The microstructure and mechanical properties including room temperature fracture toughness Kq, tensile strengthσb and elongationδ at 1250°C of the Nb based alloy directionally solidified in an electron beam floating zone melting (EBFZM) furnace have been evaluated. The microstructure is primarily composed of Nb solid solution (Nbss), α-(Nb)5Si3 and (Nb)3Si phases. After directional solidification with the moving rate of electron beam gun R being respectively 2.4, 4.8 and 7.2 mm/min, the primary Nbss dendrites, Nbss + (Nb)5Si3/(Nb)3Si eutectic colonies (lamellar or rod-like) and divorced Nb silicide plates align along the longitudinal axes of the specimens. When R = 2.4 mm/min, the best directional microstructure is obtained. Directional solidification has significantly improved theσb at 1250°C and Kq. The maximumσb occurs for the specimens with R = 2.4 mm/min and is about 85.0 MPa, meanwhile, the Kq is about 19.4 MPam1/2.

Microstructure characteristics and interface morphology evolvement of Si-TaSi 2 eutectic in situ composite for field emission

As one of the semiconductor-metal eutectic (SME) composites, Si-TaSi 2 eutectic composite has many characters such as the high melting point of TaSi 2 material, the large density of TaSi 2 fibers incorporated into the Si matrix, three-dimensional array of Schottky junctions grown in the composite spontaneously. So it is an ideal candidate for field emission array cathodes. In this paper, the directionally solidified Si-TaSi 2 eutectic in situ composite for field emission is prepared by means of the electron beam floating zone melting (EBFZM) technique on the basis of Czochralski (CZ) method. The Si-TaSi 2 eutectic in situ composite, which has high-aligned and uniformly distributed TaSi 2 fibers in the Si matrix, can be obtained when the solidification rate changes from 0.3 to 9.0 mm/min. As the solidification rate is increased, both the fibers’ diameter and inter-rod spacing are decreased, while the fibers’ density and the volume fraction are increased. Moreover, the transition from a planar interface to cellular interface and then to planar interface morphologies with increasing velocity is observed with the zero power method.

Preparation and Thermoelectric Properties of Polycrystalline Si0.4Ge0.6

Polycrystalline Si0.4Ge0.6 was prepared by electron-beam float-zone melting, and its thermoelectric properties were studied in the intrinsic region. The samples were found to be p-type, with a room-temperature resistivity from 5 to 20 Ωcm. The thermoelectric figure of merit of the alloy in the intrinsic region (500–1000 K) is lower than that of heavily doped alloys. Above 1000 K, a sharp rise in its thermoelectric figure of merit would be expected.

Unidirectional Solidification of a Nb&lt;sub&gt;ss&lt;/sub&gt;/Nb&lt;sub&gt;5&lt;/sub&gt;Si&lt;sub&gt;3&lt;/sub&gt; In-Situ Composite

The directionally solidified specimens of Nb-13.52 Si-22.60 Ti–6.88 Hf–2.54 Cr–2.24 Al alloy were prepared in an electron beam floating zone melting furnace at the withdrawing rate of 0.1, 0.3, 0.6, 1.0, 2.4 and 6.0 mm/min. All the primary Nb solid solution (Nbss) columns, Nbss + (Nb)3Si/(Nb)5Si3 eutectic colonies and divorced (Nb)3Si/(Nb)5Si3 plates or chains align well along the longitudinal axis of the specimens. With increasing of the withdrawing rate, the microstructure is gradually refined, and the amount of Nbss + (Nb)3Si/(Nb)5Si3 eutectic colonies increases. Both the room temperature ultimate tensile strength σb and fracture toughness KQ are improved for the directionally solidified specimens. The tensile fracture occurs in a cleavage way.