Arc Melting Technique Research Articles

Microstructure and mechanical properties of novel ZrB2-reinforced zirconium alloys

Novel ZrB2-reinforced zirconium (Zr) alloys with different boron (B) and aluminum (Al) contents were produced by arc-melting technique. Microstructural observation indicated that both the α-lath and the prior-β grain size were significantly refined with increased B content. The thickness of α lath gradually increased with increased solute atom Al content. Compressive test results showed that the modulus and strengths of the alloys improved with increased ZrB2 and Al contents. The presence of abundant ZrB2 whiskers and solid solution atom Al were responsible for the increased Young׳s modulus. The strengthening mechanisms can be attributed to strengthening through load transfer between the ZrB2 whiskers and Zr matrix, morphological changes in alloys resulting from the formation of ZrB2 whiskers, and solid-solution strengthening caused by Al addition. Fractography confirmed that ZrB2 whiskers undertook the load transferred from Zr matrix and that crack sources were primarily generated at ZrB2 whiskers.

Effect of Li atom infiltration by the way of electro-osmosis on electrochemical properties of amorphous Mg65Ni27La8 alloy used as negative electrode materials for the nickel–metal hydride secondary batteries

The Mg65Ni27La8 alloy is synthesized by arc melting and subsequent melt-spinning technique, then Li atoms are infiltrated into this alloy material by the way of electroosmosis. The structure of the above two kinds of alloys is characterized by X-ray diffraction and scanning electron microscopy. Furthermore, electrochemical properties of two alloy electrodes are investigated systematically. Electrochemical studies indicate that negative electrode prepared by the Mg65Ni27La8-Li alloy possesses the best discharge capacity (693.8mAh/g) and cycling stability (83.2% after 30cycles) at a current density of 30mA/g, which is higher than that of Mg65Ni27La8 alloy electrode. Compared with the Mg65Ni27La8-Li alloy, the Mg65Ni27La8 alloy shows better discharge capacity of 571.9mAh/g and lower cycling stability (70.2% after 30cycles), which explains the structure evolution of amorphous ribbon that is responsible for the decay of discharge capacity. In addition, we also study the electrochemical reaction kinetics of Mg65Ni27La8-Li alloy electrodes.

Effect of Li on structure and electrochemical hydrogen storage properties of Ti55V10Ni35 quasicrystal alloy

The Ti55V10Ni35 quasicrystal ribbons are synthesized by arc melting and subsequent melt-spinning technique and then Li atoms are infiltrated into this quasicrystal material by the way of electroosmosis. X-ray diffraction results indicate that the pristine quasicrystal Ti55V10Ni35 mainly consists of the icosahedral quasicrystal (I-phase), V-based solid solution phase with BBC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some amount of Li atoms into Ti55V10Ni35 quasicrystal lattice voids at different electroosmosis current density (A/mg) of 0.3, 0.6 and 0.9 respectively, phase structure investigations show that the main phase structures do not change greatly except for the additional lithium phase, which demonstrates that Li does not destroy the phase structure of Ti55V10Ni35 quasicrystal. Ti55V10Ni35 alloy shows the best discharge capacity is 219.8 mAh g−1 at a current density of 30 mA g−1. The negative electrode made by Ti55V10Ni35–Li quasicrystal alloys (Li atoms are infiltrated into Ti55V10Ni35 quasicrystal alloy at different the electroosmosis current density (A/mg) of 0.3, 0.6 and 0.9 has a maximum discharge capacity of 257.7 mAh g−1, 301.8 mAh g−1 and 238.7 mAh g−1 at a discharge current density of 30 mA g−1, respectively. And the high rate discharge ability of alloy electrodes is higher than that of Ti55V10Ni35 quasicrystal alloy at 240 mA g−1. The Effect of Li on structure of Ti55V10Ni35 quasicrystal has been discussed by measuring the place, mass ratio and chemical state that Li infiltrated into quasicrystal Ti55V10Ni35 lattice. In addition, the electrochemical reaction kinetics of Ti55V10Ni35–Li quasicrystal alloy electrodes is also studied by measuring both the electrochemical impedance spectroscopy and hydrogen diffusion coefficient.

Electrochemical hydrogen storage properties of Ti1.4V0.6Ni quasicrystal and TiH composite materials

In this study, we use arc-melting and subsequent melt-spinning techniques to prepare Ti1.4V0.6Ni alloy ribbons. The Ti1.4V0.6Ni+xTiH (x=5, 10, 15 and 20wt.%) mixture powders are obtained by mechanical ball-milling. Also, we investigate the structure and electrochemical hydrogen storage properties of composite materials. Besides I-phase, FCC and BCC phase, the XRD of composite materials indicates it contains TiH phase. After adding TiH, the discharge capacities of Ti1.4V0.6Ni alloy electrode increase first and then decrease with increasing amount of Ti. The achieved maximum discharge capacity is about 339.8mAh/g (x=15wt.%) at the first discharge cycle. Additionally, composite materials lead to significant improvement in the high-rate dischargeability (HRD) as well as the cyclic stability.

Effect of Heat Treatment in Air on Thermoelectric Properties of Polycrystalline Type-I Silicon-Based Clathrate: Ba8Al15Si31

The effect of heat treatment in air on the thermoelectric properties was investigated for polycrystalline Ba8Al15Si31, where the Al content is almost at the maximum in the Ba8AlxSi46−x system, to evaluate the thermal stability in air at high temperatures, which is indispensable for practical use in thermoelectric applications. Samples were prepared by combining arc melting and spark plasma sintering techniques. Heat treatments were performed in air at 873 K for 10 days and 20 days. The Seebeck coefficient, electrical conductivity, and thermal conductivity were measured before and after the heat treatments. The microstructure and chemical composition were also analyzed before and after the heat treatments, using scanning electron microscopy with energy-dispersive x-ray spectroscopy. Although an oxidation layer was formed on the surface by the heat treatment in air, the chemical composition of the interior of Ba8Al15Si31 was found to be stable in air at 873 K for 10 days and 20 days. The Seebeck coefficient, the electrical conductivity, and the thermal conductivity were found to be almost unchanged after the heat treatment, indicating that Ba8Al15Si31 clathrate is promising as a thermoelectric material with high thermal stability for use in air at 873 K.

Mechanical properties and microstructure of in situ formed Ti2AlN/TiAl(WMS) composites

The Ti2AlN-reinforced TiAl (WMS) composites with different contents of Ti2AlN were prepared by an in situ method of reactive arc-melting technique. According to the results of X-ray diffraction (XRD) analysis, the Ti2AlN-reinforced WMS composites consist of γ-TiAl, α2-Ti3Al, and Ti2AlN phases. Microstructure analysis results indicate that Ti2AlN reinforcements with rod-like in shape form in the WMS matrix with a α2/γ lamellar structure containing some bulk γ phases. With volume fraction of Ti2AlN increasing, the grain size of the composites decreases significantly and the elasticity modulus (E) increases. The compressive strength and compressive fracture strain of the composite with 3 vol% Ti2AlN have a maximum value of 1,654 MPa and 22.5 %, respectively, which are approximately improved by 45.84 % and 29.31 %, respectively, compared with that of the unreinforced WMS alloy.

Microstructural evolution and mechanical properties of as-cast and directionally-solidified Nb-15Si-22Ti-2Al-2Hf-2V-(2, 14) Cr alloys at room and high temperatures

Arc-melting (AC) and directional solidification (DS) techniques were used to prepare Nb-15Si-22Ti-2Al-2Hf-2V-(2, 14) Cr alloys (hereafter referred as to 2Cr and 14Cr alloys, respectively), and the microstructural evolution and mechanical properties, including Vickers hardness, room temperature fracture toughness and high temperature strength, of the two AC and DS alloys were compared. The results showed that with heat-treatment at 1350 °C for 50 h, the AC-2Cr alloy composed of Nb solid solution (NbSS) and α-Nb5Si3 silicide, while Laves C15-Cr2Nb phase arose in the 14Cr alloy. With two-phase NbSS/α-Nb5Si3 microstructure, the AC-2Cr alloy showed excellent room-temperature fracture toughness (KQ: 14.2 MPa m1/2) and 0.2% yield strength at 1250 °C (σ0.2: 315 MPa) and 1350 °C (σ0.2: 294 MPa), better than the AC-14Cr alloy with tri-phase NbSS/α-Nb5Si3/C15-Cr2Nb microstructure (KQ: 9.4 MPa m1/2, σ0.2: 189 MPa at 1250 °C and 87 MPa at 1350 °C). The DS technique was found not to change the phase constituent of each alloy, but it made the microstructure slightly orient to the growth direction, resulting in a significant improvement in room-temperature fracture toughness (by ∼43%) and high-temperature yield strength σ0.2 (by ∼55%), as compared with the AC samples.

Yb-substituted clathratesBa8-xYbxGa16Ge30

Exploration of new rare-earth captured clathrates is an important field of clathrate application. Study on the second phases produced in the synthesis process is crucial for confirming the incorporation of rare earth atoms into the clathrate lattice. In the current study, the Yb -doped clathrate samples with nominal composition of Ba6Yb2Ga16Ge30were prepared by combining arc melting (ARC), melt spinning (MS) and spark plasma sintering (SPS) techniques. By using the TEM with EDS analysis and X-ray diffraction refinement, phase analysis was systemically performed in different steps of the preparation process. Although the clathrate was the main phase in obtained samples, the Yb content in the clathrate phase was found to be much lower than the nominal composition as the Yb atoms strongly tend to create other byproduct phases including Yb2O3— which is the main obstacle in the synthesis of Yb -substituted clathrates. For the dilute Yb -doped germanium clathrate sample a decrease in the thermal conductivity and electrical conductivity was simultaneously observed, therefore, no expected improvement of ZT occurred.

Physical properties of the layered compounds RE3Ru4Al12 (RE=La–Nd)

A series of ternary rare earth compounds RE3Ru4Al12 (RE=La–Nd) were synthesized by arc-melting technique, including the newly synthesized RE=La compound. X-ray diffraction measurements revealed that these compounds crystalize with the space group P 63/mmc. Magnetization, electric resistivity and specific heat of the samples were systematically measured. The results reveal that La3Ru4Al12 is Pauli paramagnetism while Ce3Ru4Al12 is intermediate valence. A ferromagnetic order is realized below about 40K for Pr3Ru4Al12 and Nd3Ru4Al12. The related study may contribute the further understanding about the electron correlated picture in the triangular layered structure compounds.

New structure in refractory high-entropy alloys

The microstructure of a new refractory high-entropy alloy of composition close to Ti35Zr27.5Hf27.5Nb5Ta5 prepared by arc melting and induction techniques was investigated using X-Ray diffraction (XRD) and transmission electron microscopy (TEM). This alloy presents optimal empirical parameters for the formation of a solid solution phase. The as-cast material displays a density of 8480kgm−3 and a Vickers microhardness close to 2400MPa. While the Rietveld refinement of XRD data indicates an orthorhombic (martensite) α׳׳-type structure for the bulk alloy, TEM observations prove that the alloy exhibits a twinned hexagonal structure as thin foil. An orthorhombic–hexagonal transformation by stress relaxation during TEM sample preparation is discussed.

Site-occupation behavior and solid-solution hardening effect of rhenium in Mo5SiB2

The site-occupation behavior of Re in Mo5SiB2 (T2) was studied both theoretically and experimentally, and the effect of Re on the solid-solution hardening of T2 was investigated by taking into account the off-stoichiometry of the T2 phase. Mo–Si–B quaternary alloys containing 1.4 at.% Re were produced using a conventional Ar arc-melting technique, and the cast samples were homogenized at 1800 °C for 24 h in an Ar atmosphere. High-resolution high-angle annular dark-field scanning transmission electron microscopy observations strongly suggest that Re preferentially occupies the Mo sites in the Mo–B layers of the T2 unit cell, which was confirmed by the site-occupation behavior predicted by first-principles calculations. Nanoindentation measurements indicate that the hardness of the T2 phase is affected by both the off-stoichiometry and Re addition.

Microstructure and hydrogen storage properties of (Ti0.32Cr0.43V0.25) + x wt% La (x = 0–10) alloys

The composite alloy of Ti0.32Cr0.43V0.25 with x wt% La (where x = 0–10) was prepared by arc melting technique. The effect on hydrogen storage capacity, flatness of the plateau pressure, and residual hydrogen was investigated in La added Ti0.32Cr0.43V0.25. Crystalline phase and microstructure of the prepared composite alloy were investigated and characterized by XRD, SEM and TEM. The crystal structure was refinement using Rietveld analysis. The effective hydrogen storage capacity of the composite alloy was found comparable to the parent alloy, when 5 wt% La was added. The effective hydrogen capacity (∼2.31 wt%) was close to that of the parent alloy (2.35 wt%) and the plateau slope was significantly improved from 30.5 of the parent alloy to 14.6. Appropriate mechanisms associated with the improved flatness by the La addition has been discussed in terms of the refined crystalline structure. Using TG/DTA method we have shown the differences in the interaction of residual hydrogen with the BCC phase of both parent alloy and 5 wt % La mixed alloy.

Microstructure of a near-equimolar refractory high-entropy alloy

The microstructure of a promising equimolar refractory high-entropy alloy containing Ti, Zr, Hf, Nb and Ta has been investigated after arc melting and induction techniques. The high-entropy alloy displays a fully disordered bcc crystal structure. At the nanoscopic scale, the observed dislocations appear mainly patterned in sub-grain boundaries in the solid solution. At the mesoscopic level and following the cooling rate, the solidified microstructure is different: the alloy exhibits a dendritic structure with the presence of Ti, Zr and Hf-rich microsegregations in the interdendritic zones for the slowest cooled parts, whereas it is fully homogenized in the regions for which the cooling rate is intense.

Growth of Oxide Nanotube Arrays on Ti-Ni Alloy

Ti-Ni alloys exhibit unique shape memory effect and superelasticity, which render them a wide range of applications in biomedical fields, such as dental and orthopedic as well as cardiovascular devices. However, it has been reported in-vivo implantation of Ti-Ni alloys caused corrosion after a few months. The corrosion will not only degrade mechanical properties of Ti-Ni alloys but also lead to the release of harmful Ni ion. In order to avoid this problem, many surface treatments have been proposed. In the present study, the growth of oxide layers on Ti-Ni alloys was examined using anodization.Materials examined were Ti-Ni alloys fabricated bya conventional arc melting technique. Anodization of Ti-Ni alloy was carried out in ethylene glycol containing 0.25wt.% NH4F and 1.5wt.% deionized water. The anodizations were carried out at various voltages at room temperature in a two-electrode configuration with a Ti-Ni alloy as a working electrode and platinum gauze as a counter electrode. After the anodization, the morphology, crystal structure, composition of the substrates and oxide layers formed were characterized.SEM observations revealed that the morphology of resulting oxide layers strongly depended on applied voltage and chemical composition of Ti-Ni alloy. Under optimized conditions it was found that tubular oxide layers could be formed on the substrates.

Influence of Annealing Conditions on Structure and Critical Parameters of Ni50Mn37Sn13 Magnetocaloric Material

In this paper, we present the influence of annealing conditions on structure and magnetic behavior of Ni\(_{50}\)Mn\(_{37}\)Sn\(_{13}\) magnetocaloric alloy prepared by arc-melting technique. The results show that the almost single phase of the full Heusler structure of Ni\(_{2}\)MnSn could be achieved by appropriate annealing. The transformation between martensite and austenite phases, and multi-magnetic phase behavior are observed more clearly with higher fraction of Ni\(_{2}\)MnSn phase. By using Arrott-Noaks method, critical parameters were determined to be \(\beta 0.464 \pm 0.021\), \(\gamma = 1.117 \pm 0.073\) and \(\delta = 3.41\), which lay between mean-field model (\(\beta = 0.5\) and \(\gamma = 1\), \(\delta = 3\)) with long-range ferromagnetic orders and 3D Heisenberg model (\(\beta = 0.365\), \(\gamma = 1.336\), \(\delta {\rm g}= 4.66\)) with short-range ferromagnetic orders. The calculated results are in good accordance with the experimentally observed coexistence of weak-ferromagnetic martensite and strong-ferromagnetic austenite phases.

First-principles computational design and synthesis of hybrid carbon–silicon clathrates

Type I and Type II silicon clathrates (Si46 and Si136), which can be considered as analogs of carbon fullerene materials, are composed with face-sharing Si20, Si24, and Si28 cages linked through sp3-covalent bonds. Besides silicon clathrates, theoretical computations have shown that both Type I carbon clathrate (C46) and Type II carbon clathrate (C136) may exist as metastable phases under high pressures. However, the energies of formation for the Type I and Type II carbon clathrates are extremely high and neither Type I nor Type II carbon clathrates have been synthesized. The objective of this investigation was to develop Type I hybrid carbon–silicon clathrates by substituting atoms on the silicon clathrate framework with C atoms. A first-principles computational approach was first utilized to design the framework structure and to identify appropriate guest atoms that are amenable to the formation of hybrid carbon–silicon clathrate compounds. A new class of Type I clathrates based on the carbon–silicon system was discovered as potential candidates. Some of the promising candidate clathrates were synthesized using an industrial arc-melting technique. The yield and stability of these newly discovered clathrates were evaluated. In addition, the electronic properties of selected clathrate materials were predicted using first-principles computations, which showed profound influences of the electronic properties by C atom substitution on the Si framework and insertion of guest atoms into the cage structure.

Evolution of Helium with Temperature in Neutron-Irradiated10B-Doped Aluminum by Small-Angle X-Ray Scattering

Helium status is the primary effect of material properties under radiation.10B-doped aluminum samples were prepared via arc melting technique and rapidly cooled with liquid nitrogen to increase the boron concentration during the formation of compounds. An accumulated helium concentration of ~6.2 × 1025 m−3was obtained via reactor neutron irradiation with the reaction of10B(n,α)7Li. Temperature-stimulated helium evolution was observed via small-angle X-ray scattering (SAXS) and was confirmed via transmission electron microscopy (TEM). The SAXS results show that the volume fraction of helium bubbles significantly increased with temperature. The amount of helium bubbles reached its maximum at 600°C, and the most probable diameter of the helium bubbles increased with temperature until 14.6 nm at 700°C. A similar size distribution of helium bubbles was obtained via TEM after in situ SAXS measurement at 700°C, except that the most probable diameter was 3.9 nm smaller.

Microstructure Characteristics and Mechanical Properties of <i>In Situ</i> TiB/Ti Composites Prepared by Arc-Melting Technique

In this paper, in situ TiB reinforced Ti-3Al, Ti-6Al and Ti-6Al-4V matrix composites were prepared by arc-melting technique utilizing the reaction between Ti and TiB2, and then forged in the α+β phase field. Phase identification was carried out via X-ray diffraction. Microstructure of the composites was studied by optical microscopy (OM) and scanning electron microscopy (SEM). Mechanical properties of the composites after forging were measured at various temperatures by tensile experiment. The results showed that Ti-6Al-4V-2TiB composite exhibits fine equiaxed matrix microstructure with a grain size of 5-10μm. The tensile strength and elongation of the composite at room temperature reached 1069MPa and 10.0%, respectively.

Effect of Ti on the microstructure and Al–water reactivity of Al-rich alloy

Ti-bearing Al alloys (0.1–1 wt.%) were prepared using arc melting techniques. Their microstructures were investigated using XRD and SEM/EDX, and found to depend strongly on Ti contents. Al grains are columnar as Ti contents are lower, but they are refined and turn into equiaxed ones when Ti contents are higher. The particle sizes of Ga–In–Sn phase decrease with Al grain refinement. Al–water reactivities were also investigated under different water temperatures. Kinetic measurements found that Ti prohibits Al–water reaction and reduces hydrogen yields when alloys contain little Ti. However, Al reacts with water fast and hydrogen yields rise with the increase of Ti contents of alloys. Reasons concerning the variations of microstructures and Al–water reactivities with Ti additions are discussed.

Synthesis and thermoelectric properties of rare earth Yb-doped Ba8−xYbxSi30Ga16 clathrates

The potential thermoelectric and magnetic application of clathrate materials with rare-earth doping is the focus of much of the recent research activity in the synthetic material physics and chemistry. A series of clathrate samples with the chemical formula Ba8−xYbxSi30Ga16 (x=0, 0.5, 0.7, 1 and 1.5) were prepared by combining arc melting, ball milling and spark plasma sintering (SPS) techniques. X-ray diffraction and scanning electronic microscopy combined with energy-dispersive X-ray spectroscopy (EDS) analysis showed the dominant phase to be the type-I clathrate. Whereas, X-ray structural refinement and EDS analysis indicated that some Yb atoms enter the clathrate lattice to replace Ba at 2a sites, while other Yb atoms are oxidized as Yb2O3 precipitated around grain boundaries. The solid solubility of Yb into clathrate lattice yielded x∼0.3. Comparative analysis between Yb-doped and Yb-free clathrates showed that the thermal conductivity decreases with Yb-doping. Consequently, thermoelectric figure of merit ZT significantly increased.