Pendant Drop Melt Extraction Research Articles

Production of multi-principal-component alloys by pendent-drop melt extraction

In order to examine the influence of the production technique on the performance of hydride-forming multi-principal-component alloys, a series of alloys in the Ti–Zr–V–Nb–Ta-Hf system has been obtained by arc-melting and electron beam melting combined with pendant-drop melt extraction (EBM-PDME). Structure analysis shows that EBM-PDME method ensures the synthesis of single-phase alloys with BCC structure for all studied compositions. During hydrogenation, the complete and reversible BCC to FCC phase transformation with maximum hydrogen capacity up to 2.0 wt% occurs. Mechanical and thermophysical investigations demonstrate high values of tensile strength, plasticity and thermal conductivity, which allow the alloys to be used as materials for membrane hydrogen separation.

Composition design, synthesis and hydrogen storage ability of multi-principal-component alloy TiVZrNbTa

A thermodynamic model was proposed to assess the feasibility of the synthesis of single-phase multi-principal-component alloy. Based on this model, single-phase TiVZrNbTa equiatomic alloys with body centered cubic (BCC) structure were obtained by arc melting (AM), electron beam melting with pendant drop melt extraction (EBM-PDME) and mechanical alloying (MA). The alloys were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, thermal analysis and mechanical testing. The hydrogenation behavior of the synthesized materials was studied by a volumetric method. It was found that for AM and EBM-PDME alloys a complete BCC-to-FCC structure transformation occurs upon hydrogenation, and hydrogen concentration in the hydrides formed reaches 1.5 H/M (1.6 wt%). MA alloy undergoes partial amorphization with maximum hydrogen absorption capacity of 0.9 wt%.

Obtaining and plasma-electrolyte modification of fibers of ultralight magnesium alloy

The results of researches for the transformation to fiber state the Mg-8Li-1Al-0.6Ce-0.3Y ultralight magnesium alloy by the Pendant Drop Melt Extraction (PDME), and subsequent modifying obtained fibers by Plasma-Electrolytic Treatment (PET) are presented. The results demonstrate possibility of successful application of the above-mentioned methods in relation to chemically active materials. Purposeful modifying of ultralight magnesium alloys by PDME and PET methods is capable to significantly expand areas of using to these materials.

Structure and properties of Ta-Zr alloy obtained by high-speed melt quenching from liquid state

The paper considers the effect of Ta-Zr binary system splat quenching implemented by the method of pendant drop melt extraction. The study was conducted using two mixtures of tantalum and zirconium elementary powders with a content of 60 and 6 % of tantalum respectively. After mixing, the compositions were pressed at 250 MPa in a steel mold on a hydraulic press. Sintering was carried out in a vacuum furnace at 1350 °C and a pressure of 10-3 Pa. Splat quenching was carried out in a vacuum at 2•10-2 Pa using electron-beam heating and a spinning disk absorber. Resulting fiber thickness was 15 to 80 gm. The results of testing splat-quenched Ta—Zr alloy discrete fibers and samples formed as a result of rod stock melting by electron-beam heating (as-cast) were studied and compared. It was found that the structure of splat-quenched fibers of the alloy with a Ta content of 6 wt.% consists of 5—10 gm needle-shaped grains, and the alloy with a Ta content of 60 wt.% has a columnar dendritic structure. A study of tantalum and zirconium distribution across the fiber cross-section showed that cooling rate reduction to less than 105 K/s leads to monotectoid transformation in the alloy with a tantalum content of 60 wt.%. It was found that for an alloy with 6 wt.% Ta the fiber microhardness value is 1.5 times higher in comparison with the same alloy without quenching, and for an alloy with Ta 60 wt.% it is higher by a factor of two.

Exchange bias and spin-reorientation transition in α-Fe/PrDyCoFeB core/shell microwires

Magnetic anisotropy and interface exchange interaction were analyzed in α-Fe core microwire covered with PrDyCoFeB amorphous shell. The α-Fe/PrDyCoFeB core/shell microwires were grown by pendant drop melt extraction technique providing separation of the α-Fe and PrDyCoFeB phases during the ultrafast cooling. Low saturation field of the core ~100 Oe and high saturation field of amorphous shell ~10 kOe with zero coercivity were distinguished from angular dependences of the magnetic moment, recorded in low and high magnetic fields. Sharp decrease of the longitudinal magnetization, effective anisotropy field and magnetic susceptibility have been observed below the critical temperature, Tcrit = 240 K, in zero field. The Almeida-Thouless transition from ferrimagnetic state to Ising spin glass state has been revealed in PrDyCoFeB amorphous shell. Such spin reorientation transition is very attractive for magnetocaloric applications. We found exchange bias effect controlled by exchange coupling between ferromagnetic core and ferrimagnetic shell. The significance of the obtained data lies in possible applications of the core/shell microwires for tweezers with magnetic moment, stepwise changing in external field. Exchange bias in core-shell interface provides determined initial state of the microwire used as working media of field sensor. The sharp decrease of the magnetization associating with spin-reorientation transition looks very promising for magnetocaloric applications close to room temperature.

Role and behavior of ultra-thin gold films on the fiber materials surface in the CO oxidation process

The work continues a series of studies aimed at enhancing catalytic properties of metal fibers formed by the pendant drop melt extraction (PDME) method. In this paper, we show that deposition of the thin gold film on the metal fibers leads to a change in the catalytic performance of the samples under study. Au-coated fibers of titanium, zirconium and alloys of the Fe–Cr–Al, Ni–Cr–Al–Y, Ni–Cr–Al–Pt–Ir–Hf, Ni–Cu–Fe–Mn systems were tested as catalysts in the reaction of CO oxidation. We have found that the deposition of gold makes titanium, zirconium, and Fe–Cr–Al fibers catalytically active, while in the initial state they have not shown any evidence of catalytic activity. In the case of Ni–Cu–Fe–Mn fibers, which could oxidize CO themselves, the deposition of Au film significantly increases their catalytic properties. It was found that during the catalytic process, gold film coalesces to droplets with the predominant size of 11–14 nm.

Морфология и механические свойства микропроводов PrDyFeCoB

PrDyFeCoB microwires were obtained by pendant drop melt extraction (PDME). The diameter and cylindricality of microwires are controlled by the rotation speed of the cooling cylinder and depend on the solidification time of the drop on it. Variations in the cooling regime of the melt drop lead to a change in the shape of the cross section from a completely cylindrical to a semicircle, a crescent, and an almost flat plate. It was established that the cooling mode affects not only morphology, but also mechanical characteristics that are different for microwires of different shapes, and also changes the microhardness and Young's modulus of different surfaces of the same microwire.

Plasma-electrolytic treatment of magnesium alloy fibers

The results of researches of the modifying effect of the Pendant Drop Melt Extraction (PDME) and the Plasma-Electrolytic Treatment (PET) methods for ML10 magnesium alloy are presented. Particularities of PET for fibrous magnesium alloy are studied. Metallography, morphology analysis and corrosion tests are executed. The conclusion that application of the PET and PDME methods for purposeful modifying is capable to significantly expand possibilities of magnesium alloys using was made.

Core-shell ferromagnetic microwires extracted from PrDyFeCoB and GdPrDy(FeCo)B melts

The α-Fe core/PrDy-FeCo-B(48 at.%)α-Fe(52 at.%) shell and GdPrDy(FeCo)B microwires were grown by pendant drop melt (PDM) extraction technique. Single core–shell microwires of ~80–100 μm diameter and 2–20 mm length manifest rectangular hysteresis loops corresponding to ~100 Oe switching magnetic fields. Bistability of the microwires relates to single domain state of the α-Fe inner core revealed by scanning electron microscopy (SEM). Rare-earth amorphous PrDy-FeCo-B shell of the microwire scanned by magnetic force microscope (MFM) possesses magnetization reversal nuclei corresponding to the α-Fe inclusions. Interwire magnetic dipole interaction and scattering of microwire size change shape of the magnetic hysteresis loop and increase coercive field up to 983 Oe, in chaotic ensembles of the core–shell microwires. The GdPrDy(FeCo)B microwires of the same sizes with no Fe core possess “butterfly” type of the hysteresis loop of high coercivity ~20 kOe.

Modifying of magnesium alloys for creation of effective electrochemical power sources

The results of researches of the modifying effect on magnesium alloy of the Microarc Discharge Oxidation (MDO) and the Pendant Drop Melt Extraction (PDME) methods are presented. The possibility of changing in electrochemical activity and in specific surface value for the electrodes materials that apply to creation of electrochemical power sources is shown.

Effect of сopper сoating on fibers made of aluminum alloy, titanium, and FeCrAl alloy on surface morphology and activity in CO oxidation

The catalytic activity of both copper fibers and copper-coated fibers of a diameter of 50–100 μm made of aluminum alloy, technical grade titanium, and FeCrAl alloy in CO oxidation has been estimated. Metal fibers have been fabricated by the method of pendant drop melt extraction (PDME). The fibers copper plating was carried out by chemical and electrochemical methods. The composition and structure of samples and coatings before and after catalytic tests have been characterized by the methods of scanning electron microscopy, energy-dispersive analysis, and X-ray fluorescence analysis. It has been shown that the catalytic activity of copper-coated fibers made of FeCrAl alloy in the reaction of CO oxidation is not inferior to that of copper fibers.

Forming porous fibrous materials by the pendant drop melt extraction

A method for forming porous material based on metallic fibers, which are obtained by pendant drop melt extraction (PDME) method, is proposed. An installation for forming porous fibrous materials by the PDME method is developed and fabricated. Samples of porous materials made of fibers of heat-resistant and corrosion-resistant steels, nickel alloys, zirconium, etc., are obtained. Mechanisms for forming the bonds between the fibers are investigated and an interaction model between the fibers in a formed material is proposed. The possibility of forming bonds between the fibers in a porous material based on copper and steel fibers at various extraction velocities is evaluated according to the proposed model.

Causes of wavelike variation in the cross section and breaking of fibers obtained by pendant drop melt extraction

The causes of emergence of wavelike variations in the cross section of metal fibers obtained by pendant drop melt extraction on a cold rotating wheel in vacuum are analyzed. The theoretical results are confirmed by experimental data for fibers made from aluminum and the VT1 titanium alloy. It is shown that the variation in the diameter and fiber breaking are caused by capillary waves (Rayleigh waves) on the surface of the melt drop, which are induced by rotation of the cold rotating wheel. The waves at the fiber surface apparently emerge under the effect of vibrations with frequencies higher by a factor of 3000–3500 compared with the rotation speed of the wheel or by the defects located on the fiber surface at a distance of ∼0.2–0.3 mm from each other.

Adhesion interaction on melt extraction from pendant drop

A technique of pendant drop melt extraction (PDME) is reported and certain results describing thin stainless steel fibers obtained by means of PDME were studied. Adhesion interaction between metal melt and disc-crystallizer was also considered. The adhesion work was established to be approximately 1–2 J/m 2. It was shown that melt adhesion to the disc-crystallizer is determined both by physical interaction and chemical processes in contact region.

Bi2Sr2CaCu2O8 fibers spun by means of pendant drop melt extraction

Abstract Fibers of Bi 2 Sr 2 CaCu 2 O 8 up to 15 cm in length have been spun by means of pendant drop melt extraction; typical diameters are 60 μm. The fibers, as-spun, are amorphous, flexible, and not superconducting; they can be made superconducting by a subsequent heat treatment. Fibers heat-treated in air at 850°C for 72 h have a T c of 80 K, measured magnetically; at 4.2 K they have intragranular critical current densities on the order of 10 6 A/cm 2 at 1 T, and transport critical current densities of typically 100 A/cm 2 in zero field. The fibers after heat treatment are very brittle.

Fibers of YBa 2 Cu 3 O 7 by pendant drop melt extraction

Abstract Fibers of YBa 2 Cu 3 O 7 have been produced by pendant drop melt extraction, a technique in which the end of a rod of YBa 2 Cu 3 O 7 is melted with a hydrogen-oxygen torch and lowered onto the edge of a spinning wheel. Fibers up to 10 cm in length have been produced; usually the lateral dimensions were in the range from 20 to 125 μm. The fibers required a heat treatment to make them superconducting; the T c of heat treated fibers ranged from 88 to 90 K.

The influence of Nb addition on structure and properties of rapidly solidified intermetallics

The intermetallic alloys Ti-15wt.%Al-7wt.%Cu, Ti-15wt.%Al-7wt.%Cu-10wt.%Nb and Ti-15wt.% Al-14wt.%Cu were vacuum arc melted followed by rapid solidification by the pendant drop melt extraction technique in vacuum. A detailed characterization of these rapidly solidified materials was conducted using light optical microscopy, scanning electron microscopy-energy dispersive spectroscopy, microhardness, bend ductility tests, scanning transmission electron microscopy, X-ray diffraction and differential thermal analysis. The presence of niobium improved chemical homogeneity of the copper and alluminum and refined the microstructure, resulting in improved ductility at room temperature.

Beta-Eutectoid decomposition in rapidly solidified titanium-nickel alloys

The eutectoid reaction, β → α + Ti2Ni, has been observed in as-produced rapidly solidified ribbons and flakes of hypoeutectoid and near-eutectoid beta titanium-nickel alloys prepared by chill block melt spinning (CBMS), pendant drop melt extraction (PDME), and electron beam melting/splat quenching (EBSQ) processes. Microstructural characterization of these materials was carried out by scanning electron microscopy, transmission electron microscopy, and X-ray energy dispersive spectroscopy. The occurrence of eutectoid decomposition in the rapidly solidified alloys was attributed to the breakaway of the ribbons or flakes (while still at an elevated temperature) from the quench wheel, resulting subsequently in a lower cooling rate. Fast quenching, as obtained in the hammer-and-anvil process, resulted in a martensitic structure free from products of eutectoid decomposition. The eutectoid morphology was nonlamellar in hypoeutectoid alloy ribbons, while a hitherto unreported lamellar eutectoid was observed in the near-eutectoid ribbons and flakes. The formation of this unusual lamellar eutectoid was rationalized in terms of the predominance of allotriomorphs of alpha phase and consequent availability of sufficiently mobile and maneuverable alpha/beta interphase boundaries in the fine-grained, rapidly solidified titanium-nickel alloys.

Microstructures and Thermal Properties of Rapidly Solidified Aluminum-Rare Earth Alloys

ABSTRACTRapidly solidified (RS) Al-Er, Al-Nd, and Al-Gd ribbons were prepared by pendant drop melt extraction (PDME). The microstructures were studied in detail by optical and transmission electron microscopy. A wide range of microstructures are observed, including “conventional” RS type zones, a cellular structure surrounded by a degenerate eutectic and coupled (lamellar) eutectic structures. A bimodal precipitate distribution is seen in many areas of the ribbons. A series of isochronal heat treatments was conducted to determine the relative thermal stability of these microstructures, which were evaluated by Knoop microhardness measurements.

Microstructures of Rapidly Solidified Titanium-Eutectoid Former Alloys

ABSTRACTTitanium-base binary alloys containing eutectoid forming additions such as Fe, Si, W, and Cr were rapidly solidified by pendant drop melt extraction, melt spinning, and “hammer and anvil” techniques. The materials obtained were fibers, ribbons, and splats, respectively. The microstructures of these rapidly solidified materials were analyzed by optical microscopy, SEM, and TEM. The fibers showed fine microstructures near the quenched side, but less homogeneous and coarser microstructures were observed away from this side. Similar variations were observed between the edge and the center of splats. The results of this microstructural characterization are discussed, and a comparison made between microstructures obtained by the different rapid solidification methods used.