Rapid Solidification Technique Research Articles

Ultrafine Eutectic-Dendrite Composite Bulk Fe-B Alloy with Enhanced Ductility

that the yield strength and plasticity of Fe88Nb12 alloy were 1.4 GPa and 13.0%, respectively. Yield strength of 1.8 GPa and plasticity of 6.7% in the case of the Ti65Fe35 was obtained by Louzguine et al. 14) In summary, the structure of dendrite-ultrafine/nano composite can enhance the ductility of ultrafine/nano-structured materials. So, the dendrite-ultrafine/nano-structured Fe-B alloy was designed in this paper, which was expected to obtain high ductility. So far, there are only a few reports on the mechanical properties of the ultrafine/nano-structured Fe-B alloys. However, the mechanical behavior of the Fe-B alloys has important impact on industrial applications. In this letter, the dendrite-ultrafine eutectic composite Fe2B and Fe3B alloys were prepared by a self-propagating high temperature synthesis (SHS) combining rapid solidification technique. We investigated the relationship between the dendrite contents in the composite structure and the mechanical behavior. A small quantity of dendrites embedded in the ultrafine eutectic matrix can reinforce the ductility obviously. However, the ductility reduces when the content of dendrite is up to 90%. 2. Experimental Procedure The bulk Fe2B and Fe3B hypereutectic alloys were cast into a fully dendrite-ultrafine eutectic composite structure by a combination route of SHS processing and rapid solidification technique. This method was depicted in other literatures. 15–18) The polished cross sections were investigated by X-ray diffractometry (XRD, Philips X’pert) using

Relation between corrosion behavior and microstructure of Mg–Zn–Y alloys prepared by rapid solidification at various cooling rates

The relation between corrosion resistance and microstructure of Mg–Zn–Y alloys with a long period stacking ordered (LPSO) phase has been investigated. In order to clarify the influence of microstructure evolution by rapid solidification on the occurrence of localized corrosion such as filiform corrosion, several Mg 97.25Zn 0.75Y 2 (at. %) alloys with different cooling rates were fabricated by the gravity casting, copper mould injection casting and melt-spinning techniques and their corrosion behavior and microstructures were examined by the salt immersion tests, electrochemical measurements, XRD and TEM. When the cooling rate was less than 3 × 10 4 K s −1, filiform corrosion propagated in the early stage of salt immersion test, due to formation of a massive block-shaped LPSO phase during casting. On the other hand, when the cooling rate was increased up to 3 × 10 4 K s −1, rapidly solidified (RS) alloys exhibited excellent corrosion resistance because of grain refinement and formation of a supersaturated single-phase solid solution. Large-sized Mg 97.25Zn 0.75Y 2 alloys fabricated by consolidation of the RS ribbons also exhibited excellent corrosion resistance with passivity. Enhancement of microstructural and electrochemical homogeneities in the Mg–Zn–Y alloys by rapid solidification techniques results in the passivity of substrate materials.

Development of Ni-Mn-Ga Based Ferromagnetic Shape Memory Alloy by Rapid Solidification Technique

Rapid solidification route by melt spinning has been adopted for preparation of a Ni52.5Mn24.5Ga23 (at %) ferromagnetic shape memory alloy in the form of ribbons. In the as-spun state, the ribbon revealed a predominant austenitic L21 structure in combination with martensitic feature as observed from x-ray diffraction studies. Transmission electron microscopic (TEM) evaluation showed these features in the form of martensitic plates. At low temperature, martensite to austenite transformation was exhibited by an increase in magnetization during heating cycle. The reverse effect was observed during cooling cycle. Annealing temperature and magnetising field was also found to effect this transformation.

An approach to the bulk textured Fe81Ga19 rods with large magnetostriction

Bulk textured Fe81Ga19 alloy with large magnetostiction of up to 830ppm is fabricated using the technique of rapid directional solidification by triggering the undercooled Fe81Ga19 melts. The saturation magnetostriction is about two times as large as the maximum of the earlier report on Fe–Ga bulk samples. The large magnetostriction is ascribed to the high concentration of Ga–Ga atom pairs created by rapid solidification and their preferential orientation in the [100] textured rod.

Magnetostatic coupling in soft/hard biphase magnetic systems based on amorphous alloys

We report on magnetic bias in biphase systems arising from by dipolarlike interaction. Composites consist of amorphous ribbons and wires prepared by rapid solidification techniques, surrounded by an electroplated layer. Amorphous metallic core is (Co0.94Fe0.06)72.5Si12.5B15 with ultrasoft magnetic behavior (coercivity of 10–10−1A∕m), and the electroplated coating is crystalline Co85Ni15 alloy with harder magnetic character (coercivity of 104A∕m. After premagnetizing in a dc saturating field (106A∕m), the low-field (±103A∕m) hysteresis loops are ascribed to the magnetization process of the soft core and exhibit a typical shift towards the direction of the premagnetizing field. This shift is ascribed to the magnetostatic field generated by uncompensated poles at the edges of the hard layer, which remains close to its remanence state. The influence of the geometry of both phases on magnetostatic energy term allows us to tailor the bias field and susceptibility of the core. These results open other possibilities to use these materials as sensing elements in magnetic sensor.

Growth characteristic of Al 2O 3/Y 3Al 5O 12 (YAG) eutectic ceramic in situ composites by laser rapid solidification

Directionally solidified ceramic eutectic in situ composite as a candidate for a high-temperature structural material has attracted considerable attention and various preparation techniques have been developed. In this study, pore-free eutectic ceramics of Al 2O 3/Y 3Al 5O 12 (YAG) are prepared from melt by laser rapid solidification technique in order to investigate the microstructure characteristic and solidification behavior which are considered to be important factors influencing the properties of eutectic materials. The results show that: (1) The Al 2O 3/YAG eutectic displays a “Chinese script” structure, and faceting is the most important factor to determine the formation of the irregular eutectic morphology. (2) The scanning rate and power density of the laser beam are the most primary technological parameters affecting the eutectic microstructure. The eutectic spacing is extremely fined due to the high-temperature gradient and solidification rate, and decreases with the increase of the scanning rate and the average is only around 1 μm. (3) Elongated colonies with the periodic distribution are observed in the solidified eutectic due to the high destabilization of solid–liquid interfaces caused by the ununiformity of the laser heat-flux distribution when the scanning rate is higher than 2000 μm/s.

Magnetostatic bias in soft/hard bi-phase layered materials based on amorphous ribbons and microwires

Bi-phase soft/hard magnetic systems have been prepared by electroplating CoNi alloy with relative hard magnetic character (102Oe coercivity) onto ultrasoft (coercivity less than 1Oe) FeCo-based amorphous alloys prepared by rapid solidification techniques. Experiments have been performed in planar (ribbons) and cylindrical (microwires) configuration. Low-field hysteresis loops after premagnetizing to saturation are ascribed to the magnetization reversal process of the soft inner phase, while harder component remains close to its remanence. Such low-field loops exhibit a shift typical of magnetic bias phenomena which in this case is ascribed to the magnetostatic coupling originated through the stray fields created by uncompensated charges at the ends of the harder phase.

Effect of Salt Additives to Water on the Severity of Vapor Explosions and on the Collapse of Vapor Film

We proposed ultra rapid solidification and atomization technique, CANOPUS (Cooling and Atomizing based on NOble Process Utilizing Steam explosion), using small-scale vapor explosions to make an amorphous metal. The CANOPUS method is suitable for rapid cooling and atomization process, which utilizing sustainable small-scale vapor explosions. In order to apply the CANOPUS method to a high melting point metal, it is necessary to make a small-scale vapor explosion occur at a high temperature of the molten metal. Small-scale experiment is conducted to develop the vapor explosion promotor in which spontaneous vapor explosion can occur at a high temperature of a molten metal. Spontaneous vapor explosion do not occur when water at 80 o C is used as a coolant. However, spontaneous vapor explosion occurs when water at 80 o C with salt additives is used as a coolant. Specifically, lithium chloride solution generates spontaneous vapor explosions at the highest temperature of the molten tin in the experiment. In order to clarify the triggering mechanism of the spontaneous vapor explosion when the promotor is used as a coolant, a high-temperature solid stainless steel sphere is immersed into a coolant. The interfacial temperature of the stainless steel sphere is measured, and the behavior of a vapor film around the stainless steel sphere is observed with a digital video camera. As a result, salt additives resulted in an increase of quench temperature in all salt solutions. The quenching curves of each coolant indicate that the salt additives improve the film boiling heat transfer. The improvement of the film boiling heat transfer causes an unstable formation of the vapor film and a rise of the quench temperature. It is clarified that the salt additives to water promotes a vapor film collapse. Comparing two experiments, the quench temperature of each solution is in close agreement with the upper limit of the molten tin temperature that causes spontaneous vapor explosion. This result suggests that the vapor film collapse triggers spontaneous vapor explosion.

Critical cooling rate for the glass formation of ferromagnetic Fe 40Ni 40P 14B 6 alloy

Bulk ferromagnetic amorphous Fe–Ni–P–B alloys in rod shape were formed by a rapid solidification technique. The largest amorphous specimen prepared had a diameter of ∼ 2.5 mm and the corresponding cooling rate for the glass formation of this alloy system in our experiment can be estimated to be around 492.4 K/s by the method of finite-difference numerical calculation. This value is on the same order of magnitude as the critical cooling rate R c of Fe 40Ni 40P 14B 6 alloy estimated by the method of constructing the continuous-cooling-transformation (CCT) curve. It is indicated that the heterophase impurities have been eliminated well in our experiment.

Crystallization processes in Fe–Pt–Nb–B melt spun ribbons

Intermetallic Fe–Pt–Nb–B alloys with 3 different compositions have been synthesized by rapid solidification technique and their phase structure was characterized by means of X-ray diffraction and Mössbauer spectrometry. It is shown that Fe68Pt21Nb2B9 and Fe65Pt25Nb2B8 as-cast samples consist mainly of A1 soft magnetic f.c.c. Fe–Pt phase, while the Fe68Pt13Nb2B17 as-cast sample exhibits topological short-range order, typical for amorphous ribbons. Crystallization processes in the amorphous sample and phase evolution with the temperature have been studied using differential scanning calorimetry (DSC). The occurrence of exothermic peaks is related to structural transformations in the alloys and the crystallization process is shown to be highly dependent upon the heating rate in the DSC process.

Capillary stability limits for liquid metal in melt spinning

Single roll planar-flow melt spinning (PFMS) is a rapid solidification technique for producing thin metal sheets or ribbons. The key physics occur in a liquid metal puddle (bead) held by capillarity between the entry nozzle and a rotating metallic wheel. We present a semi-empirical analysis that (1) provides a theoretical basis for a previously reported empirical stability window, and (2) predicts an extension to the stability limits by adjusting the pressure outside the upstream meniscus relative to the pressure outside the downstream meniscus. A device capable of altering this pressure has been constructed and demonstrates extended operability.

Microstructures in rapidly solidified AISI 304 interpreted according to phase selection theory

The objective of this work is to use laboratory rapid solidification techniques to predict microstructures in AISI 304 produced during industrial processes. Two quenching methods have been employed to obtain a wide range of undercooling and microstructures: single roller melt spinning onto a copper wheel and casting into a conic mould. The experimental results are compared with theoretical predictions by using appropriate thermophysical parameters for the melt calculated with Thermocalc software while the dendrite tip temperature for ferrite and austenite phases is computed within the phase selection theory by means of a code written in MATLAB language.

Structural properties and evaluation of crystal fraction by cryogenic heat capacity measurements of Fe-based nanocrystalline alloy

An amorphous Fe 73.5Cu 1Nb 3Si 13.5B 9 alloy was prepared by the rapid solidification technique. The rapidly quenched alloys have been annealed in the temperature range from 490 to 550 °C for 90 min and their structure was investigated by using X-ray diffraction (XRD). After annealing, at crystallization temperature, the microstructure of the samples composed of nanocrystalline Fe 3Si grains surrounded by the residual amorphous phase. The crystal fractions of the annealed samples were evaluated by heat capacity measurements. Heat capacities of the as-quenched and annealed samples were measured at different temperatures between 15 and 40 K. This method is useful for evaluating small changes in the amount of crystalline phase and provides a new tool for finding the nanocrystalline fraction. The volume fraction of the crystalline phase increased from 15.92 to 94.21% as annealing temperature increased from 490 to 550 °C.

Shape memory properties of Cu-based thin tapes obtained by rapid solidification methods

Two different rapid solidification techniques were utilized to produce thin tapes of Cu–13Al– xNi–1Ti (wt.%, with x = 5, 5.5, 6) shape memory alloys directly from the melt. Both melt-spinning and twin-roll casting (quenching between the gap of two rollers) have resulted successful methods to obtain ribbons (8 mm width, 55 μm thickness) and strips (29–30 mm width, 450 μm thickness) with grain sizes below 2 μm, after optimization of the processing parameters. Although as a consequence of the rapid solidification the martensitic transformation temperatures are depressed, after annealing at 700 °C the high transition temperatures of the alloys in the bulk form are re-established. Measuring of length change under uniaxial tensile load shows elongations up to 1.8% (at 90 MPa) on cooling through the martensitic transformation.

The Impact of the Addition of Rare Earth Elements to Si1 − xSnx Negative Electrode Materials for Li-Ion Batteries

The impact of the addition of cerium and lanthanum-rich misch metal (MM, a mixture of rare earth elements) to silicon-tin alloys was studied using combinatorial and high-throughput materials science methods. Combinatorial libraries of , , and were prepared using the Dalhousie University combinatorial sputtering systems. The addition of MM increases the crystallization temperature of amorphous alloys, which makes their preparation in the amorphous state more likely by rapid solidification techniques like melt-spinning. Increasing the atomic fraction of MM in both and amorphous alloys decreases the reversible specific capacity of the alloys for lithium, but does not negatively impact capacity retention. Attractive compositions were identified in pseudoternary system that: (1) remain amorphous during charge-discharge cycling between 0.005 and vs ; (2) show excellent capacity retention; (3) have specific capacities as large as ; and (4) may be compatible with rapid solidification techniques for the production of amorphous materials. In particular, amorphous alloys containing tin and MM exhibited excellent capacity retention and reversible specific capacities near .

Shape memory thin round wires produced by the in rotating water melt-spinning technique

Rapid solidification techniques have been shown to be suitable for producing semi-finished shape memory alloys, as thin ribbons with good functional properties obtained by the planar flow melt-spinning method. We applied the in rotating water melt-spinning technique to produce thin round wires directly from the melt. Good results have been obtained for Cu–Al–Ni and Cu–Al–Ni–Ti–Cr alloys in the diameter range from 100 to 250μm. However, these wires can still present some surface irregularities, depending on the parameters of the process. All wires including those that are not well optimized exhibit good shape memory properties, both for uniaxial elongation and bending. When biased by a constant uniaxial tensile stress, an elongation up to 2% (at 70MPa) is attained on cooling below the martensitic transformation, completely recovered on heating. The transformation temperatures of the as-prepared wires are depressed in relation to those of the bulk alloys annealed at 850°C and quenched, as is observed for melt-spun shape memory ribbons. The temperatures of the wires and bulk alloys evolve in rather parallel ways upon ageing in air at moderate temperatures (250°C); thus a difference of about 20 or 50°C for the ternary and quinternary alloys, respectively, persists in the transformation temperatures between wires and bulk, due to the finer microstructure of the wires. The ageing treatment also causes a degradation of the shape memory properties; after a treatment for 700h at 250°C, the recoverable elongation under 70MPa is reduced to 1.2%.

Microstructure, electrical, mechanical and thermal properties of melt-spun bismuth–tin eutectic alloy

Microstructure, electrical, mechanical and thermal properties of melt-spun Bi58Sn42 eutectic alloy have been investigated using scanning electron microscopy, X-ray analysis, the double bridge method, dynamic resonance method, Vickers hardness measurement and thermal analysis. The structure and physical properties of this alloy are affected by the preparation method (rapid solidification technique). The bismuth–tin eutectic alloy has good properties as a lead-free solder alloy, such as low melting point and adequate cost and mechanical properties when compared with commercial tin–lead solder alloys.

Effect of Oxygen Content on Thermoelectric Properties of n-Type (Bi,Sb)<SUB>2</SUB>(Te,Se)<SUB>3</SUB> Alloys Prepared by Rapid Solidification and Hot-Pressing Techniques

Influence of oxygen content on the microstructure and thermoelectric properties of bismuth-telluride based (Bi,Sb) 2 (Te,Se) 3 alloys has been investigated. The consolidated specimens in a disc form of 10 and 26 mm in diameter and 8 mm in height were prepared by hot-pressing of rapidly solidified foils produced by a single-roller melt spinning method. Oxygen content was analyzed to be enriched in the range of 4.1 nm depth from the foil or powder surface. By the reduction-treatment process in a hydrogen atmosphere, the enriched oxygen content on the surface was decreased. For the hot-pressed specimens, the highest oxygen content was 519 ppm and the oxygen-rich area lies along the grain boundaries. As the oxygen content decreased, the carrier mobility (μ) was increased and the electrical resistivity (p) was decreased. The reduction of oxygen content by the reduction process using hydrogen gas causes the increase of μ, leading to high value of figure of merit (Z). For the specimens containing the oxygen content of 79 ppm, the maximum Z value of 3.4 x 10 -3 K -1 was obtained. There was a tendency for grain size to increase with increasing oxygen content in the hot-pressed specimens.

Amorphization in Ni-Ti-Ta system through mechanical alloying

In recent years, advances have been made in synthesizing amorphous alloys with superior properties via solid-state reactions as opposed to traditional rapid solidification techniques [1, 2] because of improved properties of the alloys produced by the former techniques. Of the many solid-state reaction techniques, mechanical alloying (MA) has proven to be a simple yet very effective technique for producing amorphous alloys. Ever since the amorphization in mechanically alloyed Ni60Nb40 powder mixture was achieved by Koch [3], the technique has been widely applied for various binary systems. However, amorphization in ternary alloys have hardly been studied [4–7]. The reason being, a lack of proper understanding of the process and variation of the products with subtle changes in the process parameters. Mechanical alloying of both Ni-Ti and Ni-Ta systems has been studied extensively [2, 8–11], but no attempt has been made on mechanical alloying of the ternary Ni-Ti-Ta system. Ta, added as a ternary element in the NiTi-alloys has been proven to impart radiopassity, thermal stability, etc. [12, 13]. Hence in this research, an attempt has been made to study the amorphous phase formation in the (Ni51Ti49)1−xTax system in the range of 0–20 at.% Ta through mechanical alloying. Pure powders (99.9%) of Ni, Ti and Ta with particle sizes less than 45 μm (-320 mesh) were mixed under inert argon atmosphere according to the formula (Ni51Ti49)1−xTax (x = 0, 2, 4, 10, 15, 20). All powder mixtures were subjected to high-energy ball milling (HEBM) in a SPEX 8000 mill. A ball to powder ratio (BPR) of 10:1 was maintained with stainless steel balls of two diameters (0.5 in. and 0.25 in.) as grinding medium. All powder mixtures were initially milled for 0.5 hr and then powders with Ta at 4 and 20 at.% were subjected to 24 hrs of milling to study the process of amorphization in the system. Microstructural analysis to assess the overall physical particle size variation and interlayer thickness of the alloyed particles with milling time was performed using a scanning electron microscope (SEM). Phase transformation during the process of amorphization was performed using a Bruker Axis transmission powder diffractometer with Mo-Kα radiation (0.71073A). In order to conduct both microstructure and phase analyses, a small amount of powdered mixture was

Critical phenomena in FINEMET alloy

The Fe 73.5Cu 1Nb 3Si 13.5B 9 FINEMET alloy has been prepared by the rapid solidification technique. The critical behaviour of this alloy in the amorphous as well as in its nanocrystalline states has been studied near their respective Curie temperatures. From the values of the critical exponents one can conclude that the alloy behaves like a 3D Heisenberg ferromagnet in the amorphous and nanocrystalline states. But there exists a slight increase in the value of β for the alloy annealed at 823 K (the nanocrystalline state) as observed in most of the amorphous alloys.