Rapid Solidification Method Research Articles

Multiscale characterization of nanostructured Al-Si-Zr alloys obtained by rapid solidification method.

Properties of engineering metallic alloys (e.g., fracture toughness, corrosion resistance) are often limited by the presence of primary intermetallic particles which form during conventional solidification. Rapid solidification brings about much more homogenous amorphous and/or nanocrystalline structure with reduced density of primary particles. Rapidly solidified thin ribbons obtained by melt spinning are usually considered as intrinsically homogenous. However, due to different cooling conditions at the wheel surface and on the side exposed to the ambient environment, structure of such ribbons may vary significantly across its thickness. The materials studied in this study were 30–40 μm thickness ribbons of nanocrystalline hyper- and hypo-eutectic Al–Si–Zr alloys produced by melt-spinning method. Transmission electron microscopy and high resolution scanning transmission electron microscopy were used to characterize the structure homogeneity across the ribbons. Thin foils for transmission observations were prepared by focused ion beam system. Microstructural observations confirmed nanocrystalline character of Al–Si–Zr alloys. However, these observations revealed inhomogeneity of the structure across the ribbon width.

Effect of High-Energy Ball Milling on Microstructure and Microwave Absorbing Properties of NdFe Material

The NdFe magnetic absorbing materials were prepared by rapid solidification and high-energy ball milling method. The effect of high-energy ball milling on particle morphology, organizational structure and microwave absorbing properties of NdFe magnetic absorbing materials were analyzed with the aid of X-ray diffractometer, scanning electron microscope and vector network analysis. The results show that the Nd2Fe17 and α-Fe phase are refined, the particles become smaller and thinner; the span-ratio of the particles increases along with time during the process of high-energy ball milling; and meanwhile, the frequency of absorbing peak reduces. The absorbing bandwidth broadens as the increase of the time of ball milling, except that of 48h.The minimum reflectance of the powder decreases from -22dB to - 44dB under the circumstances that the time of high energy ball milling reaches 48h and the thickness of the microwave absorbing coating is 1.5mm. But it rebounds to about - 6dB when the time of ball milling reaches 72h.

Solidification Behavior of Undercooled Cu<sub>98</sub>Cr<sub>2</sub> Alloys

The solidification behavior of undercooled Cu98Cr2 alloys was investigated under different rapid solidification methods. The results shown that whole lamellar (α+β) eutectics appeared in melt spun alloys for the sample undercooled into the coupled zone. The microstructure of arc melted Cu98Cr2 alloys consisted of primary β(Cr) particles distributes on α(Cu) matrix and (α+β) eutectics set in cellular α (Cu) phase. However, due to the different thickness and different solidification rate, the microstructure of splat quenched Cu98Cr2 alloys shown that only cellular supersaturated α solid solution occurred for thin flake and primary β(Cr) particles and (α+β) eutectics occurred for thicker flakes.

A Replaceable Lead-Free Solder for Sn-37Pb

In this paper, a new kind of Sn-Bi lead-free solder was fabricated via rapid solidification method by adding a series of microelements which can optimize the properties of Sn-Bi solder. When the solder was manufactured by Single Roller Melt Spinning Process, the faster the cooling rate is, the better the effect of restraining Bi segregation is. When the melt spinning rate was up to 1000 rpm, it had the best result. The effects of microelements on the melting characteristics, microstructure and properties of the new solder were also systemically studied. The results show that when the added content of Ag is 0.7%, Cu 0.3%, Ge 0.1%, In 0.5% and Sb 0.5%, the microstructure of the solder is fine, the extent of Bi segregation obviously decreases and the mechanical property is similar to that of Sn-37Pb solder. The melting point of the new solder is close to that of the Sn-37Pb solder. The mechanical and soldering properties are also similar to that of it.

Improved Thermoelectric Properties of Al-Doped Higher Manganese Silicide Prepared by a Rapid Solidification Method

Polycrystalline higher manganese silicides (HMS) Mn(AlxSi1x)1.80 (x =0 to 0.009) were prepared by a rapid melt-spinning process combined with a spark plasma sintering method (MS-SPS). The phase composition, microstructure, and thermoelectric properties of the bulk samples were investigated. X-ray diffraction (XRD) patterns showed that all samples possessed the HMS structure, but minor amounts of the MnSi phase could be observed from the backscattered electron images. When the Al content did not exceed the solid solubility limit, the electrical conductivity of Al-doped HMS increased dramatically, and the thermal conductivity decreased, as a result of the enhancement of phonon scattering due to an increased number of defects. In addition, the maximum ZT value of 0.65 was obtained at 850 K for the sample with x = 0.0015, whereas further increase in the Al content (x > 0.0015) significantly deteriorated the thermoelectric properties, mainly because the Al content exceeded its solid solubility limit in HMS.

Formation mechanism of coarse columnar γ grains in as-cast hyperperitectic carbon steels

The formation mechanism of as-cast coarse columnar γ grain (CCG) structure in hyperperitectic carbon steels is investigated by means of a rapid unidirectional solidification method. This method achieves cooling conditions similar to those in the vicinity of a practically continuously cast slab surface. The microstructural observation of the quenched samples indicates that the CCG structure develops from the mold side along the direction of the temperature gradient. In the solidifying samples, fine columnar γ grains (FCG) always exist ahead of the CCG region. Instead of continuous growth into large grains, FCG always shrink and vanish as a result of the growth of CCG initially formed near the mold side. Therefore, the grain size at a fixed point in the ingot discontinuously changes from the FCG to the CCG. The validity of this process is supported by numerical analyses. This finding is in marked contrast to the assumption made in conventional grain growth analysis on the CCG structure.

The Effect of Plastic Consolidation Parameters on the Microstructure and Mechanical Properties of Various Aluminium Powders

The present paper is aimed at investigations of mechanical properties and structure of technical purity aluminum powders prepared by plastic consolidation process. The research work is focused on effective improvement of mechanical properties of material while keeping the conductivity at high level. It is well known that application of rapid solidification method with hot extrusion technique leads to grain refinement, as so according to Hall-Petch rule, improvement in mechanical properties of material can be expected. Furthermore, additional material strength can be obtained by aluminum oxides from free surface of powders that became internal boundaries during consolidation process. Aluminum powders atomized by air, argon and water were cold compacted and extruded at temperatures of 325°C and 375°C. For comparison purposes the same extrusion conditions were applied to cast aluminum. In order to analyze effect of recrystalization process during hot extrusion operation, different extrusion temperatures were chosen. Tensile tests as well as micro-hardnes measurements showed significant increase in mechanical strength for RS samples in comparison to conventionally cast material. Structural observations by means of transmission electron microscopy revealed that grain size of materials extruded at the given temperature was at the same level, however amount and distribution of oxides particles differs significantly. It was considered that differences in strength between individual RS material were attributed to this effect.

激光快速凝固法制备织构化二钛酸钡及其介电性能研究

激光快速凝固法制备织构化二钛酸钡及其介电性能研究

Rapid synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ electrolyte by a CO 2 laser and its electric properties for intermediate temperature solid state oxide full cells

A laser rapid solidification (LRS) method has been developed for the synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ (LSGM), an excellent electrolyte for solid oxide fuel cells. It is shown that pure perovskite LSGM phase can be produced within a few seconds with this method under optimized synthetic conditions and it solidified in densely packed and relatively ordered ridge-like blocks with a relative density of 98.5%. The unique microstructures are attributed to the oriented crystalline growth in the molten pool dictated by heat transfer directions. It is found that the samples synthesized by LRS exhibit superior electrical properties for fuel cell applications to those by solid state reactions. The conductivities of 0.027, 0.079 and 0.134 S cm −1 measured at 600, 700 and 800 °C, respectively are much higher than those of the samples synthesized by solid state reactions with similar purity and density.

Effects of Cr Addition on Coarse Columnar Austenite Structure in As-Cast 0.2 mass% Carbon Steel

Effects of Cr addition on as-cast Coarse Columnar austenite Grain (CCG) structure were investigated for 0.2 mass% carbon steel by means of rapid unidirectional solidification method which realizes cooling conditions similar to those in the vicinity of continuous cast slab surface. Although the as-cast structure of the unidirectionally solidified samples always consisted of the CCGs regardless of Cr addition, the aspect ratio of the CCGs was remarkably reduced by the Cr addition. During solidification, Fine Columnar austenite Grains (FCGs) existed at the growing front of the CCG region and the migration velocity of the FCG/CCG boundary was reduced by the Cr addition. EPMA analysis revealed that the Cr addition enhances P segregation at interdendritic positions, which lowers a temperature for completion of γ transformation, Tγ. This lowered Tγ reduces the migration velocity of the FCG/CCG boundary and, as a result, induces the formation of CCGs having shorter major axis diameters.

Positron annihilation spectroscopy in nanocrystallized iron based metallic glass

AbstractSoft magnetic metallic glass of composition Fe68.5Cu1Nb3Si18.5B9 has been produced by rapid solidification method. Nanocrystallized microstructure was characterized by TEM and Positron life time spectroscopy. TEM results confirmed presence of Fe3Si and Fe2B as primary and secondary phase respectively. Two life time components were observed in amorphous and nanocrystallized samples. These components have been correlated with Microstructural features. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanostructured bulk YbxCo4Sb12 with high thermoelectric performance prepared by the rapid solidification method

High performance nanostructured bulk skutterudites YbxCo4Sb12 (x = 0.1, 0.2, 0.3) have been prepared by combining the melt spinning technique with spark plasma sintering (SPS). The effects of different linear speeds V of the spinning copper wheel on the microstructure and phase composition of ribbon samples and bulk materials are studied, and the influence of the nanostructure and Yb filling fraction on thermoelectric (TE) properties is investigated. The microstructure characterization results show that with increasing speed V, the ribbons possess finer nanostructure and a more homogeneous component distribution. As a result, the formation of the skutterudite phase during a brief SPS processing of the ribbons is very rapid. Moreover, the resulting bulk samples are single-phase, high density skutterudites with nano-scale size grains. The results of TE property measurements show that with the increasing linear speed V, i.e. with the formation of a finer nanostructure, the thermal conductivity of bulk samples decreases markedly without any significant effect on the electronic transport properties. In fact, we observe an enhancement in the Seebeck coefficient as the grain size decreases. The Yb0.3Co4Sb12 compound reaches its highest ZT of 1.22 at 800 K.

Microstructure of Rapidly Solidified Ti-46Al-2Cr-2Nb-xY Alloys

In this paper, a rapid solidification (RS) method was employed to produce yttrium-containing TiAl based alloy ribbons. The microstructure evolution was investigated in terms of yttrium addition and RS parameters. For comparison, the conventionally cast counterpart alloys were studied as well. It was found that the microstructure of as cast alloys is sensitive to the Y content. The alloys with addition of 0 to 1.0at.% Y were of lamellar microstructures, but the alloy samples with 1.5 and 2.0at.% Y additioin were of strip-like microstructure. The yttrium-free alloy exhibited full γ phase, while the Y-bearing alloys contain γ phase, a small amount of α2, and yttrium containing phases. With increasing Y content, the secondary dendritic arm spacing (SDAS) gradually reduced. In the case of the rapidly solidified alloys, the microstructure was refined evidently when compared with the as cast counterparts. The fine Y-rich precipitates were homogeneously distributed in the matrix with a particle size of several tens of nanometers. A bcc phase (a=0.314 nm) was found in the alloys containing more than 1.5at.% Y, which was attributed to the extension of the solubility of Y in the matrix by rapid solidification.

Microstructure and Grain Refining Performance of a Rapidly Solidified Al-5Ti-1B Master Alloy

A rapidly solidified Al-5Ti-1B master alloy prepared by the in-rotating-liquid spinning process has been investigated. It has been found that the in-rotating-liquid spinning process is a potential rapid solidification method to realize the continuous production of the master alloy wire on a large scale. The microstructure of the Al-5Ti-1B was evidently improved after being rapidly solidified. The agglomeration of the TiB2 particle was significantly decreased. Consequently, the grain size of the purity aluminium refined by the rapidly solidified Al-5Ti-1B was reduced by 15% compared with that refined by the master alloy prepared under normal conditions.

Synthesis and compressive deformation of rapidly solidified magnesium alloy and composites reinforced by SiC p

In this paper, rapidly solidified magnesium–aluminum (AZ91HP) alloy and magnesium alloy matrix composites reinforced by SiC p were prepared successfully by the method of rapid solidification. Microstructure of rapidly solidified AZ91HP alloy was greatly refined through the process of rapid solidification compared with as-cast AZ91HP alloy. With increasing SiC content, 0.2% YS and ultimate compressive strength of composites had been improved significantly compared with the unreinforced counterparts, accompanied by a reduction of total strain. In quasi-static compressive tests, failure in form of decohesion at the particulate–matrix interface was observed numerously as a dominant failure mode of composites. Failure of the large-sized SiC p and particulate clusters occurred widely because of the higher strain-rate and the greater load transfer from the ductile matrix to the brittle particulates in dynamic deformation.

The magnetic entropy change in CoMnSb alloys with different crystal sizes

The magnetocaloric effect (MCE) in CoMnSb has been investigated by comparing two samples with different crystal size. One sample is the ingot with crystal size of 120 nm, referred as sample A. The other with average crystal size of 30 nm has been fabricated by rapid solidification method, referred as sample B. It has been found that crystal size dramatically affects the magnetic properties and MCE for CoMnSb alloy. For example, in comparison with sample A, sample B exhibits a lower magnetization and Curie temperature, but an enhanced refrigerant capacity and broader working temperature range. These facts indicate that sample B is superior to the ingot in practical application. The above results are explained in terms of the effect of crystal size and atomic disorder on the intrinsic magnetic properties and magnetic entropy change.

Amorphous multielementary alloys: A preparation route for shape memory alloys

Rapid solidification methods (planar flow casting and twin roll casting) have been used to improve and simplify processing of shape memory alloys. Our goal is to synthesize amorphous as-cast materials and then near-net shaping can be obtained while working in the supercooled liquid temperature region. Materials are thereafter crystallized in order to recover a reversible austenite–martensite transformation. Alloying equiatomic Ni–Ti intermetallic compound with selected elements leads to better glass forming ability (GFA). Despite the fact that compositional requirements for obtaining thermoelastic reversible martensitic transformation and glass formation are different and contradictory, the pseudo-binary alloys developed by substitution of Zr, Hf for Ti, and Cu, Co, Pd, Sn for Ni are good candidates to exhibit both phenomena. We report here a choice of compositions, which after fast cooling, are amorphous and demonstrate a superplastic behaviour in the Δ T ( T x − T g) region. After an adequate thermal treatment, a martensitic phase is obtained for some compositions, and such alloys demonstrate shape memory and superelastic properties.

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.

Production and characterization of TiAl ribbons with Y additions

Rapid solidification method was employed to produce TiAl based alloy ribbons and finally to produce TiAl based alloys with novel microstructure and properties. TiAl based alloys with nominal compositions of Ti-46Al-2Cr-2Nb (atomic ratio) and various yttrium additions (0, 0.5%, 1.0%, 1.5%, 2.0%, atom fraction) were produced using the melt spinning method. For comparison, cast alloys with the same compositions were prepared by argon arc melting as well. It is shown that the as cast microstructure of Y free alloy is lamellar. With addition of Y up to 1.5%, the microstructure of the alloy changes from lamellae to dendrites, while more addition of Y leads to a finer dendrite structure. For the rapidly solidified TiAl based alloy ribbon, refined microstructure is produced. The increase of Y addition modifies the phase constituents from pure γ-TiAl phase of Y free alloy gradually to γ-TiAl+α 2-Ti 3Al and γ-TiAl+α 2-Ti 3Al+small amount of Al 2Y phase. Though the phase constituents on the two sides of ribbons, surface contacting roll and free surface, are essentially the same, the microstructure of the former one is much finer than that of the latter one.

Microstructure–magnetic properties relationships in nanocrystalline Nd–Fe–Co–Ge–B annealed ribbons

AbstractIn this work, the effects of Ge addition on the microstructure and magnetic properties of some rapidly quenched Nd13.5Fe(74.9–z )Co5.5Gez B6 alloys with z = 0.0, 0.18, 0.36, 0.54, 0.72 and 0.9 prepared by a rapid solidification method were studied. For the first time, detailed microstructural study of nanometer size grain boundaries enriched with very small amount of Ge as well as Nd was carried out using 3 Dimensional Atom Probe (3DAP) technique. The magnitudes of B r and (BH )max were seen to increase for the samples substituted with up to 0.36 at% Ge in spite of the fact that Ge is a non‐magnetic atom. This was related to the observed change of Co concenteration in matrix phase. However, the magnetic properties deteriorated for the samples with Ge addition beyond 0.36 at%. The observed magnetic properties are discussed in relation with the observed microstructural changes monitored by 3DAP and TEM techniques. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)