Rapid Solidification Method Research Articles

Structural Properties and Crystallization Behavior of FINEMET Fe74Cu1.5Nb2.5Si12B10 Alloy Under Different Annealing Condition

The effect of annealing condition on nanocrystalline amorphous FINEMET type of alloy with nominal composition Fe74Cu1.5Nb2.5Si12B10 prepared by rapid solidification method has been studied to observe the structural properties and crystallization behavior of the material. Nanocrystalline alloy with ferromagnetic bcc nanocrystals with size 15-29 nm embedded in a residual amorphous matrix was produced from amorphous precursor by appropriate annealing condition. The amorphosity of the material, primary crystallization temperature, the nanometric grain size, Si content and the lattice parameter of Fe(Si) nano-phase have been determined from XRD patterns of the samples annealed at different temperatures ranging from 475°C - 650°C with annealing time 5, 12, 20 and 30 minutes. The annealing temperature 475°C (with annealing time of 12 minutes) was determined as primary crystallization temperature with grain size 15 nm, Si content 16.25 at.% and lattice parameter 2.8431 Å. The grains were found to grow rapidly after 550°C attaining a maximum value of 29 nm at the annealing temperature of 650°C. The grain size and Si content increase whereas the lattice parameter decreases with the increase of annealing temperature and time.Dhaka Univ. J. Sci. 64(1): 71-75, 2016 (January)

Phase Formation, Thermal Stability and Mechanical Properties of a Cu-Al-Ni-Mn Shape Memory Alloy Prepared by Selective Laser Melting

Selective laser melting (SLM) is an additive manufacturing process used to produce parts with complex geometries layer by layer. This rapid solidification method allows fabricating samples in a non-equilibrium state and with refined microstructure. In this work, this method is used to fabricate 3 mm diameter rods of a Cu-based shape memory alloy. The phase formation, thermal stability and mechanical properties were investigated and correlated. Samples with a relative density higher than 92% and without cracks were obtained. A single monoclinic martensitic phase was formed with average grain size ranging between 28 to 36 μm. The samples exhibit a reverse martensitic transformation temperature around 106 ± 2 °C and a large plasticity in compression (around 15±1%) with a typical “double-yielding” behaviour.

Design and Synthesis of a Geopolymer-Enhanced Quasi-Crystalline Composite for Resisting Wear and Corrosion

Multiphase composites are attractive for improved mechanical performance and corrosion resistance. In this research, a new composite consisting quasi-crystalline Al75Mn14Si7Fe4 alloy of icosahedral, cubic α-AlMnSiFe, monoclinic Al13Fe4 phases, and ferro-silico-aluminate geopolymer was synthesized using rapid solidification and thermal treatment methods. The concentration of icosahedral phase (i-phase) was controlled and the formation of geopolymer was obtained through heat treatment. Characterization showed that the microhardness and wear resistance were increased with the amount of i-phase. The corrosion resistance, on the other hand, was improved with the existence of the geopolymer. This research demonstrates an effective approach in processing a multiphase composite that has desired properties and performance through multiphase design and composition.

Metallic glass formation at the interface of explosively welded Nb and stainless steel

The interface between explosively welded niobium and stainless steel SUS 304 was studied using scanning electron microscopy, transmission electron microscopy and energy dispersive X-Ray spectroscopy. The wavy interface along which vortex zones were located was observed. The vortex zones formed due to the mixing of materials typically had amorphous structure. Inoue’s criteria of glass formation were used to explain this result. The effect of the composition, cooling rate and pressure on the glass formation are discussed. The conditions of deformation, heating, and cooling as well as shockwaves propagation were numerically simulated. We show that the conditions of vortex zone formation resemble the conditions of rapid solidification processes. In contrast to the “classical” methods of rapid solidification of melt, the conditions of metastable phase formation during explosive welding are significantly complicated by the fluctuations of composition and pressure. Possible metastable structures formation at the interface of some common explosively joined materials is predicted.

Enhanced large magnetic entropy change and adiabatic temperature change of Ni43Mn46Sn11 alloys by a rapid solidification method

The effect of arc melting and melt-spinning on magnetocaloric effect related magnetic properties of Ni43Mn46Sn11 alloys has been contrastively studied. Different measurements based on isothermal magnetization and heat capacity were carried out. For ribbon sample, extremely high magnetic entropy change ΔSM of 41.4 J kg−1 K−1 and adiabatic temperature change ΔTad of 3.5 K (0–5 T) were achieved, which increases by 40.3% and 16.7% compared with that of bulk sample respectively. The martensitic transition related magnetic properties have been systematically discussed.

The Effect of Melt Overheating on the Melt Structure Transition and Solidified Structures of Al-La Alloy

Although the effect of overheating treatment on solidification is due to the liquid structure state, its nature and rule are still unclear. In this article, the effect of melt overheating on the melt structure transition and solidified structures of Al100−x La x alloys (x = 2, 3, 5) was mainly studied with resistivity and rapid solidification methods. The resistivity of liquid Al-La alloy increases with the temperature and La content, and it shows the linear and nonlinear changes successively. The corrosion resistance and hardness of melt-spun alloy improves with the increase in melt temperature and La content. These results indicate that the melt structure becomes homogeneous, dense, and disordered with the increase in melt temperature, and a temperature-induced liquid–liquid structure change occurs at 880–960°C. The homogeneous and dense melt structure features are remained partly in this melt-spun alloy and have a beneficial influence on its corrosion resistance and hardness. It is useful to study on the melt structure and solidified structures with the rapid solidification and resistivity method.

Process Dependence of Microstructure and Mechanical Properties for Al-Fe Based Bulk Alloys

In this work, a comparative study of the microstructure and mechanical properties of Al-8Fe based bulk alloys fabricated by three different rapid solidification methods and subsequent hot extrusion was carried out. Spray forming, gas atomization, and melt spinning methods were used as techniques for rapid solidification having various cooling rates. Equiaxed grains containing Al-Fe, Al-Fe-(Mo, V), and Al-Zr phase particles were characterized. The yield strength of the melt spun and extruded specimen was estimated to approximately 800 MPa at room temperature, a value which is roughly 1.5 times higher than that obtained for the atomized and extruded specimen and roughly 2.5 times higher than for the spray formed and extruded specimen. The higher strength of the melt spun and extruded specimen originated from a finer microstructure compared to the atomized and extruded specimen and the spray formed and extruded specimen.

Study on liquid structure feature of Al100 − xNix alloy with resistivity and rapid solidification method

In this paper, the liquid structure of Al100−xNix alloys (x=0, 2, 2.7, 5) was mainly studied with resistivity and rapid solidification method, the resistivity of liquid alloy increases with the increase of the temperature and Ni content, and shows the linear and nonlinear change successively; the various tests on melt-spun Al–Ni alloy show that the alloys, which contained amorphous structure and treated with higher melt temperature, have a favorable corrosion resistance and hardness, which can reflect and verify the liquid feature from rapidly solidified alloy and amorphous structure. These results indicate that the melt structure becomes homogeneous and disordered with rising temperature, and temperature-induced liquid–liquid structure change occurs at 850–950°C. Based on these results explored the melt structure from different aspects, we describe this melt structure and discuss shallowly the relationship between the melt and amorphous structure.

Enhanced power factor of Mg2Si0.3Sn0.7 synthesized by a non-equilibrium rapid solidification method

Sb-doped Mg 2 Si 0.3 Sn 0.7 was respectively prepared by melt spinning (MS) and by a two-step solid-state reaction (SSR), followed by plasma-activated sintering (PAS). The nonequilibrium MS technique greatly improves the structural homogeneity by rapidly quenching the homogeneous melt. As a consequence, the carrier mobility and electrical conductivity is much enhanced, leading to a record power factor of 5.18 × 10 −3 W m −1 K −2 at 600 K, a 15% improvement over the SSR–PAS sample, and a high figure of merit ZT ≈ 1.30 at 750 K.

Croatian

Shape memory alloys (SMAs) have been extensively investigated because of their unique shape memory behaviour, i.e. their ability to recover their original shape they had before deformation. Shape memory effect is related to the thermoelastic martensitic transformation. Austenite to martensite phase transformation can be obtained by mechanical (loading) and thermal methods (heating and cooling). Depending on thermomechanical conditions, SMAs demonstrate several thermomechanical phenomena, such as pseudoelasticity, superelasticity, shape memory effect (one-way and two-way) and rubber-like behaviour. Numerous alloys show shape memory effect (NiTi-based alloys, Cu-based alloys, Fe-based alloys etc.). Nitinol (NiTi) is the most popular and the most commonly used SMA due to its superior thermomechanical and thermoelectrical properties. NiTi alloys have greater shape memory strain and excellent corrosion resistance compared to Cu – based alloys. However, they are very costly. On the other hand, copper-based alloys (CuZn and CuAl based alloys) are much less expensive, easier to manufacture and have a wider range of potential transformation temperatures. The characteristic transformation temperatures of martensitic transformation of CuAlNi alloys can lie between −200 and 200 °C, and these temperatures depend on Al and Ni content. Among the Cu – based SMAs, the most frequently applied are CuZnAl and CuAlNi alloys. Although CuZnAl alloys with better mechanical properties are the most popular among the Cu-based SMAs, they lack sufficient thermal stability, while CuAlNi shape memory alloys, in spite of their better thermal stability, have found only limited applications due to insufficient formability owing to the brittle γ2 precipitates. The most important disadvantage of polycrystalline CuAlNi alloys is a small reversible deformation (one-way shape memory effect: up to 4 %; two-way shape memory effect: only approximately 1.5 %) due to intergranular breakdown at low stress levels. The technologies for production of shape memory alloys are induction melting, vacuum melting, vacuum arc melting, following hot and cold working (forging, rolling, wire drawing). In addition, rapid solidification methods, like melt spinning and continuous casting have been developed. These methods are characterized by high cooling rates. High cooling rates allow very short time for diffusion processes and may lead to extremely fine microstructure, better homogeneity etc. SMAs have found applications in many areas due to their thermomechanical and thermoelectrical properties (biomedical applications, engineering industry, electrical industry). In this paper, a review of shape memory alloys, properties and applications of mentioned materials is presented.

The Production of Material with Ultrafine Grain Structure in Al-Zn Alloy in the Process of Rapid Solidification

Abstract In the aluminium alloy family, Al-Zn materials with non-standard chemical composition containing Mg and Cu are a new group of alloys, mainly owing to their high strength properties. Proper choice of alloying elements, and of the method of molten metal treatment and casting enable further shaping of the properties. One of the modern methods to produce materials with submicron structure is a method of Rapid Solidification. The ribbon cast in a melt spinning device is an intermediate product for further plastic working. Using the technique of Rapid Solidification it is not possible to directly produce a solid structural material of the required shape and length. Therefore, the ribbon of an ultrafine grain or nanometric structure must be subjected to the operations of fragmentation, compaction, consolidation and hot extrusion. In this article the authors focussed their attention on the technological aspect of the above mentioned process and described successive stages of the fabrication of an AlZn9Mg2.5Cu1.8 alloy of ultrafine grain structure designated for further plastic working, which enables making extruded rods or elements shaped by the die forging technology. Studies described in the article were performed under variable parameters determined experimentally in the course of the alloy manufacturing process, including casting by RS and subsequent fragmentation.

NUMERICAL SIMULATION OF DENDRITE GRAIN GROWTH OF DD6 SUPERALLOY DURING DIRECTIONAL SOLIDIFICATION PROCESS

Modern aero and power industry needs high- performance gas turbine. Directional solidification(DS) columnar grain and single crystal(SX) blade as key parts of gas turbine serve in heavy stress and high temperature conditions. The DS and SX blade are mainly produced by high rapid solidification(HRS) method, and HRS is one of useful DS technology, which has a property that the heat dissipating ways are changing during the process and the temperature gradients will vary correspondingly. The dendrite grain arrays were the substructure of a DS or SX blade. The structure of the dendrite grain arrays influences the mechanical property of the final casting very much, but is seriously affected by the solidification parameters, such as temperature gradient. In this work, the dendrite grain growth of DD6 superalloy was studied based on cellular automaton-finite difference(CA- FD) model concerning the HRS method's macro solidification parameters. Mathematic models for dendrite grain growth controlled by temperature field and solute field were built to describe the competitive growth and morphology evolution of dendrite grains. Then the dendrite calculation model was coupled with the models of DS process calculation, and some HRS solidification parameters were included, such as withdrawal rate, pouring temperature, etc. The coupled models were used to predict the dendrite grain competitive growth of DD6 superalloy during the DS process. The variation of solute distribution and the dynamic adjustment of dendritic spacing during the process could be predicted by simulating calculation. The DS experiment was carried out with a cylinder sample, and dendrite grains' distribution in the transverse and longitude section was observed by OM and SEM. Then the simulated dendritic morphology was compared with that by experiment. The primary and secondary dendritic spacing by experiment and simulation were measured, and the compared results revealed that as the DS process going on the temperature gradient decreased gradually and the primary dendritic spacing was increasing. So simulation results of the DS dendritic competitive growth were validated by the experiment results, and the proposed models could predict the dendrite grain morphology and the adjustments of DS dendritic spacing of DD6 superalloy very well.

Synthesis of high strength aluminum alloys in the Al–Ni–La system

Abstract

Effect of Magnesium Addition and Rapid Solidification Procedure on Structure and Mechanical Properties of Al-Co Alloy

Tested Al-5Co and Al-5Mg-5Co materials were manufactured using a common ingot metallurgy (IM) and rapid solidification (RS) methods combined with mechanical consolidation of RS-powders and hot extrusion procedures. Mechanical properties of as-extruded IM and RS alloys were tested by compression at temperature range 293-773 K. Received true stress vs. true strain curves were typical for aluminum alloys that undergo dynamic recovery at high deformation temperature. It was found that the maximum flow stress value for Al-5Mg-5Co alloy was much higher than that for Al-5Co, both for IM and RS materials tested at low and intermediate deformation temperatures. The last effect results from the solid solution strengthening due to magnesium addition. However, the addition of 5% Mg results also in the reduction of melting temperature. Therefore, the flow stress for Al-5Mg-5Co alloy was relatively low at high deformation temperatures. Light microscopy observations revealed highly refined structure of RS materials. Analytical transmission electron microscopy analyses confirmed Al9Co2 particles development for all tested samples. Fine acicular particles in RS materials, ∽1μm in size, were found to grow during annealing at 823K for 168h. As result, the hardness of RS materials was reduced. It was found that severe plastic deformation due to extrusion and additional compression did not result in the fracture of fine particles in RS materials. On the other hand, large particles observed in IM materials (∽20μm) were not practically coarsened during annealing and related hardness of annealed samples remained practically unchanged. However, processing of IM materials was found to promote the fracture of coarse particles that is not acceptable at industrial processing technologies.

Enhanced wear resistance in Zr-based bulk metallic glasses by hydrogen

Plate-like Zr60Ni25Al15 bulk metallic glasses (BMGs) were prepared under the gaseous mixture of hydrogen and argon. The effects of hydrogen on micro-hardness and wear resistance of the BMGs were researched. The results showed that BMGs fabricated under the gaseous mixture of hydrogen and argon exhibit higher micro-hardness and superior wear resistance, i.e., hydrogen addition can increase the wear resistance of bulk metallic glass dramatically. The enhanced wear resistance of the BMGs is attributed to the increment in micro-hardness and free volume introduced by the addition of hydrogen into the BMG matrix. The findings in present paper demonstrate that rapid solidification methods combining with hydrogenation could be an attractive means to improve the mechanical properties of bulk metallic gasses.

Magnetic properties of Nd-Fe-Co-Al rapid solidification alloys

Abstract Nd-Fe–Al–Co alloys with thickness of 0.05–4 mm were prepared by means of rapid solidification methods, suction-casting and melt-spinning, and investigated using X-ray diffraction, electron microscopy and magnetization measurements. With appropriate composition and quenching rate, the alloys behave as single-phase hard magnetic materials. Coercivity of the alloys can reach 7.6 kOe at room temperature and exceed 30 kOe at 100 K. When the thickness of the alloys is increased, multi-magnetic phase behavior is clearly performed and Nd2Fe15Al, NdAl2, Nd3Al and Nd phases are further crystallized. The optimal hard magnetic properties of the alloys closely related to a microstructure which consists of nanocrystallites with size of 10–30 nm dispersed in an amorphous matrix. The hard magnetic phase in the alloys belongs to the amorphous phase. The nanocrystallites, whose total volume fraction is very small in comparison with that of the amorphous phase, probably act as pinning centers, resulting in high coercivity behavior of the alloys.

Enhanced electrical conductivity of La2Mo1.4W0.6O9 ceramic prepared by laser rapid solidification method

A new method, laser rapid solidification, has been employed to prepare a kind of oxygen ion conductor—La2Mo1.4W0.6O9 ceramic. XRD and TGA measurements demonstrate that this material is of β-La2Mo2O9 structure from room temperature to 800 °C. Images from scanning electron microscopy reveal that the sample is composed of relatively oriented large blocks paralleling to the laser incident beam and its microstructure is totally different from those of conventionally sintered ceramic. Results of AC impedance spectroscopy indicate that the influence of grain boundaries is little in the crystal solidification direction and the samples exhibit high electrical conductivity. For example, the values are 2.2 × 10−3 S cm−1, 0.017 S cm−1, 0.058 S cm−1 and 0.09 S cm−1 in dry air at 500 °C, 600 °C, 700 °C and 800 °C, respectively, which are about three to five times as high as those of samples prepared by solid state reaction method. It is suggested from the brick layer model that the main reason for the increase is the less grain boundary effect associated with the special microstructure of the samples.

Influence of Heat Treatment on Magnetic Properties of Nanocrystalline Nd9Fe84Zr1B6 Ribbons Received by Rapid Solidification Method

Influence of Heat Treatment on Magnetic Properties of Nanocrystalline Nd9Fe84Zr1B6Ribbons Received by Rapid Solidification MethodThe effect of the annealing on the phase composition and magnetic properties of nanocomposite melt-spun Nd9Fe84Zr1B6ribbons has been investigated. From the X-ray diffraction studies confirmed be thermomagnetic curves measurements results that the microstructure of the material investigated is composed of a mixture of magnetically hard Nd2Fe14B and soft α-Fe, Fe3B nanosized grains. The small amount of undesirable Nd2Fe23B3metastable phase has been found which do not decompose at the highest annealing temperature. The hysteresis loop measurements certify that the ribbon annealed at 863K show the best coupling between the hard and soft magnetic phases and thus the highest coercivity of 0.38T. The grain sizes increase with increasing annealing temperature causing the coercivity to be decrease.

Mechanism of unique hardening of dental Ag–Pd–Au–Cu alloys in relation with constitutional phases

The objective of this research was to investigate the effect of constitutional phases on the unique hardening behavior of as-solutionized dental Ag–Pd–Au–Cu alloy fabricated by cold rolling. The commercial dental Ag–Pd–Au–Cu alloy fabricated by cold rolling consists of Cu-rich α1, Ag-rich α2, and β phases. On the other hand, the Ag–Pd–Au–Cu alloy fabricated by the liquid rapid solidification (LRS) method consists of single α phase. They were subjected to various heat treatments, respectively. The microstructures were observed by scanning electron microscope, transmission electron microscope and X-ray diffraction. The hardness was evaluated by a Vickers micro-hardness tester. In the Ag–Pd–Au–Cu alloy fabricated by cold rolling, the fine L10-type-ordered β′ phase is precipitated and the coarse β phase is remained after solution treatment at 1123K. The hardness increases drastically. On the other hand, in the Ag–Pd–Au–Cu alloy fabricated by LRS method, the single α phase was decomposed into the α1 phase and the α2 phase after solution treatment at 1023K and its hardness change was small. However, after aging treatment at 673K, the fine β phase is precipitated in the α phase and the hardness increases greatly even in the Ag–Pd–Au–Cu alloy fabricated by LRS method. It is considered that the precipitation of the fine L10-type-ordered β′ phase may contribute strongly to the unique hardening in the as-solutionized dental Ag–Pd–Au–Cu alloy fabricated by cold rolling.

Textured BaTi2O5 ceramic synthesized by laser rapid solidification method and its dielectric properties

Textured poly crystalline barium dititanate BaTi2O5 (BT2) ceramics with a preferred 〈010〉 orientation were synthesized by laser rapid solidification method, with a CO2 laser. The 〈010〉 orientation of the BT2 is along the laser incident direction, and the orientation factor (f) and relative density of the unannealed BT2 sample are 0.40 and 96.2%, respectively. The two quantities increase with increasing annealing time, and reach the maximum values of 0.42 (annealed at 1,000 °C for 12 h) and 97.5% (annealed at 1,000 °C for 24 h), respectively. The images of scanning electron microscopy reveal that the BT2 are composed of flake-like microstructures with the maximum thickness of 20 μm and dimension of 0.6 mm, which are parallel to the laser incident direction. The measured Curie temperature (T c) and the maximum dielectric constant (emax) are 443 and 6,000 °C, respectively.