Spray Casting Research Articles

가스분무주조 Cu-Sn-Ni-Si 합금의 미세조직 및 상온 인장성질

In this study, Cu-10Sn and Cu-10Sn-2Ni-0.2Si alloys have been manufactured by spray casting in order to achieve a fine scale microstructure and high tensile strength, and investigated in terms of microstructural evolution, aging characteristics and tensile properties. Spray cast alloys had a much lower microhardness than continuous cast billet because of an improved homogenization and an extended Sn solid solubility. Spray cast Cu-Sn-Ni-Si alloy was characterized by an equiaxed grain microstructure with a small-sized (Ni, Si)-rich precipitates. Cold rolling of Cu-Sn-Ni-Si alloy increased a tensile strength to 1220 MPa, but subsequent ageing treatment reduced a ultimate tensile strength to 780 MPa with an elongation of 18%.

분무주조에 의해 제조된 Cu-Sn계 합금의 미세조직 및 인장성질

Cu-Sn based alloys were manufactured by gas atomization spray casting route in order to achieve a fine scale microstructure and a high tensile strength. The spray cast Cu-10Sn-2Ni-0.2Si alloy had an equiaxed grain microstructure, with no formation of brittle <TEX>${\delta}-Cu_{41}Sn_{11}$</TEX> phase. Aging treatment promoted the precipitation of finely distributed particles corresponding to <TEX>${\delta}-Ni_2Si$</TEX> intermetallic phase throughout the <TEX>$\alpha$</TEX>-(CuSn) matrix. The cold-rolled Cu-Sn-Ni-Si alloy had a very high tensile strength of 1200 MPa and an elongation of 5%. Subsequent aging treatment at <TEX>$450^{\circ}C$</TEX> for 1h slightly reduced the tensile strength to 700 MPa and remarkably increased the elongation up to 30%. This result has been explained by coarsening the precipitates due to over aging and reducing the dislocation density due to annealing effects.

Effects of Composition, Orientation and Temperature on the O2 Permeability of Model Polymer/Clay Nanocomposites

Studies of the barrier properties of polymer/layered silicate nanocomposites have traditionally focused on systems with low organoclay contents, with very little work comparing theory and experiment over broad composition ranges. As a result, in spite of many reports of promising enhancements in barrier properties, the envelope of applicability nanocomposite barrier models is generally unknown, making predictive modeling and materials design difficult if not impossible. In this work, model polystyrene (PS)/dimethyl ditallow modified montmorillonite (DMDT-MMT) nanocomposites are produced via a novel spray casting technique capable of creating homogeneous, free-standing nanocomposite films. This approach provides a single experimental methodology for producing films of pure polymer, pure organoclay, or any intermediate composition, with consistently high levels of layer orientation in all cases. The results of oxygen permeation analysis (OPA) performed on these model materials (0−100 vol % organoclay in 10% increments) are compared to the results from all models commonly used for nanocomposite barrier properties modeling, both before and after the addition of a correction factor for actual layer orientation as measured by 2D wide-angle X-ray diffraction (WAXD), and with fitting parameters limited to physically meaningful values. We report substantial improvements in barrier properties in spite of the absence of exfoliation, with the model fits implying that the permeating species remain sensitive to the aspect ratio of individual platelets at all organoclay contents. While all models match our experimental data at low organoclay contents, significant differentiation occurs as organoclay content is increased. Finally, we confirm that the permeability of these materials follows an Arrhenius relation vs temperature, albeit scaled to lower values as a function of inorganic content.

Navigating the Color Palette of Solution-Processable Electrochromic Polymers

Solution-processable electrochromic (EC) polymers that can be switched from one distinct color state to a highly transmissive and near colorless state are required for applications in both EC windows and displays. Using a tour around the color wheel, we describe the various EC polymer (ECP) compositions that now make a full palette of colors available demonstrating a set of structure−property relationships. Electrochemical and electrochromic characterization methodologies are described and their application to ECPs demonstrated. Processing and patterning methods including spray casting, screen-, flexo-, and ink jet printing, along with photo- and soft lithography are described. Absorptive/transmissive (window type) and absorptive/reflective (display type) devices are described as platforms for practical applications.

Conformal ZnO nanocomposite coatings on micro-patterned surfaces for superhydrophobicity

A conformal coating process is presented to transform surfaces with inherent micro-morphology into superhydrophobic surfaces with hierarchical surface structure using wet chemical spray casting. Nanocomposite coatings composed of zinc oxide nanoparticles and organosilane quaternary nitrogen compound are dispersed in solution for application. The coating is applied to a micro-patterned polydimethylsiloxane substrate with a regular array of cylindrical microposts as well as a surface with random micro-structure for the purpose of demonstrating improved non-wettability and a superhydrophobic state for water droplets. Coating surface morphology is investigated with an environmental scanning electron microscope and surface wettability performance is characterized by static and dynamic contact angle measurements.

Fabrication of stable, transparent and superhydrophobic nanocomposite films with polystyrene functionalized carbon nanotubes

Stable, transparent and superhydrophobic carbon nanotube (CNT) nanocomposite films were fabricated by one-step spray casting process using the polystyrene functionalized CNTs, which were prepared by “living” free-radical polymerization and analyzed by means of infrared spectroscopy and thermal gravimetric analysis. The CNT film has a high water contact angle of 160° and a sliding angle of less than 3°. The surface topography of the fabricated film was characterized by field emission scanning electron microscopy. The transparency of the CNT film was investigated by UV–vis spectroscopy. The result shows that the CNT film has light transmittance of about 78% in the visible light region.

Solidification microstructures of Al-Zn-Mg-Cu alloys prepared by spray deposition and conventional casting methods

High strength Al-Zn-Mg-Cu alloys were prepared by spray deposition and casting techniques. The microstructures of the Al-Zn-Mg-Cu alloys were studied using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Secondary phases in the microstructures of the alloys prepared by spray deposition and conventional cast were examined. The results indicate that under the conventional casting condition, the microstructure of the alloy revealed the presence of coarse Al/Mg(ZnCu) 2 eutectic phases, and the spray deposited process causes an obvious modification in size, morphology, and distribution of secondary phases in the microstructure as well as reduction of segregation. The superior microstructure of the spray-deposited Al-Zn-Mg-Cu alloy was attributed to the high cooling rate, and associated with the rapid solidification process.

Defunctionalization of Ester-Substituted Electrochromic Dioxythiophene Polymers

This work demonstrates a simple process to form insoluble poly(3,4-propylenedioxythiophene) (Poly[ProDOT]) films by defunctionalization of a soluble form, which is useful in the fabrication of multilayer polymer devices. Three new ester disubstituted Poly[ProDOTs], soluble in common organic solvents, including chloroform, methylene chloride, toluene, tetrahydrofuran, and ethyl acetate, have been synthesized by oxidative polymerization using iron(III) chloride. These Poly[ProDOT-diesters] have the expected repeat unit stuctures along with GPC determined number-average molecular weights ranging from 9000 to 12 000 g mol-1. Dilute polymer solutions in toluene exhibited red fluorescence with quantum efficiencies from 0.24 to 0.32. Homogeneous thin films were formed by spray casting polymer solutions onto ITO coated glass slides and compared to films prepared by electropolymerization. These Poly[ProDOT-diesters] are electroactive, switching from a dark blue-purple to a transmissive sky blue when potentials are applied between −0.9 and +0.3 V vs Fc/Fc.+ A thin film saponification method was developed and rendered the spray-cast films insoluble by submersion into 0.1 M KOH in hot methanol for 1 h to remove the solubilizing ester group. In the case of a bis(heptanoate) Poly[ProDOT-diester] (1), spectroelectrochemistry showed minimal change in its electronic spectra after methanolysis and the resulting alcohol-substituted polymer (Poly[ProDOT-diol] (4)) could be repeatably switched between neutral and oxidized states in subsecond times. In contrast, when a more highly functionalized Poly[ProDOT-tetraester] (3) was used, a small change in the electronic spectrum which is associated with a distinct color change from burgundy to blue was observed upon methanolysis to Poly[ProDOT-tetraol] (6). The insoluble alcohol-substituted polymer films were found to be efficient hole transport layers in polymer light-emitting diodes.

An Investigation of Cavitation in the Tensile Testing of a Spray-Cast Aluminum Alloy Processed by ECAP

A commercial aluminum 7034 alloy, produced by spray casting and having an initial grain size of ~2.1 μm, was subjected to equal-channel angular pressing (ECAP) through six passes at 473 K. In the as-pressed condition, the microstructure was reasonably homogeneous and the grain size was reduced to an ultrafine grain size of ~0.3 μm. This alloy contains MgZn2 and Al3Zr precipitates which restrict grain growth. In tensile testing at 673 K after processing by ECAP, an elongation of &gt;1000% was achieved at a strain rate of 1.0 × 10-2 s-1 corresponding to high strain rate superplasticity. Quantitative cavity measurements were conducted on the specimens after tensile testing for both the as-received condition and after ECAP. These measurements reveal a significant number of small cavities in the samples and especially in the sample that exhibited a very high elongation. This paper describes the morphology of cavity development in the spray-cast aluminum alloy in both the as-received and as-pressed condition.

분무 주조 과공정 Al-Si 계 합금의 응력이완 및 Creep 천이 거동

Hypereutectic Al-Si alloys have been regarded attractive for automotive and aerospace application, due to high specific strength, good wear resistance, high thermal stability, low thermal expansion coefficient and good creep resistance. Spray casting of hypereutectic Al-Si alloy has been reported to provide distinct advantages over ingot metallurgy (IM) or rapid solidification/powder metallurgy (RS/PM) process in terms of microstructure refinement. In this study, hypereutectic Al-25Si-2.0Cu-1.0Mg alloy was prepared by OSPREY spray casting process. The change of strain rate sensitivity and Creep transition were analyzed by using the load relaxation test and constant creep test. High temperature deformation behavior of the hypereutectic Al-Si alloy has been investigated by applying the internal variable theory proposed by Chang et al. Especially, the creep resistance of spray casted hypereutectic Al-Si alloy can be enhanced considerably by the accumulation of prestrain.

Spray Coatable Electrochromic Dioxythiophene Polymers with High Coloration Efficiencies

Four new disubstituted propylenedioxythiophene polymers have been synthesized by Grignard metathesis on the 1−5 g scale. All polymers were found to be soluble in chloroform, methylene chloride, toluene, and tetrahydrofuran and were fully structurally characterized having GPC determined number-average molecular weights ranging from 33000 to 47000 g mol-1. Dilute polymer solutions in toluene exhibited strong red fluorescence with moderate quantum efficiencies from 0.38 to 0.50. Homogeneous thin films were formed by electropolymerization and spray casting polymer solutions onto ITO coated glass slides at thicknesses of ca. 150 nm. The films were electroactive, switching from a dark blue-purple to a transmissive sky blue upon p-doping, often with subsecond switching times, and high electrochromic contrast luminance changes (% ΔY) of 40−70%. These studies revealed that the branched derivatives, [poly(3,3-bis(2-ethylhexyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)] and [poly(6,8-dibromo-3,3-bis(2-ethylhexyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)], gave an electrochemical response and associated color change over a much smaller voltage range in comparison to the linear chain substituted derivatives, [poly(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)] and [poly(3,3-bis(octadecyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)]. Composite coloration efficiency values were found up to 1365 cm2/C; this was considerably larger than values obtained from previously studied alkylenedioxythiophene based polymers (∼375 cm2/C).

Using ECAP to achieve grain refinement, precipitate fragmentation and high strain rate superplasticity in a spray-cast aluminum alloy

An aluminum 7034 alloy, produced by spray casting and with an initial grain size of ~2.1 μm, was processed by equal-channel angular pressing (ECAP) at 473 K to produce an ultrafine grain size of ~0.3 μm. It is shown that the rod-like MgZn 2 precipitates present in the as-received alloy are broken into very small spherical particles during ECAP and these particles become distributed reasonably uniformly throughout the material. The presence of these fine MgZn 2 particles, combined with a distribution of fine Al 3Zr precipitates, is very effective in restricting grain growth so that submicrometer grains are retained at elevated temperatures up to at least ~670 K. Tensile testing of the pressed material revealed high elongations to failure, including elongations of >1000% when testing at a temperature of 673 K at initial strain rates at and above 10 −2 s −1. These results confirm the occurrence of high strain rate superplasticity in the spray-cast alloy.

Spray casting of eutectic ferrous alloys, an alternative to powder metallurgy

The technique of atomising liquid metal and compacting the spray to the deposit on a moving substrate combines advantages from cast, wrought and powder metallurgical materials. A production rate of several tons per hour requires precisely controlled processing. Parameters based on physical, metallurgical and technological knowledge have been determined by fundamental investigations in a special research program (SFB 372) of DFG (Deutsche Forschungsgemeinschaft). Because of the advantage of near net shape production as due to casting, this process avoids partially machining which leads to a reduction in production costs. Research on high carbon steel and cast alloys was done to study the applicability of this low cost spray cast technology instead of expensive powder metallurgy production.

The toroidal field coil design for ARIES-ST

An evolutionary process was used to develop the toroidal field (TF) coil design for the ARIES-spherical torus (ST). Design considerations included fabricability, assembly, maintenance, energy efficiency, and structural robustness. Design options were identified early in the process. Trade studies were carried out to identify preferred choices. Design points were re-optimized based on the design choices in the TF and other systems. An attractive design for the ARIES-ST TF coil system evolved. This design addresses a number of the concerns (complexity) and criticisms (high cost, high recirculating power) of fusion. It does this by: applying advanced, but available laser forming and spray casting techniques for manufacturing the TF coil system; adopting a simple single turn TF coil system to make assembly and maintenance much easier. The single turn design avoids the necessity of using the insulation as a structural component of the TF coils, and hence, is much more robust than multi-turn designs; using a high conductivity copper alloy and modest current densities to keep the recirculating power modest.

Fabrication of spray-formed hypereutectic Al–25Si alloy and its deformation behavior

This article reports the fabrication of hypereutectic Al–25Si alloy, which is expected to be applied to the cylinder liner part of the engine block of an automobile due to its excellent wear resistance, low density and low thermal expansion coefficient, through a spray casting process and the characterization of the microstructural and the mechanical properties of this alloy. The OSPREY process used in this study is one of spray forming techniques, which can produce semi-finished products such as billet, tube, and plate with rapid solidification (RS) structure and density in a single operation from molten metal. The obtained microstructure of the hypereutectic Al–25Si alloy appeared to consist of Al matrix and equiaxed Si particles with average diameter of 5–7 μm. To characterize the deformation behavior of this alloy, a series of load relaxation and compression tests have been conducted at temperatures ranging from RT to 500 °C. The strain rate sensitivity parameter ( m) of this alloy has been found to be very low (≤0.1) below 300 °C and reached maximum value of about 0.2 at 500 °C. During the deformation above 300 °C in compression, remarkable strain softening has been observed. The extrusion has been successfully conducted at the temperatures of 300 °C and above with the ratio of area reduction of 28 and 40 in this study.

Studies on spray casting of Al-alloys and their composites

A spray nozzle of convergent–divergent configuration was used for spray castings (SC) of A16061/LM25 alloys and their composites. Both monolithic alloys and composites showed equiaxed fine grained microstructure with a variation in grain size from 20 to 30 μm. Some of the regions of the preform also showed cellular solidification structure with globularization of most of the eutectic Si suggesting the effect of rapid solidification. High defect concentration in both SC matrix and their composites was observed with bulk SC samples showing uniformly distributed porosity. TEM studies showed decoration of grain boundaries/presolidified droplets by some precipitates and also vacancy loops. Their aging characteristics indicated lowering of solutionising temperature and aging time to get the same peak hardness as obtained in the alloy produced by ingot metallurgy methods. An ordered phase with unit cell four times larger than Al seems to form during the in situ heating of LM25–SiCp samples while dislocations seem to emerge from the interface between the particle and the matrix. The results are discussed in the light of reported literature on spray casting/melt spinning of Al-alloys and composites.

A comparative characterization of near-equiaxed microstructures as produced by spray casting, magnetohydrodynamic casting and the stress induced, melt activated process

The near-equiaxed microstructure of wrought and cast aluminum alloys as produced by the most common methods used to provide material for subsequent semisolid processing, is examined. More specifically, the grain size and degree of spheroidization of alloys produced by spray casting, magnetohydrodynamic (MHD) casting and the stress induced, melt activated (SIMA) process are characterized and compared. It is shown that the microstructure of alloys with the same composition differs significantly when produced by the three methods, showing the influence of the production method. Spray casting and the SIMA process result in a microstructure with perfectly equiaxed grains that is inherently suitable for semisolid processing, while MHD-cast alloys exhibit a non-uniform initial microstructure, with dendritic features dominant at the perimeter of the casting. Finally, the mechanisms responsible for the formation of near-equiaxed microstructure for each method are investigated.

Evolution of near-equiaxed microstructure in the semisolid state

The microstructure of alloys with a near-equiaxed microstructure, produced by spray casting, magnetohydrodynamic (MHD) casting and the stress induced, melt activated (SIMA) process, as it evolves within short times in the semisolid state, is examined by rapid quenching and isothermal soaking experiments. Quenching experiments reveal the morphology and distribution of solid phase at high and medium volume fractions of liquid. At medium liquid content, the microstructure of spray-cast and SIMA alloys consists of discrete equiaxed grains uniformly dispersed in the liquid phase, while the corresponding microstructure of MHD-cast alloys exhibits extensive agglomerates consisting of incompletely spheroidized grains. The connectivity of solid phase and the formation of a solid skeleton in the semisolid state are discussed in terms of grain misorientation. Isothermal soaking experiments investigated grain growth and degree of spheroidization as a function of soaking time and liquid content in the semisolid state. Results demonstrated that MHD-cast microstructures are less equiaxed compared with SIMA and spray-cast alloys even after 5 min of soaking in the semisolid state. It is also shown that the grain growth rate is smaller in spray-cast alloys than in SIMA alloys. The role of coalescence and the effects of alloying elements are also discussed.

Ultrafine grain structures formed by thermomechanical processing of spray cast Al–Li alloys

Spray casting has been used to produce Al–Li alloys with an initial grain size of about 10–20 μm and higher levels of dispersoid forming elements (zirconium, titanium, scandium) than can be achieved by conventional casting. Materials with a range of dispersoid densities have been investigated. On thermomechanical processing at elevated temperatures, it has been found that the high volume fraction of fine dispersoids prevents discontinuous recrystallisation mechanisms operating. However, on deformation to high strains, the deformed fibrous grains become unstable and can be induced to break up into a highly desirable microstructure of very fine equiaxed grains with a size of 1–2 μm. The intensity of the rolling texture has also been found to reduce greatly with finer dispersoid interparticle spacings, leading to materials with high strengths, an ultrafine equiaxed grain structure, and low anisotropy in the sheet form.

Cast microstructure and dispersoid formation in spray deposited Al–Li alloys

Spray deposition has been used to increase the concentration of dispersoid forming elements in model Al–Li–TM alloys (where TM stands for transition metals). The cast grain structure and the composition and stability of the dispersoids formed after a range of precipitation treatments was investigated. Very fine, nearly uniform, grain structures were obtained in the sprayed billets. The smallest grain size produced was 13 μm. The substantial grain refinement achievable by spray casting is partly owing to the high cooling rates, but was also found to be strongly dependent on the content and combination of the peritectic dispersoid forming elements, which increase the survival of dendrite fragments formed on impact of the semisolid metal droplets. It was found that materials with the highest peritectic forming element concentrations showed the finest grain size. Combinations of Zr and Ti gave the best grain refinement. The influence of Ti, V, and Sc on the composition and coarsening rates of the β′ Al3 (Zr,X) L12 dispersoids formed during post-spraying precipitation treatments was also investigated. The elements Ti and Sc were found to be soluble in the Al3 (Zr,X) L12 phase substituting for Zr in proportion to the average alloy composition. Titanium containing Al3 (Zr,X) L12 β′ phase dispersoids had the slowest coarsening rates, but their stability was reduced by the presence of Ti and they transformed to the equilibrium D023 phase after prolonged heat treatment. On aging, the precipitation behaviour of the δ′ phase was also affected by the Ti additions.