Papers by Keyword: Eutectic

Abstract: The eutectic structure in Mg-6Gd-3.7Nd based alloy was characterized to be result of a 'quasibinary eutectic reaction' L→ α-Mg + β-Mg₅RE. The ST temperature applied was apparently sufficient to melt the GB regions of the as-cast Mg-Gd-Nd based alloy, and transform the eutectic structures to a globular liquid phase enriched with RE elements. High supersaturation of Mg matrix by rare earth (RE) elements after quenching of solution treated Mg-Gd-Nd alloy provides sequential precipitation of different metastable phases: α-Mg (S.S.S.S.) → β'' (Mg₃RE, DO₁₉)→ β' (Mg₇RE, BCO) → β₁ (Mg₃RE, FCC) → β (Mg₅RE, FCC). The stable β precipitates grew from the eutectic structure in the form of needle-like precipitates. These needles seem to be a continuation of the β phase presented in the eutectic structure. These β precipitates grow at the expense of smaller β₁ and β precipitates presented in the α-Mg matrix. The combination of HRTEM, TEM with SAED and JEMS simulation was carried out to characterize the nanometer-scale precipitates. Microhardness measurements were performed to reveal the effect of precipitation on the mechanical properties of the alloys.

Abstract: Solidification behaviors of hypoeutectic Ni-3.3wt% B and hypereutectic Ni-4.5wt% B alloys were investigated by using differential scanning calorimetry (DSC) technology. Experimental results showed that the solidification behaviors are similar for the two kinds of alloys with small sizes, i.e. three transformed peaks (corresponding to L→α-Ni, L→Ni-Ni₂₃B₆ and Ni₂₃B₆→Ni+Ni₃B, respectively) appear in the cooling curves, and three phases (primary phase α-Ni, rod eutectic and dot precipitates) appear in the microstructures, which are different from that of the alloys with large sizes. It can be attributed to the fact that the nucleation of α-Ni and Ni₂₃B₆ phases are easier than that of Ni₃B phase for small samples of hypoeutectic and hypereutectic Ni-Ni₃B alloys.

Abstract: The possibilities of forming submicroporous and nanoporous structures in metallic materials by laser thermocycling as eutecticis reached were determined. With the implementation of the selected modes of laser treatment on L62 brass samples with a thickness of 50 µm leads to the formation of wrinkled relief, which indicates an increment of alloy volume in this area, that is, a porosity increment in the metallic material. Submicroporous and nanoporous structures are formed in the copper-zinc L62 alloy sample, which appear on the surface of the sample. Nanopores have a shape similar to equiaxial. Submicropores are formed as a result of nanopores merger. A relief is formed on the surface consisting of depressions having a shape similar to that of a hemisphere and a linear structure, oriented along the direction of rolling process.

Abstract: Menthol was used as sublimate eutectic compound to prepare the volatile eutectic solvent by mixing with camphor, borneol or N-Ethyl-5-methyl-2-(1-methylethyl) cyclohexanecarboxamide (WS-3). The system of menthol:camphor, menthol:borneol and menthol:WS-3 in various ratio (1:9 to 9:1) was characterized. The 5:5 menthol:camphor system showed the highest evaporation rate. Ibuprofen dissolved in eutectic solvent was used as internal phase of emulsion whereas tween80 was used as emulsifier. Eutectic solvent was evaporated to induce the transformation of emulsion droplet to small particle. Eutectic could be used as solvent for preparing small size suspension (14.81±0.44 µm) without organic solvent used.

Abstract: Authors have studied the interaction between high-melting compounds from various classes, such as transition-metal carbides, borides, nitrides, and silicides, and covalent-bonded B₄C, SiC, Si₃N₄, AlN etc. (over 160 phase diagrams), ternary B₄C-SiC-Me^dB₂, SiC-TiC-TiB₂ and other eutectics, which is important for optimizing the sintering temperature, material design and prediction of properties of many materials for high temperature applications including wear, aggressive, impact and radiation conditions. A vast identified group of eutectics with number of components n ≥ 2 has reduced eutectic temperature Т_eut. (in some sistems reducing reaches 1200 °C). Noted, that increasing of n suppresses grain growth, which is particularly important for developing nanostructured ceramics via pressureless sintering and for controlling the ceramic's performance. Multiphase ceramics (SiC-TiC-TiB₂, B₄C-SiC-Me^dB₂, B₄C-W₂B₅-Me^dB₂, B₄C-LnB₆-Me^dB₂, etc.) feature improved mechanical parameters and high wear and impact resistance.

Abstract: The 6xxx series alloys are well known for desirable combinations of high strength, weldability, corrosion resistance and formability. This paper investigates the influence of chemical composition on the solution heat treatment parameters of rheo-high pressure die cast (R-HPDC) 6xxx series aluminium alloys. The presence of copper in the 6xxx series aluminium alloys affects the solution heat treatment by promoting incipient melting. The incidence of incipient melting is investigated for the R-HPDC alloys using Differential Scanning Calorimetry (DSC) and optical microscopy. R-HPDC is known to produce surface liquid segregation and centre-line liquid segregation when processing the alloys and these areas are the most susceptible to incipient melting. The applicability of single and multiple step solution heat treatments are investigated. The alloys used for this study include the Cu-free alloy 6082, as well as the Cu-containing alloys 6013 and 6111.

Abstract: Ce and Ca co-doped LiGdF₄-LiF eutectics were grown and their directionally solidified eutectic (DSE) system has been investigated. In these eutectics, apart from the expected 305 nm emission of the regular Ce³⁺, 310 nm emission of the Gd³⁺ and Ce³⁺-perturbed emission around 320-380 nm was observed. Ce³⁺-perturbed emission at 340 nm shows the intrinsic decay time of about 27 ns. In photoluminescence mechanism the observed decay time shortening of the regular Ce³⁺ and Gd³⁺ centers point to the energy transfer in the sequence the regular Ce³⁺→ (Gd³⁺)_n→ the perturbed Ce³⁺ sites.

Abstract: Eutectic alloys from the ternary system Al-Cu-Ag are excellent model alloys for the investigation of coupled eutectic growth, not only because most materials properties are well known but also because the system offers a rich variety of crystal structures and crystal orientation relationships (ORs) being associated to distinct minima of the solid-solid interface energy. This paper describes three research topics specifically related to bulk lamellar Al-Al₂Cu eutectics, e.g. the maze-to-lamellar transition during early growth, the role of fault lines during lamellar spacing selection close to the pinch-off limit and the onset of eutectic cell formation above the constitutional supercooling limit. These topics are central to the microgravity experiments SETA presently being prepared for the MSL / SQF.

Abstract: Inoculation of casting used to improve the microstructure and the properties of the component. Depending upon the area of application, gray cast iron has different microstructure and mechanical properties. The type and amount of the inoculation result in shape and orientation differences of the flake graphite. The Linear Variable Differential Transformer (LVDT) shows a variation in displacements change during the solidification. Temperature measurement used to analyze cooling curves and microstructural analysis of sample to examine the physical differences. Thermal analysis compared with the experimental results and microstructural study for describing the variation in area fraction and shape of graphite. The experimental result indicates contraction in austenite formation region, and expansion in eutectic formation region. The effect of the inoculant and the superheat temperature shows a variation in degree of expansion/contraction and cooling rates of the experiments. The comparisons between the experimental and the theoretical results have been done. Combining the theoretical and experimental results, it resembles a difference in eutectic formation region, and it needs carful investigation in future works.

Abstract: The directional solidification behavior of a first generation single crystal superalloy CMSX-6 was investigated. The solidification rate range in 25μm/s to 100μm/s and a thermal gradient G of 30K/cm were used for the present study. The experimental results show that the primary dendrite arm space (PDAS) decreased from (432±8) μm to (369±4) μm as the solidification rate increased, and the sizes of the eutectic pools also decreased as the solidification rate increased. And the volume fractions of eutectic γ/γ' were about 7% to 9% with different solidification rate. The γ/γ'- eutectic was comprised with coarse γ' phase and fine γ/γ' network. The morphology of the γ/γ’ eutectic supported the possibility that the solidification of γ/γ’ eutectic initiates with the formation of fine γ/γ’.