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In the present work the fluxing technique was applied to the Sn–51 wt.% Se hypoeutectic alloy. The aim was to study the influence of the undercooling on the microstructure of this alloy, particularly concerning the formation of oriented microstructure and even some metastability occurrence. High undercooling (63 °C) was achieved for the primary SnSe phase leading to an oriented microstructure in the firstly solidified region. Although the undercooling for the eutectic was not so high (19 °C) morphological changes were observed. The rapid movement of the interface interfered with cooperative eutectic growth producing an irregular eutectic in the first region to solidify followed by a fine lamellar and directional eutectic. In order to detect some supersaturated solid solution in the SnSe phase a precise lattice parameter measurement was done from the accurate performed X-ray diffraction (XRD) on the firstly solidified region of the sample. [Copyright &y& Elsevier]

As the Sn-Se eutectic solidification produces a lamellar structure, formed by SnSe and SnSe2 compound, which are p and n semiconducting type, respectively, the SnSe-SnSe2 in situ composite is a promising material to be used in photovoltaic device manufacturing. In this work, the Sn-Se alloys corresponding to the eutectic composition as well as to SnSe and SnSe2 composition were processed by direction solidification at several solidification rates in a vertical Bridgman-Stockbarger crystal growth unit. The aim of the experiments was to evaluate the eutectic microstructure behavior as a function of directional solidification parameters. The obtained microstructures were analyzed by using X-ray diffraction and scanning electron and optical microscopies. The results obtained show that a very regular and aligned structure formed by the SnSe and SnSe2 solid phase can be achieved. It was found that the presence of imperfections in the eutectic microstructure depends on the growth rate, and mainly, on the alloy homogenization process. [ABSTRACT FROM AUTHOR]

Highlights: [•] TiO2 nanotubes array were grown on Ti, Ti–6Al and Ti–6Al–7Nb (w/w) alloys by anodization. [•] Morphology of oriented TiO2 nanotubes grown on as-prepared and heat treated Ti alloys was compared. [•] On α+β Ti alloys, regular and ordered nanotubes layers were formed preferentially onto α phase. [ABSTRACT FROM AUTHOR]

The effect of the growth condition on the microstructure and mechanical behaviour of the NiAl–Mo eutectic alloy was investigated. Samples of the eutectic alloy were prepared using an arc furnace under argon atmosphere and then directionally solidified. The samples directionally solidified showed regular and aligned eutectic microstructure. Compression tests were performed at room temperature and 1173 K. Vickers hardness was determined at several temperatures, from room temperature to 1150 K. Mechanical properties of NiAl were also determined. Results showed that when the growth rate is gradually increased from 8 to 50 mm/h the aligned microstructure presents higher fibre density, which leads to higher strength level at room temperature, while further increase in the growth rate causes the microstructure the loose regularity. NiAl presents a well defined mechanical behaviour transition, while the NiAl–Mo eutectic alloy softens almost linearly. The highest yield strength value of NiAl–Mo was found to be about 1200 and 300 MPa at room temperature and 1173 K, respectively. [Copyright &y& Elsevier]

Thixoforming is a typical semisolid processing route for the production of affordable near-net shape metallic components. In this study, Ti-Cu alloys specifically designed for thixoforming were evaluated to determine their microstructural evolution in the semisolid state. Ti-(25, 27, 29)Cu (wt.%) alloys were prepared by voltaic arc melting, homogenized, and then hot worked prior to isothermal heat treatment at 1035 °C. Rapid quenching allowed for the investigation of “frozen” semisolid microstructures. The results indicated the formation of fine grained globular microstructures in all the alloys under study. This was attributed to the deformation process, which was able to break up the dendrites resulting from solidification. The liquid fraction increased with Cu content and its values were consistent with those predicted under equilibrium, although evidence of some nonequilibrium liquid was still present during the time period of analysis. Lastly, coarsening rate constants ( K ) exhibited low values, indicating stable semisolid microstructures. [ABSTRACT FROM AUTHOR]

Abstract: The performance of Ti alloys can be considerably enhanced by combining Ti and other elements, causing an eutectic transformation and thereby producing composites in situ from the liquid phase. This paper reports on the processing and characterization of a directionally solidified Ti–Fe eutectic alloy. Directional solidification at different growth rates was carried out in a setup that employs a water-cooled copper crucible combined with a voltaic electric arc moving through the sample. The results obtained show that a regular fiber-like eutectic structure was produced and the interphase spacing was found to be a function of the growth rate. Mechanical properties were measured using compression, microindentation and nanoindentation tests to determine the Vickers hardness, compressive strength and elastic modulus. Directionally solidified eutectic samples presented high values of compressive strength in the range of 1844–3000MPa and ductility between 21.6 and 25.2%. [Copyright &y& Elsevier]

Abstract: An attractive alternative method for the manufacture of high temperature structural materials may be achieved from a eutectic transformation found in the Fe–Al–Nb system, which generates the (Fe, Al)2Nb and (Fe, Al, Nb)ss solid phases. Eutectic and off-eutectic samples from the Fe–Al–Nb system were prepared by arc melting under argon atmosphere, which were subsequently directionally solidified using a vertical Bridgman crystal growth unit. The ingots obtained were investigated using optical and electron scanning microscopy with the purpose to evaluate the effect of the growth condition on the microstructure. Primarily, the growth mode of the (Fe, Al)2Nb/(Fe, Al, Nb) eutectic was considered by examining off-eutectic samples. The solidification experiments carried out under different conditions revealed that the microstructure of this system is very sensitive to a growth rate variation. At a low growth rate, the eutectic microstructure was regular, even though several types of defects were found. As the growth rate was increased, a transition from lamellar to fibrous morphology was observed. Some aspects of this transition were also evaluated. [Copyright &y& Elsevier]

Abstract: Despite presenting potential as high-temperature structural material, the NiAl intermetallic compound cannot be easily employed due to its low room temperature fracture toughness and poor creep strength. A solution for such a problem is combining such a compound with other phase using a eutectic transformation, as in the case of the NiAl–NiAlNb eutectic structure. In this study, several samples containing Ni, Al and Nb were arc melted in order to evaluate the eutectic composition of this transformation, as well as the temperature at which it occurs. The resulting phases were the B2 NiAl and the Laves phase NiAlNb. It was found that the eutectic alloy occurs close to 16.0at% Nb and the eutectic transformation temperature is 1487°C. The amount of NiAl phase clearly decreases when the Nb content is raised. Thus, hypoeutectic alloys present NiAl dendrites with NiAlNb precipitated at the grain boundaries while hypereutectic alloys present primary dendrites of NiAlNb. The eutectic alloy was directionally solidified at growth rates varying from 5.0 to 50.0mm/h. As expected, the lamellar spacing was found to decrease as the growth rate was increased. [Copyright &y& Elsevier]