C.T. Rios

Influence of the growth rate on the microstructure of a Nb–Al–Ni ternary eutectic

Abstract Solidification of a eutectic alloy from the melt produces composite materials, composed of two or more solid phases. Processing by directional solidification presents interesting and different properties when compared to the properties of its constituent phases. One of the ternary systems that has been little studied and exhibits eutectic reaction resulting in three intermetallic phases is the Nb–Al–Ni ternary system, which involves the NbAl3, Nb2Al and AlNbNi phases. Eutectic alloys from this system were processed in an arc melting furnace and in a Bridgman equipment for directional growth. The objective of the experiments was to determine the influence of growth parameters on the eutectic microstructure. The mechanical behavior of the composite was studied through microhardness testing and fracture toughness using Vickers indentation technique. Microstructural characterization and chemical compositions of the samples were investigated by using optical and scanning electron microscopy with energy dispersive spectroscopy.

Primary dendrite spacing as a function of directional solidification parameters in an AlSiCu alloy

Abstract Dendritic growth is of considerable importance, since this phenomenon controls solute segregation and hence, the material mechanical properties. The main objective of this investigation is to present a directional solidification study of the Al-8.5 wt% Si-2.5 wt% Cu alloy with dendritic growth. Such an alloy was processed at several growth rates and thermal gradients and an investigation of the dendritic growth was carried out. The solidification microstructure was studied by comparing experimental dendrite spacings with results furnished by theoretical models. Such a comparison allows one to calculate primary dendrite spacing as a function of growth rate, thermal gradient and alloy thermophysical parameters.

Directional growth of Al-Nb-X eutectic alloys

Abstract Composite materials show attractive properties resulting from the combination of properties of their constituent phases. Special interest has been devoted to the intermetallic matrix composites, since they have been recognized as potential substitutes for the superalloys. An interesting and efficient means of preparation of the composite materials is the directional solidification of eutectic alloys. The eutectic microstructure of many systems possesses inherent thermal stability and may result in a composite material, with an aligned, finely dispersed microstructure. The goal of this study was to evaluate the influence of a ternary element addition (Cu, Si, Ni, Ti and Cr) on the microstructure of the Al–Nb eutectic system. Microstructural characterization of the as-cast and directionally solidified samples, revealed changes in the eutectic morphology from cellular to dendritic and from lamellar to rod or globular structure. Also, it was confirmed that the alloy containing 57.18% Al–40.40% Nb–2.42% Ni in atomic% exhibits a ternary eutectic reaction. The directional solidification of this alloy resulted in a regular three-phase eutectic microstructure.

Evaluation of the solid/liquid interface undercooling during Sn-Se Eutectic growth

The Sn-Se eutectic solidification allows one to obtain a lamellar structure, formed by SnSe and SnSe2 compounds, which are p and n semiconducting types, respectively. The SnSe-SnSe2 eutectic composite is a promising material to be used in photovoltaic device manufacturing. In a lamellar eutectic microstructure, the main parameter, which governs many of its characteristics, is the lamellar spacing. Such a parameter is primarily a result of the undercooling at the solid/liquid interface, which depends on the growth rate and the eutectic system properties. In this work, the Sn-Se alloy corresponding to eutectic composition was studied by using DSC thermal analysis and directional solidification at several growth rates in a vertical Bridgman-Stockbarger unit. The objective of the experiments was to investigate the influence of the growth rate on the growth undercooling, as well as on the eutectic microstructure. The microstructure analysis showed that a very regular and aligned structure formed by the SnSe and SnSe2 solid phases can be produced. By using the classic eutectic growth theory developed by Jackson and Hunt, the experimental results obtained led to the evaluation of a relationship among growth rates, eutectic growth temperature and lamellar spacing.