A Revision of the Al-rich Region of the Sm-Al Phase Diagram: The Sm 3 Al 11 Phase

  • PDF / 236,236 Bytes
  • 3 Pages / 593.972 x 792 pts Page_size
  • 110 Downloads / 229 Views

DOWNLOAD

REPORT


Section I: Basic and Applied Research

A Revision of the Al-Rich Region of the Sm-Al Phase Diagram: The Sm 3 Al 11 Phase S. Delsante, R. Raggio, G. Borzone and R. Ferro

(Submitted November 14, 2006) Phase equilibria in the Al-rich region of the Sm-Al binary system has been revised and updated: it has been confirmed that Sm3Al11 is a congruently melting phase which, on cooling, undergoes catatectic decomposition Sm3Al11 M liquid + SmAl3.

Keywords

Al-Sm system, Al-Sm phase diagram, experimental phase equilibria, rare earth intermetallics

1. Introduction While most of the R-Al systems are quite well established, the Sm-Al still needs investigation because of some uncertainties emerging from a comparison of literature data. A comprehensive examination of R-Al diagrams formed by the trivalent rare earth elements with Al shows progressive and systematic variations in the constitutional properties.[1,2] Light rare earth R-Al diagrams present the Alrichest R3Al11 phase,which is absent in the heavy rare earth R-Al diagrams. The first partial phase diagram for the Sm-Al system is reported in literature by Buschow and Van Vucht[3] and Casteels,[4] where only the Al-rich region (~66-100 at.% Al) was investigated. The Al-richest part (96-100 at.% Al) of the diagram was subsequently studied by Kononenko and Golubev.[5] The diagram shows four intermetallic line compounds stable at room temperature and the Sm3Al11 phase with a congruent melting and a catatectic decomposition at 1066 C. This part of the phase diagram is significantly different from the corresponding regions of other R-Al systems, wherein the R3Al11 phases have been described as stable down to room temperature with an aMb transformation in the solid state. In all the R-Al systems the Al-richest congruent melting compounds are RAl2 and the other Al-richer phases have a peritectic or peritectoidal formation. The peritectoidal formation of SmAl3 is characteristic of the light rare-earths (La, Ce, Pr, Nd). Owing to a lack of data and the thermodynamically improbable shape of the liquidus curve in this diagram, a series of thermal analyses was performed by Saccone et al.[6] and thermodynamic investigations by Borzone et al.[7]; this has made it possible to re-define and calculate S. Delsante, R. Raggio, G. Borzone, and R. Ferro, Dipartimento di Chimica e Chimica Industriale, Universita` di Genova, Consorzio INSTM-UdR di Genova, Via Dodecaneso 31, 16146 Genova, Italy; Contact e-mail: [email protected]

240

the Sm-Al phase diagram. In the paper by Saccone et al.[6] the congruent melting of Sm3Al11 was confirmed, however, suggesting a melting temperature of 1380 C, lower than the value ~1450 C as earlier reported in literature.[3,4] A thermal effect was observed around the Sm3Al11 composition at about 1070 C. Nevertheless, it was not possible to definitely attribute this effect either to a catatectic reaction or to an allotropic transformation (as observed in the alloys of other light rare earths). In the same paper a thermodynamic optimization was performed by alte

Data Loading...