Phase Equilibria in the Al-Cr-Co System in the Range of Compositions 0-70 at.% Al

Abstract

Phase equilibria during solidification in the Al-Cr-Co system in the range of compositions 0-70 at.% Al were studied using optical microscopy, scanning electron microscopy, electron probe microanalysis, differential thermal analysis and x-ray diffraction. Solidus and liquidus surfaces, a melting diagram as their superposition, a Scheil diagram for solidification, as well as series of isopleths were constructed for the first time. Solid solutions based on Cr, aCo, Cr 5 Al 8 (c 3 and c 1 phases), CoAl, Co 2 Al 5 binary compounds and the ternary compound s 5 take part in phase equilibria. The monoclinic ternary compound s 5 forms by peritectic reaction L ? c 1 ? Co 2 Al 5 $ s 5 at 1065°C. Four invariant four-phase reactions and one invariant threephase reaction involving liquid take place at 1280, 1175, 1110, 1065 and about 1480°C, respectively. Isopleths 10, 20, 30 and 40 at.% Al as well as 40 at.% Cr demonstrate peculiarities of the phase diagram.