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

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, αCo, Cr5Al8 (γ3 and γ1 phases), CoAl, Co2Al5 binary compounds and the ternary compound τ5 take part in phase equilibria. The monoclinic ternary compound τ5 forms by peritectic reaction L + γ1 + Co2Al5 ↔ τ5 at 1065 °C. Four invariant four–phase reactions and one invariant three–phase 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.