Experimental Investigation of Fe–Co–La System: Liquidus and Solidus Projections

Phase equilibria in the Co–Fe–La system were studied using differential thermal analysis (DTA), X-ray diffraction analysis, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Liquidus and solidus projections and a melting diagram for this system over the whole concentration range and a Scheil diagram for solidification were constructed. The ternary compound (Co,Fe) 17 La 2 (τ) (Th 2 Zn 17 -type structure) forms by peritectic reaction L + (γCo,Fe) + Co 13 La ⇄ τ at 978 °C. This ternary compound is located along the isoconcentrate of 11 at.% La and extends from 45.8 to 79.3 at.% Co. The Co 13 La phase has the widest homogeneity region and dissolves up to 43.3 at.% Fe. The solubilities of Fe in Co 5 La, Co 7 La 2 , Co 19 La 5 , and Co 3 La 2 were established to be 10.3, 9.2, 4.7, and 3.2 at.%, respectively. The solubility of Fe in Co 1.7 La 2 and CoLa 3 according to EPMA does not exceed 1 at.%. The maximum solubility of La in (γCo,Fe) and (αCo,Fe) is determined to be less than 1 at.%.