Experimental investigation of phase transformations in the La-Fe and La-Fe-C systems.

Phase equilibria in the La-Fe-C system at crystallization were studied and the binary La-Fe system was reinvestigated using DTA, X-ray diffraction, SEM and electron probe microanalysis. Using the results, the binary La-Fe phase diagram has been redrawn and liquidus and solidus projections for the La-Fe-C system constructed, for the first time, covering the whole concentration range. There is no stable miscibility gap in the liquid phase of La-Fe system, according on our results. The La-Fe system shows a simple eutectic at 88 at.% La. The eutectic temperature was measured to be 788 °C. No intermediate phases were found. In the ternary La-Fe-C system a ternary compound La 3.67 FeC 6 (τ) was found in equilibrium with the liquid phase and to coexist with most of the other phases in the system. Additions of carbon to La-Fe alloys caused liquid immiscibility. In this investigation, the liquid separation has been proved with clear microscopic pictures of samples showing this effect. A ternary stable liquid miscibility gap marked L 1 + L 2 develops from a metastable liquid miscibility gap in the La-Fe binary system. None of the binary intermetallic phases show any solubility of the third component. • The binary La-Fe phase diagram has been redrawn. • There is no stable miscibility gap in the liquid phase of La-Fe system. • Liquidus and solidus projections constructed for the La-Fe-C system. • A closed liquid miscibility has been established. • The ternary compound La 3.67 FeC 6 (τ) was found to solidify incongruently by peritectic reaction. [ABSTRACT FROM AUTHOR]