The Influence of Cr Concentration on the Phase Composition and Properties of a Directionally Crystallized Ternary System Cr–Fe–Si Before and After Annealing

Abstract

This paper describes the phase composition, morphological, chemical, and crystallographic properties of silicide phases in Cr–Fe–Si alloy ingots obtained through directional solidification, both before and after annealing. The samples had a general formula Cr_xFe\(_{{1-x}}\)Si₂ with x = 0.1, 0.2, 0.3, and 0.4. Characterization of samples using various techniques (powder X-ray diffraction, transmission and scanning electron microscopy with electron backscatter diffraction, energy dispersive X-ray spectroscopy) showed that the use of a higher Cr concentration (x = 0.3 and 0.4) leads to suppression of the formation of the ε-FeSi metallic cubic phase. The amount of Cr involved in the substitution of Fe in α-, β-, and ε-Fe silicides does not depend on the nominal Cr concentration introduced into initial melts. Unlike the samples that underwent the free crystallization process, neither pure Si nor some other silicides (for example, Cr₅Si₃) or pure Si were found in the ingots of directional crystallization. The orientation relationships between the phases and the directions of growth of precipitates before and after annealing were established. Electrical conductivity, Seebeck coefficient and power factor were determined for the as grown and annealed ingots.