FORMATION OF BETA-FESI2 FROM THE SINTERED EUTECTIC ALLOY FESI-FE2SI5 DOPED WITH COBALT

The formation and growth of β-FeSi2from the sintered eutectic alloy consisting of ε-FeSi and α-Fe2Si5doped with cobalt has been studied by X-ray analysis and measurements of electrical resistivity and thermoelectric power for annealing temperatures from 1073 to 1173 K. The electrical resistivity increased with increasing the amount of the β phase. Two peaks were found on the isochronal annealing curve of the electrical resistivity vs. temperature plot at 1115 and 1135 K, with a minimum value at Tc= 1128 K. X-ray analysis showed that two different mechanisms are operative on the formation of the β phase, in a similar way to the case of the undoped FeSi2. One is the two-stage transformation of α → β + Si (decomposition) and subsequent Si + ε → β below TC, and the other is a simple transformation of α + ε → β (peritectoid reaction) above TC. Thus, the single β phase was obtained with the former mechanism at a considerably lower temperature and shorter annealing time than with the latter mechanism. © 1990.