Eutectic transformation L ↔ Zr6Fe23 + Fe(τ) in the Fe-Zr system

The knowledge of the phase diagram of the Fe-Zr system is important because Fe is always present as an impurity in commercial Zr-base nuclear grade alloys. This diagram has four intermetallic compounds, namely Zr3Fe, Zr2Fe, ZrFe2 and Zr6Fe23. ZrFe2 with a cubic Laves C15 structure melts congruently at 1673 deg C and Zr6Fe23 with a cubic Th6Mn23-type structure is a product of the peritectic ZrFe2 + L↔Zr6Fe23 reaction at 1482 deg C. As a part of the work on the Fe-rich portion of the system, the eutectic transformation L↔Zr6Fe23 + Fe(τ), its temperature and its composition have been studied. In order to find the eutectic temperature, sample of Zr15Fe65 and Zr4Fe96 were thermally treated at the temperature higher and lower than 1337 deg C, which was reported in the last revision of the diagram (1988). It was observed that samples treated at 1345 deg C, 1340 deg C, 1335 deg C and 1325 deg C partially melted while those treated at 1320 deg C did not. An eutectic temperature of (1325 ±5) deg C could be determined from the results of metallographic, X-ray and microanalysis experiments. The composition of the eutectic was determined to be (90±1)at % Fe, with the electron microprobe, by automatically averaging results on regions 10μm long. (Author)