Phase transformations in the Zr-rich part of the Zr-Fe system resulting from heat treatment and plastic deformation
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INTRODUCTION
SEVERAL descriptions are available for the Zr-Fe system, especially for the Zr-rich regionJ -s According to Hansen and Anderko, 1 the bcc /3-phase at a concentration of 2.5 wt pet Fe undergoes a eutectoid transformation at 1073 K (800 ~ into the hcp a-phase and the intermetallic ZrFe2, which is a Laves phase of Cu2Mg structure. The a-phase is a solid solution with a maximum solubility of -0.02 wt pct Fe at the eutectoid temperature. Rhines and Gould2 reported two additional intermetallics, Zr2Fe and Zr4Fe. Mrssbauer measurements by Babikova et al. 3 confirmed the existence of Zr2Fe and ZrFe2 only. Kuzma et al. 4 identified Zr2Fe while Malakhova et al. 6 and Aubertin et al. 8 conf'Lrmed the presence of another phase Zr3Fe in addition to the Zr2Fe and ZrFe2 intermetallics. The structure of Zr2Fe was found to be bet of CuA12 type5,s and Zr3Fe is orthorhombic. 6's The divergence of the above findings is apparently associated with possible contamination of the alloys investigated by other elements such as oxygen or nitrogen, 6"s'9 which influences the process of phase formation and the final microstructure. Metallographic analysis ~~ yielded t h e solubility of iron in zirconium 0.033 at. pet (0.02 wt pet) at 1073 K (800 ~ 0.02 at. pet (0.012 wt pet) at 973 K (700 ~ and zero at room temperature. The highest iron content for which full transformation into the a-martensitic phase is possible has not yet been determined. There are even implications2 that a,, (martensite) is unobtainable in a state of Fe supersaturation, unlike the case of Ti-Fe which is a system closely similar to that of Zr-Fe? ~ B.Z. WEISS, on leave of absence with IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, is Professor, Department of Materials Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel. M. BAMBERGER, Senior Lecturer, and M. M. STUPEL, Visiting Senior Lecturer, are with the Department of Materials Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel. Manuscript submitted September 9, 1985.
METALLURGICALTRANSACTIONSA
The limited information available indicates that an iron content of - 4 . 1 wt pet 2 or 5.5 wt pct ~2does not suffice for complete stabilization of the/3-phase at room temperature after quenching from the/3-region. In order to obtain/3 at room temperature, additional/3 stabilizers have to be added such as Ti 13or Mo, as was done in the present study. In Zr, Ti, and Hf alloys under certain conditions the metastable to-phase can be formed through the/3,, ~ / 3 + to transformation: athermal to-phase during quenching from the 13 region or thermal to-phase in the/3 aging process. The cooling rates and iron concentrations necessary for w-phase formation in the Zr-Fe system are not yet established. A series of studies 14-17showed that by application of high pressure to Zr(a) or Ti(a) the a-phase may transform to to-phase. The mechanism for this transformation was formulated and the orientation relationship was determined. 16.17 It was suggested that the
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