Partial Redetermination of the Fe-W Phase Diagram
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NTRODUCTION
A. Context
THE Fe-W binary system is the base of several technologically appealing alloys. In particular the metallurgical industry benefits from a wide variety of tungsten alloys and compounds (hard and refractory alloys, high speed steels, tool steels, etc.). In 1933, Sykes et al.[1] proposed an equilibrium phase diagram of the Fe-W system. Since then, many experimental investigations were carried out, the results of which have been presented in the review articles by Raynor et al.[2] and Nagender et al..[3] Several versions of the experimental diagram are currently proposed. The main controversy concerns the extension of the l-Fe7W6 phase and the existence of the k-Fe2W Laves phase. Henig et al.[4] and Hofmann[5,6] found a new intermetallic phase d-FeW. Apart from these intermetallic phases, a gamma-loop occurs which separates the austenite phase c-Fe and the ferrite phase a-Fe. Solubility data of W in a-Fe have been reported by several authors[1,7–11] and most of it is reasonably well described by the thermodynamic modeling from Gustafson.[12] However, experimental information obtained in the ternary Co-Fe-W system, in particular the phase boundaries of the a-Fe phase at 1653 K (1380 °C), are not well accounted for by the calculation in the Fe-W side of the ternary. For example, the measured solubility of W in a-Fe is of 7.96 at. pct W at 1653 K (1380 °C) in a Fe-6Co-11.5W (at. pct W) sample, which is inconsistent with a calculated value of 9.45 at. pct W in the ANNIE ANTONI-ZDZIOBEK, is with SIMAP, INP GrenobleCNRS-UJF, BP 75, 38402 Saint-Martin d’He`res, France. Contact e-mail: [email protected] THIERRY COMMEAU, is with the Eurotungste`ne, Eramet Group, 9 Rue Andre´ Sibellas, BP 152X, 38100 Grenoble Cedex 9, France. JEAN-MARC JOUBERT, Chimie Me´tallurgique des Terres Rares, Institut de Chimie et des Mate´riaux Paris-Est, CNRS, Universite´ Paris-Est Cre´teil, 2-8 Rue Henri Dunant, 94320 Thiais Cedex, France. Manuscript submitted August 3, 2012. Article published online February 20, 2013 2996—VOLUME 44A, JULY 2013
binary Fe-W system.[13] It would be in agreement with solid solubility data of W in a-Fe in the binary Fe-W system lower than the calculated values.
B. Literature Survey According to Raynor et al.,[2] on the basis of the work of Kirchner et al.[10] and Sinha et al.,[9] two intermetallic phases l and k exist in the Fe-W system. The l phase is formed by peritectic decomposition at 1913 K (1640 °C). The k phase has a narrow solubility domain between 33.4 and 34.0 at. pct W. Hofmann[5,6] and Henig et al.[4] characterized a new intermetallic phase d-FeW in alloys containing 15, 27 and 40 at. pct W annealed at 1273 K (1000 °C) for periods of time of more than 100 days. This phase is described as formed by a peritectoid reaction at 1488 K (1215 °C). The k-Fe2W phase is described as a transitional metastable phase resulting from the decomposition of the l phase around 1473 K (1200 °C). According to the experimental work of Henig et al.[4] and Hofmann,[6] the d phase is included in the
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