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Thermal decomposition of mechanically alloyed nanocrystalline fcc Fe60Cu40

Published online by Cambridge University Press:  31 January 2011

J. Y. Huang ,
Y. D. Yu ,
Y. K. Wu ,
H. Q. Ye  and
Z. F. Dong
J. Y. Huang
Affiliation:
Laboratory of Atomic Imaging of Solids, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, People's Republic of China
Y. D. Yu
Affiliation:
Laboratory of Atomic Imaging of Solids, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, People's Republic of China
Y. K. Wu
Affiliation:
Laboratory of Atomic Imaging of Solids, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, People's Republic of China
H. Q. Ye
Affiliation:
Laboratory of Atomic Imaging of Solids, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, People's Republic of China
Z. F. Dong
Affiliation:
Laboratory of RSA, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015, People's Republic of China
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Abstract

A ferromagnetic and supersaturated fcc Fe60Cu40 solid solution was prepared by mechanical alloying (MA). The phase transformations of the as-milled Fe60Cu40 powder upon heating to 1400 °C and subsequently cooling to room temperature were characterized by differential thermal analysis (DTA) and thermal magnetic measurement. The fcc Fe60Cu40 solid solution decomposes into α–Fe(Cu) + γ–Fe(Cu) + Cu(Fe) upon heating from 300 to 460 °C, and on further heating, α–Fe(Cu) transforms to γ–Fe(Cu) at 640 → 760 °C; during cooling, the reverse transformation occurs from 800 → 640 °C (obtained from thermomagnetic measurement) or from 700 → 622 °C (obtained from DTA). The γ ⇆ α transformation in mechanically alloyed Fe60Cu40 nanocrystalline occurs in a wide temperature range; the transformation temperature is higher than that of the martensite transformation in as-cast Fe–Cu alloys, but is much lower than that of the allotropic transformation of pure Fe. These differences may be caused by the different fabrication process, the nonequilibrium microstructure of MA, as well as the inhomogeneous grain size in α–Fe(Cu). High resolution transmission electron microscope (HRTEM) observations carried out in the specimen after the DTA run show that N-W or K-S orientation relationships exist between α–Fe(Cu) and Cu(Fe), which also represent the orientation relationship between α–Fe(Cu) and γ–Fe(Cu) due to excellent coherency between γ–Fe(Cu) and Cu(Fe). The grain size of the α–Fe(Cu) is inhomogeneous and varies from 50–600 mm. Energy dispersive x-ray spectroscopy (EDXS) result shows that the Cu content in these α–Fe(Cu) grains reaches as high as 9.5 at. % even after DTA heating to 1400 °C, which is even higher than the maximum solubility of Cu in γ–Fe above 1094 °C. This may be caused by the small grain size of α–Fe(Cu).

Type
Articles
Information
Journal of Materials Research , Volume 11 , Issue 11 , November 1996 , pp. 2717 - 2724
Copyright
Copyright © Materials Research Society 1996

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