Low temperature diffusivity measurements in the FeNi system using STEM techniques
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TEMPERATURE (*C) 725 I
10-15
700 I
675 I
650 I
600 I
Fe- 2 0 A I - 5Si
Tcl " 10-16.
tlJ U3
5:
1. K. Oki, M. Hasaka, and T. Eguchi: Trans. Jap. Inst. Metals, 1973, vol. 14, p. 8. 2. L. Rimlinger: C. V. Acad. Sci. Paris, 1971, vol. 272(C), p. 22. 3. H. Sagane, A. Yamamura, K. Oki, and T. Eguchi: J. Jap. Inst. Metals, 1975, vol. 39, p. 1076. 4. S.M. Allen and J.W. Cahn: Acta Met., 1979, vol. 27, p. 1085. 5. R. Smoluchowski: Phys. Rev., 1951, vol. 83, p. 69. 6. D. Turnbull: Trans. AIME, 1951, vol. 191, p. 661. 7. V.E. Polishchuk and Ya. P. Selisskii: UKr. Fiz. Zh., 1969, vol. 14, p. 1722. 8. M.G. Mendiratta: Systems Research Laboratories, Inc., Dayton, OH, unpublished research, 1982. 9. M.J. Marcinkowski and N. Brown: J. Appl. Phys., 1962, vol. 33, p. 537. 10. J.E. Hilliard: in Recrystallization, Grain Growth and Textures, American Society for Metals, Metals Park, OH, 1965, p. 267.
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Low Temperature Diffusivity Measurements in the FeNi System Using STEM Techniques
ACTIVATION ENERGY ~,-~.247 kJ/mole =n 59 kcol/mole iO-le 0.95
I
I
I
1.00
1.05
1.10
1.15
C. NARAYAN and J. I. GOLDSTEIN ~/T x 103 (*K -I) Fig. 4--Temperature dependence of domain growth.-
critical temperature Tc is approached. Thus, ~r can vary by orders of magnitude. However, the present data do not show the effect of strongly varying m instead, they show a simple exp(-Q/RT)-type temperature dependence, thereby supporting the functional relationship predicted by Allen and Cahn? Thus, the phenomenological theories ~'6 which predict a linear dependence of o- on the interface velocity are not applicable to the DO3 domain growth in the present alloy. From the slope of the straight line in Figure 4, an apparent activation energy of -247 kJ/mole was calculated for the domain-growth process; this value should correspond to atomic diffusion. Since the activation energies for diffusion in the DO3 Fe-A1-Si alloys are not known, it is not possible to make a definitive statement in this regard. For the heat treatments used, only DO3 domains were observed at room temperature. The APBs had a fault vector of (1/2)a~(100); no (1/4)a~(lll) thermal APBs were observed. DO3 domain-growth kinetics exhibit a parabolic time dependence and an Arrhenius-type temperature dependence, indicating that growth is diffusion-controlled. The kinetics do not reflect the contribution of a strong temperature dependence of the surface free-energy. Thus, the surface free-energy does not control the domain growth.
This research was supported in part under Air Force Contract F33615-81-C-5059. Critical reading of the manuscript by Dr. John W. Cahn of the National Bureau of Standards and discussions with Dr. Harry A. Lipsitt of AFWAL/ MLLM are gratefully acknowledged. METALLURGICALTRANSACTIONS A
The kinetics of decomposition of austenite in Fe-base alloys are often limited by the diffusivity of the substitutional alloying element in the austenitic matrix. ~.2In Fe-Ni alloys, a knowledge of the diffusivity of Ni in Fe-Ni (Dgi) below 800 ~ is necessary to model the grow
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