Yukiya G. Nakagawa1, Ken-ichi Hirano2 and Shigeyasu Koda3
1Department of Materials Science, Faculty of Engineering, Tohoku University; now, at Department of Metallurgical, Mechanical and Aerospace Engineering, University of Delaware, Newark, Del., U.S.A.
Decomposition in the supersaturated solid solution of Fe-11.3 atomic percent Be alloy has been investigated by optical and transmission electron microscopic observations, thermal analysis, hardness test and electrical resistance measurement, in comparison with the results of the X-ray structural measurements by the previous workers.
A clear difference has been confirmed between the sequence of structures for ageing temperatures below 400°C and above 500°C. The age hardening below 400°C can mainly be attributed to the massive short range order, the pseudo-FeBe L 20 order, the Fe3Be DO3 order and the side-band structure (sinusoidal modulation of composition), which were detected by the previous X-ray measurements and confirmed by the present specific heat and electrical resistance measurements. The age hardening above 500°C can be attributed to the continuous and the discontinuous precipitation.
Kinetic analysis of the heat evolution in the specific heat versus temperature curves has shown the activation energy for the formation of DO3 order from L 20 order to be about 25 kcal/mol which appears to be reasonable as for the migration of Be atoms in the bcc lattice of Fe.
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