Precipitation in a Cu-26Ni-8Fe Alloy

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  • Cu-26Ni-8Fe合金における析出
  • Cu 26Ni 8Fe ゴウキン ニ オケル セキシュツ

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Continuous and discontinuous precipitations were investigated for a Cu-26Ni-8Fe alloy aged isothermally in the temperature range of 673 to 1023 K, by means of optical and electron microscopic observations, hardness measurement and X-ray diffraction analysis. The results obtained are as follows:<BR>(1) During the earlier ageing stages, wavelength of the modulated structure remained a constant value (8∼9 nm) and then increased the (time)1⁄3 law.<BR>(2) Discontinuous precipitations were observed when the specimens were aged in the temperature range of 673 to 853 K. The growth rate of it greatly decreased with increasing temperature.<BR>(3) Volume fraction of discontinuous precipitates, f, could be represented by Johnson-Mehl’s equation; f=1−exp(−btn), and the n-values were 1.0 at 673 K and 0.8 at 723 K. But above 723 K, this equation could not be applied during the later ageing stages.<BR>(4) The above described temperature dependence of the discontinuous precipitation may be caused by the progress of continuous precipitation.<BR>(5) The apparent activation energy of continuous and discontinuous precipitation process was about 188 kJ/mol and 84 kJ/mol, respectively.

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