Experimental and Theoretical Measurements of the Evolution of Embryos Before and During the Nucleation Stage |
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Authors: | Yasuhiro Aruga Hidenori Nako |
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Affiliation: | (1) Materials Research Laboratory, Kobe Steel, Ltd, 1-5-5 Takatsukadai, Nishi-ku, Kobe 651-2271, Japan |
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Abstract: | The early precipitation of a Cu-Ni-P alloy during aging for 100 ks at 523 K and 623 K (250 °C and 350 °C) after solution
treatment has been characterized using a three-dimensional atom probe (3DAP) and transmission electron microscopy (TEM). It
is shown that the particles have a wide range of Ni/P ratios when they are relatively small, whereas larger ones exhibit a
narrow distribution of the Ni/P ratio, approaching the ratio of approximately two. The threshold radii that show the steady
Ni/P ratio are around 1.5 nm and 2.0 nm for the materials aged at 523 K and 623 K (250 °C and 350 °C), respectively. These
values are in a reasonably good agreement with the critical nuclei radius estimated from classic nucleation theory. It is
suggested that the particles with steady Ni/P ratios of approximately two are considered to be the equilibrium precipitates
formed through nucleation, whereas the extremely fine particles with varying Ni/P ratios, detected by the 3DAP experiments,
indicate subcritical clusters or embryos. |
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