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Materials (Basel). 2017 Apr 15;10(4). pii: E415. doi: 10.3390/ma10040415.

Grain Boundary Character Dependence on Nucleation of Discontinuous Precipitates in Cu-Ti Alloys.

Author information

1
Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan. semboshi@imr.tohoku.ac.jp.
2
Department of Materials Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai 599-8531, Japan. semboshi@imr.tohoku.ac.jp.
3
Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan. m-sato@imr.tohoku.ac.jp.
4
Department of Materials Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai 599-8531, Japan. kaneno@mtr.osakafu-u.ac.jp.
5
Department of Materials Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai 599-8531, Japan. iwase@mtr.osakafu-u.ac.jp.
6
Department of Materials Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai 599-8531, Japan. takasugi@mtr.osakafu-u.ac.jp.

Abstract

The dependence of the grain boundary character distribution for a Cu-4 at. % Ti polycrystal alloy (average grain size: 100 µm) on the nucleation of cellular discontinuous precipitates was systematically investigated. In an alloy over-aged at 723 K, cellular discontinuous precipitates consisted of a terminal Cu solid solution and a stable β-Cu₄Ti lamellae nucleated at grain boundaries. Electron backscatter diffraction analysis revealed that the discontinuous precipitation reaction preferentially occurred at random grain boundaries with a Σ value of more than 21 according to the coincidence site lattice theory. On the other hand, few cellular discontinuous precipitates nucleated at low-angle and low-Σ boundaries, particularly twin (Σ 3) boundaries. These findings suggest that the nucleation of discontinuous precipitates is closely correlated with grain boundary character and structure, and hence energy and/or diffusibility. It should therefore be possible to suppress the discontinuous precipitation reaction through control of the alloy's grain boundary energy, by means of texture control and third elemental addition.

KEYWORDS:

Cu alloy; aging; discontinuous precipitation; electron backscattering diffraction; grain boundary; misorientation; Σ value

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