Materials Transactions Online

Transactions of the Japan Institute of Metals, Vol. 12 No. 3 (1971) pp.206-213
© 1971 The Japan Institute of Metals

Electron Microscopy Study of the Precipitation Processes in Cu-2 wt% Be Alloy*

Ken'ichi Shimizu**, Yasuharu Mikami***,
Hiroyasu Mitani**** and Kazuhiro Otsuka**

In order to make clear the precipitation processes in Cu-Be alloy, the structural changes upon ageing of the 2 wt% Be alloy were examined in detail through an electron microscopy in particular by the use of the selected-area electron diffraction technique. The change in electron diffraction patterns with increasing ageing time or temperature was as follows. In the earliest stage, long streaks appeared in the <001> directions due to the formation of G. P. zones. Upon prolonged ageing, the streaks become shorter and intensity maxima appeared at about 2/3 of {002} reciprocal lattice vectors. This stage is distinct from the G. P. zone formation and may correspond to the formation of the γ'' phase. The structure of γ'' is considered to be a body-centered tetragonal, with Cu atoms at the corner and Be atoms at the body-center, and is different from that proposed by Geisler et al. Ageing at higher temperatures caused another superlattice reflection (CuAu(II) type, γ') to appear and 2/3 reflections mentioned above to split. This splitting corresponded to the formation of the γ phase. From these observations, it has been concluded that the ageing sequence is α→ G. P. zone →γ''→γ'→γ.
The structure of the final precipitate γ was identified to be the same as that of the equilibrium phase with the lattice constant 2.71 Å. Then a new orientation relationship between the γ and α has been proposed, such that

{103}γ//{113}α,<010>γ//<1\bar10>α.
Among several orientation relationships reported so far, only this one was consistent with our experimental results. In spite of the identity in structure, the final precipitates γ were associated with strain contrast around themselves, in contrast to the equilibrium phase. This fact suggests that the transformation γ' to γ might be martensitic in the nucleation stage. The mechanism of γ' to γ transformation is discussed along this line and from the viewpoint of coherency.

(Received January 19, 1971)


* This paper was read before the Annual Meeting of the Japan Institute of Metals, October, 1970, and published in Japanese in J. Japan Inst. Metals, 34 (1970) 1108.

** The Institute of Scientific and Industrial Research, Osaka University, Suita, Osaka, Japan.

*** Graduate School, Osaka University. Present address : Sumitomo Electric Industries Ltd., Itami, Osaka, Japan.

**** Faculty of Engineering, Osaka University, Suita, Osaka, Japan.

Citing Article(s):

  1. Materials Transactions, JIM, Vol.36 No.9 (1995) pp.1118-1123 :
    Effect of Quenching Temperature on the Intragranular and Cellular Precipitations in Cu-1.5%Be Binary Alloy
    Masamichi Miki and Yoshikiyo Ogino
  2. Materials Transactions, JIM, Vol.39 No.4 (1998) pp.455-462 :
    Influence of Grain Size and Quenching Rate on the Age-Hardening Behavior of Cu-2%Be Alloy
    Masamichi Miki*, Atsushi Tenma*, Shuhei Ishikawa**
    and Yoshikiyo Ogino*

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