Minoru Otaguchi1, Yasuji Yoshida2 and Atsushi Oguchi1
1National Research Institute for Metals, Tokyo
In order to study the influence of hydrostatic pressure on the processes of recrystallization and aging of metallic materials, isothermal heat treatments have been done on a cold rolled OFHC copper and a Cu-Be alloy under 0.1 MPa and 800 MPa, and change in hardness with the holding time has been discussed. The results obtained are as follows:
(1) No evident qualitative difference in structure due to pressure was observed in the OFHC copper after the primary recrystallization.
(2) The change in hardness during the primary recrystallization was delayed by applying high hydrostatic pressure, and the time necessary for obtaining a given value of hardness under 800 MPa was about 2.9 times as large as the time under 0.1 MPa. This value is close to 2.5 calculated by assuming that the activation volume of self-diffusion of copper is about 0.7 \BarV (\BarV is the molar volume of copper).
(3) As for the Cu-Be alloy, the increase in hardness was also delayed under high hydrostatic pressure. The time required for coming up to a certain hardness number under 800 MPa was about 2 times as large as the time under 0.1 MPa. Also in this case, a similar value of about 2.2 was calculated by assuming that the activation volume of diffusion of Be atom in copper is 0.55 \BarVCu+0.15 \BarVBe (\BarVCu and \BarVBe are the molar volumes of copper and beryllium, respectively).
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