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J. Japan Inst. Metals, Vol. 40, No. 6 (1976),

pp. 632-637

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Activation Volume of Dislocation Motion in Molybdenum

**
Koji Tanoue**^{1}, Kenji Senba^{2} and Kenji Okazaki^{1}

^{1}Department of Metallurgy, Kyushu Institute of Technology, Kitakyushu

^{2}Nippon Tungsten Co., Ltd., Fukuoka

#### Abstract:

Differential strain rate, strain rate cycling and stress relaxation tests were carried out to obtain the activation volume for dislocation motion in sintered pure molybdenum over the temperature range from 292 to 550^{°}K. By comparing the apparent activation volumes deduced from these various methods with each other, the analytical method to obtain the true activation volume, V_{0}^{*}, was discussed. V_{0}^{*} could be obtained from the stress relaxation test by extrapolating the relaxation time, t, to t=0, i.e. V_{0}^{*}=\lim _{t→}0 [2kT ∂ ln (-\dotσ)/∂ σ]_{T}. V_{F}^{*} obtained by Feltham's analysis of the relaxation data must, however, be corrected in the variation of the mobile dislocation density during relaxation to obtain V_{0}^{*}.

In the temperature range below 420^{°}K, V_{0}^{*} was found to be less than about 100 b^{3} and independent of the plastic strain, indicating that the rate controlling mechanism is thermally activated overcoming of the Peierls potential by nucleating a double kink. Dislocation velocity-stress exponent, m^{*}, was also obtained to be 9.0, 6.6 and 6.0 at 292, 350 and 420^{°}K, respectively, from Gupta and Li's analysis of the relaxation data. By using two parameters, V_{0}^{*} and m^{*}, the thermal component of the flow stress, σ^{∗}, could be calculated from the relation of σ^{*}=m^{*}kT/V^{*}. The σ^{*}-T relation showed a good agreement with Friedel's formula, which led to the Peierls stress of τ _{p}^{0}=58 kg/mm^{2}.

(Received 1975/11/17)

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