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J. Japan Inst. Metals, Vol. 40, No. 11 (1976),

pp. 1140-1144

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Work Hardening 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:

Stress-strain curves of sintered pure molybdenum were analyzed by the Crussard and Jaoul method that assumes the Ludwik equation, σ=σ _{0}+h ε ^{n}. Also, the effects of temperature (292∼550^{°}K) and stain rate (10^{-6}∼10^{-2} sec^{-1}) on the constants h and n were studied. Obviously, the Crussard and Jaoul plot exhibited a ``double-n behavior''. Both temperature and strain rate had no influence upon the parameters n_{1}, n_{2} and h_{1}, while an increase in temperature resulted in the decrease in h_{2} (h at ε>ε _{1}) and ε _{1}, the latter being independent of strain rate. The double-n behavior was discussed with the aid of a dislocation model reported by Bergstr\"om, and it was concluded that ε _{1} did not correspond necessarily to the plastic strain for the formation of cell structures.

σ _{0} (=σ-h ε^{n}) was independent of the plastic strain, but varied strongly with temperature and strain rate. Again, σ _{0} could be divided into two components, i.e. σ _{0}=σ^{*}(T, \dotε)+σ _{μ _1}, where σ _{μ _1} was estimated to be 5.0 kg/mm^{2}. Subsequently, σ^{*} was calculated to be 23.3, 10.0 and 3.5 kg/mm^{2} at 292, 350 and 420^{°}K, respectively for \dotε=3.3×10^{-4} sec^{-1}, and they are in a good agreement with the previous results from stress relaxation tests. Finally, log σ^{*} versus log \dotε plots showed a good linear relation, and the dislocation velocity-stress exponent, m^{*} (=_{d} ln \dotε/_{d} ln σ^{*}) was deduced to be 6.5 independent of test temperatures above 292^{°}K.

(Received 1976/03/15)

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