## Work Hardening in Molybdenum

Koji Tanoue1, Kenji Senba2 and Kenji Okazaki1

1Department of Metallurgy, Kyushu Institute of Technology, Kitakyushu
2Nippon 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 n1, n2 and h1, while an increase in temperature resulted in the decrease in h2 (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 εn) 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*(T, \dotε)+σ μ _1, where σ μ _1 was estimated to be 5.0 kg/mm2. Subsequently, σ* was calculated to be 23.3, 10.0 and 3.5 kg/mm2 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.