純銅の低温塑性疲労挙動に及ぼす結晶粒度の影響

概要

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Pure copper wires with grain size of 7.5, 23.5, and 123.0 μm were cyclically strained in torsion with constant strain amplitudes of 0.025 and 0.05 at 77 K. The effect of grain size on the behavior of lattice defects was studied by measuring the change in resistivity during fatigue as a function of r of number of cycles at 77 K. The dislocation density in a fatigued specimem is given by ρ^<1/2>=(α')/(β')(1-e^<-(β'/γ)2>) β'=β+(K_3)/(Δγ), β=a+b/d where ρ is the dislocation density, α' and K_3 are constants depending on the grain size of the specimen, γ is the cumulative plastic strain, Δγ is the plastic strain amplitude, d is the grain size, and a and b are constants. The increase in dislocation density was much smaller in the coarser size specimen during cyclic straining, and, therefore, a smaller peak torque was attained in this material. The change in concentration of point defect C_i in the fatigued specimen is represented as follows. [numerical formula] where K_4 and K_5 are constants. The concentration of vacancies determined experimentally by isothermal annealing was in agreement with the result calculated from the above equation.
1982-03-15