抄録
The thermal component of the flow stress in MARZ zone-refined titanium is directly evaluated from the single strain-rate cycling tests and the athermal component directly from the double strain-rate cycling tests over the temperature range of 77 to 500°K and some grain sizes. These thermal and athermal components are in good accord with those obtained from the conventional extrapolation method, proving its validity in the wide range of temperature. It is concluded that the single strain-rate cycling method is a quite effective method not only for evaluating the thermal component directly in the wide temperature range but also for providing the parameters necessary to the thermal activation analysis of deformation. The strain rate-stress exponent, m increases with increasing plastic strain and with decreasing grain size and temperature. The dislocation velocity-stress exponent, m*, decreases with increasing temperature, while m*T remains constant. Deformation dynamics analysis of the experimental data obtained from the various methods used in the present work yields to the thermal component τ0*=15 kg/mm2 at 0°K, the activation volume for the plastic flow of MARZ titanium, VT′0*=64b3 and the activation enthalpy H0=1.25 eV(0.21 μ b3) at 540°K where the applied stress becomes insensitive to temperature, and a linear force-distance curve with FM=42×10−6 dynes (0.09 μ b2) and X0=1.6b. These parameters are in good accord with the thermally activated overcoming of interstitial atoms as the rate controlling mechanism in MARZ titanium.
