Takao Endo1, Toshio Nomura2, Toshio Enjyo1 and Masao Adachi1
1Department of Metal Science and Technology, Fuculty of Engineering, Kyoto University, Kyoto
The flow stress and strain rate sensitivity of Al-Zn solid solution alloys were measured in the range of temperature from 400° to 550°C and of strain rate from 10-5 to 10-2/sec. When the strain exceeds about 10%, the deformation proceeds at a constant stress until the onset of necking. This type of steady state creep deformation is expressed in the form of ε·s = A σn exp (-Q/kT), where ε·s is the steady state creep rate, σ the applied stress, n the stress exponent (∼4.5), Q the apparent activation energy for creep (∼1.57 eV). The increment in short-range stress with a dislocation velocity change was measured by a strain rate change during the steady state creep. The results of strain rate sensitivity measurements indicate that the dislocation velocity varies as a power of effective stress. The ratio of short-range stress to creep stress was estimated at about 0.3 from the strain rate sensitivity. These results favour that the rate controlling mechanism of the creep deformation is a non-conservative motion of screw dislocations with a large number of intersection jog.
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