Evaluation of microplastic flow stress in copper alloys from amplitude-dependent internal friction

Stress-strain relations are evaluated from amplitude-dependent internal fri ction in polycrystalline solid solution copper alloys. The Row stress in mi croplastic strain range much below the yield point is examined for eight ki nds of specimens, prepared by alloying commercial-grade pure copper with 0. 3 at% solute atoms (aluminum, silicon, nickel, gallium, germanium, indium, tin and gold). Internal friction is measured at room temperature under atmo spheric pressure using the free-decay method of flexural resonant vibration with both free ends around 600 Hz. The Row stress of Cu-Sn alloys required to cause the plastic strain of 1 x 10(-9) is about 440 times larger than t hat of pure Cu, while that of Cu-Ni alloys only 6 times larger. Thus the ho w stress evaluated from amplitude-dependent internal friction reflects sens itively the change of solute elements. The Row stress is examined in terms of the misfit parameters between solute and solvent atoms proposed by Fleis cher, and it is shown that the flow stress in microplastic strain range is controlled by the elastic interactions between screw dislocations and solut e atoms in solid solution copper alloys.