Effects of superimposed ultrasound on deformation of gold

The effects of superimposed ultrasound vibration on plastic deformation of gold are studied both during and after the vibration using an ultrasonic ball bonding machine. It is found that when ultrasonic irradiation is applied along with mechanical force, the metal is softer than when deformed without the vibration. After ultrasound is turned off, the deformed metal remains softer if previously deformed with ultrasound. Possible mechanisms for the acoustic residual softening are discussed as compared to residual hardening. The acoustic residual effect is attributed to the net balance between ultrasound’s dynamic annealing and its potential opposing effect on activating and multiplying dislocations.