An ultrasonic surgical instrument is disclosed including an ultrasonic transducer, an ultrasonic end effector comprising a proximal end formed of a first material having a first coefficient of thermal expansion, and a waveguide configured to transmit ultrasonic energy generated by the ultrasonic transducer to the ultrasonic end effector. The waveguide includes an attachment portion formed of a second material having a second coefficient of thermal expansion that is greater than the first coefficient of thermal expansion. The attachment portion is configured to be selectively expandable into an acoustically coupled retaining engagement with the ultrasonic end effector by expanding faster than the proximal end of the ultrasonic end effector when heat is applied to establish an interference fit therebetween.