Ultrasonic-Induced Phase Redistribution and Acoustic Hardening for Rotary Ultrasonic Roller Burnished Ti-6Al-4V
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ULTRASOUND was first applied to the metal forming in 1955.[1] Blaha and Langenecker investigated the ultrasonic effect on the deformation behavior of zinc crystal. Then, Langenecker performed a series of experiments to analyze the effect of ultrasonic stress wave on the physical properties of zinc and copper in 1962.[2,3] The experimental results demonstrated that low-amplitude ultrasonic waves left no residual effects on the physical properties of metals when acoustic irradiation was stopped. However, the critical ultrasonic powers for zinc and copper were found. When the superimposed ultrasonic power exceeded the threshold, the permanent influences on the physical properties would be reserved in the material, such as hardness and yield strength.
JIAN ZHAO, ZHANQIANG LIU, LUANXIA CHEN, and YANG HUA are with the School of Mechanical Engineering, Shandong University, Jinan 250061, China and also with the Key Laboratory of High Efficiency and Clean Mechanical Manufacture of MOE/Key National Demonstration Center for Experimental Mechanical Engineering Education, Jinan 250061, Shandong University, China. Contact e-mail: [email protected] Manuscript submitted July 12, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
The hardening effects caused by ultrasonic vibration are called acoustic hardening. The performances of acoustic hardening are presented as below: the increment of yield stress, the increasing of surface hardness and the introduction of deeper compressive residual stress. Many researchers explored the acoustic hardening mechanism in various ultrasonic-assisted machining processes such as ultrasonic grinding,[4] ultrasonic drawing,[5] ultrasonic cutting,[6] ultrasonic forming[7] and ultrasonic burnishing.[8–12] However, the acoustic hardening effects are different for various materials. Yao[13] researched the plastic behavior of aluminum by ultrasonic upsetting. The flow stress of aluminum increased after ultrasonic vibration was turned off. However, the flow stress of AZ31 magnesium alloy didn’t exceed the normal level by switching off the ultrasonic vibration.[14] Liu et al.[15] conducted the compression experiment of pure titanium with the assistance of ultrasonic vibration. Results showed that the flow stress of pure titanium decreased with the increment of ultrasonic amplitude. The flow stress of pure titanium in ultrasonic-assisted compression was lower than its normal flow stress in conventional compression. When ultrasonic vibration was stopped, the flow stress of pure titanium presented a sudden jump, but it was still lower than the normal flow stress.
Ti-6Al-4V is one of most widely used titanium alloys. However, it is a typical difficult-to-machine material with large chemical activity and low elastic modulus.[16] The traditional machining technology, such as turning and milling, would suffer the high-machining cost. Hot-forming processing also affects the microstructure and mechanical properties of Ti-6Al-4V. However, how to control processing temperature precisely is still a critical problem. Ti-6Al-4V alloys wit
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