High power ultrasonic vibration is widely used for improving manufacturing processes such as machining and metal forming. High frequency mechanical vibration affects material properties and friction forces in contacting surfaces. Flow stress reduction under superimposed ultrasonic vibration is called as acoustic softening. The amount of this parameter should be determined for ultrasonic assisted metal forming processes. For determination of this parameter for workhorse Ti-6Al-4V alloy, experimental setup was designed and fabricated. Then tensile test under longitudinal ultrasonic vibration was performed for different ultrasonic powers. Results show that ultrasonic vibration has considerable effect on plastic behavior of the alloy and decreases flow stress. Also, increasing ultrasonic power leads to higher acoustic softening. Yield stress reduction up to 9.52%, ultimate stress reduction up to 4.55% and elongation up to 13% were obtained at 340W ultrasonic power. After applying ultrasonic vibrations and its termination, hardness of specimens were measured in which increase up to 9% was observed.

Titanium has widely been used in chemical and aerospace industries. In order to overcome the drawbacks of cold compaction of titanium, the process was assisted by an ultrasonic vibration system. For this purpose, a uniaxial ultrasonic assisted cold powder compaction system was designed and fabricated. The process variables were powder size, compaction pressure and initial powder compact thickness. Density, friction force, ejection force and spring back of the fabricated samples were measured and studied. The density was observed to improve under the action of ultrasonic vibration. Fine size powders showed better results of consolidation while using ultrasonic vibration. Under the ultrasonic action, it is thought that the friction forces between the die walls and the particles and those friction forces among the powder particles are reduced. Spring back and ejection force didn't considerably change when using ultrasonic vibration.

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In this study, longitudinal ultrasonic vibration was superimposed during the compaction of titanium powders. Then, specimens were vacuum sintered at 1273 K for 120 min. In order to investigate vibration influence on physical/mechanical properties, density, shrinkage, and compression strength of sintered samples were measured. The influence of powder size, compaction pressure, and aspect ratio also were studied on mentioned physical properties. Improvement of fine powder sintered samples density due to applied ultrasonic is greater than coarse powders, although their compacted density is lower than coarse powders samples. Dimensional stability (in the opposite of shrinkage) in coarse powder is greater than fine powders so that shrinkage in fine powders decreases up to 12%. Compression strength is improved due to the application of ultrasonic vibration up to 64%.