RMIT researchers explore use of ultrasound in 3D printing

A study by RMIT University researchers has shown that sound vibrations can be used to improve the micro-structure of 3D printed alloys.

The researchers found that high frequency sound waves can have a significant impact on the inner micro-structure of 3D printed alloys, making them more consistent and stronger than those printed conventionally.

Carmelo Todaro, the study’s lead author and a PhD candidate from RMIT University’s School of Engineering, said that the results could inspire new forms of additive manufacturing.

“If you look at the microscopic structure of 3D printed alloys, they’re often made up of large and elongated crystals,” said Todaro.

“This can make them less acceptable for engineering applications due to their lower mechanical performance and increased tendency to crack during printing.”

“But the microscopic structure of the alloys we applied ultrasound to during printing looked markedly different. The alloy crystals were very fine and fully equiaxed, meaning they had formed equally in all directions throughout the entire printed metal part.”

Tests found that these parts had a 12 per cent improvement in tensile strength and yield stress compared to those made through conventional additive manufacturing.

The research team’s ultrasound approach was demonstrated using two major commercial grade alloys, a titanium alloy commonly used for aircraft parts and biomechanical implants, known as Ti-6Al-4V, and a nickel-based superalloy often used in marine and petroleum industries called Inconel 625.

By switching the ultrasonic generator on and off during printing, the team also showed how specific parts of a 3D printed object can be made with different microscopic structures and compositions, useful for what’s known as functional grading.

RMIT’s Distinguished Professor Ma Qian, study co-author and project supervisor, said he hoped the results would increase ultrasound devices designed for metal 3D printing.

“Although we used a titanium alloy and a nickel-based superalloy, we expect that the method can be applicable to other commercial metals, such as stainless steels, aluminium alloys and cobalt alloys,” Qian said.

“We anticipate this technique can be scaled up to enable 3D printing of most industrially relevant metal alloys for higher‑performance structural parts or structurally graded alloys.”