Stronger 3D-printed alloys with ultrasound: research

A study by researchers at RMIT shows high-frequency soundwaves can have a significant impact on the inner microstructure of 3D-printed alloys, making them more consistent and stronger than those printed conventionally.

Lead author Carmelo Todaro, a PhD candidate from RMIT University’s School of Engineering, said the promising 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,” he said. “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.”

Testing showed these parts were also stronger: they had a 12% improvement in tensile strength and yield stress compared to those made through conventional additive manufacturing.

The team demonstrated their ultrasound approach 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.

Left: Large, elongated crystals printed conventionally. Right: Finer, shorter crystals printed while sitting on a ultrasonic generator.

By simply 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 promising results would spark interest in specially designed ultrasound devices 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,” said Qian. “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.”

The study has been published in Nature Communications.

Top image: Carmelo Todaro and Ma Qian inspect a 3D-printed titanium alloy cube on the tip of an ultrasound rod.