3D printed titanium alloys under an electron microscope: the sample on the left with large, elongated crystals was printed conventionally, while the sample on the right with finer, shorter crystals was printed sitting on an ultrasonic generator. Image: RMIT University.
3D printed titanium alloys under an electron microscope: the sample on the left with large, elongated crystals was printed conventionally, while the sample on the right with finer, shorter crystals was printed sitting on an ultrasonic generator. Image: RMIT University.

Researchers from Australia have used sound vibrations to shake metal alloy grains into tighter formation during 3D printing. In a paper in Nature Communications, the researchers show how 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.

According to Carmelo Todaro, a PhD candidate in RMIT University's School of Engineering, these 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," Todaro explained. "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 that these printed metal parts benefited from a 12% improvement in tensile strength and yield stress compared with those made by conventional additive manufacturing. The team demonstrated their ultrasound approach using two major commercial grade alloys: a titanium alloy known as Ti-6Al-4V, commonly used for aircraft parts and biomechanical implants; and a nickel-based superalloy called Inconel 625, often used in marine and petroleum industries.

By simply switching the ultrasound 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. This could be useful for what's known as functional grading.

Ma Qian, a distinguished professor at RMIT and the project supervisor, said he hoped the team’s 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. 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."

This story is adapted from material from RMIT University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.