3D Printing

Ultrasound found to increase the strength of 3D-printed metal

Ultrasound found to increase t...
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
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
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Researchers Carmelo Todaro and Ma Qian inspect a 3D-printed titanium alloy cube
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Researchers Carmelo Todaro and Ma Qian inspect a 3D-printed titanium alloy cube
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
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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

The quality of 3D-printed metal parts could soon improve, thanks to new research out of Australia. Scientists there have determined that the application of ultrasound boosts the strength of such items, by modifying their microstructure.

Led by PhD candidate Carmelo Todaro, a team at RMIT University experimented with an existing type of 3D printing known as "directed energy deposition" (DED). In a nutshell, this involves using a laser to melt metal powder as it's being deposited onto a surface, one successive layer at a time. That molten metal subsequently solidifies, forming the finished product.

The RMIT researchers printed sample objects out of two different commonly-utilized alloys: Ti-6Al-4V, which is a titanium alloy frequently used for aircraft parts and biomechanical implants; and Inconel 625, a nickel-based superalloy often used in the marine and petroleum industries.

In both cases, the deposition surface was in fact a sonotrode, which is a tool that produces ultrasonic vibrations. These vibrations were applied as the metal was solidifying, essentially shaking the microscopic crystals that made up its grain, so that they formed into a tighter configuration. As a result, the objects were found to have a 12-percent increase in tensile strength and yield stress, as compared to identical samples that were printed without the ultrasound.

Researchers Carmelo Todaro and Ma Qian inspect a 3D-printed titanium alloy cube
Researchers Carmelo Todaro and Ma Qian inspect a 3D-printed titanium alloy cube

"If you look at the microscopic structure of 3D-printed alloys, they're often made up of large and elongated crystals," says 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."

On the other hand, by turning the sonotrode on and off during the printing process, it was also possible to create single items that had different microstructures in different areas. This is a quality known as "functional grading," and it's useful in objects where factors such as low weight or reduced material usage are considerations.

It is believed that once the ultrasound-augmented 3D-printing technology is developed further, it might additionally be used to boost the strength of other metals – these could include stainless steels, along with aluminum and cobalt alloys.

A paper on the research was recently published in the journal Nature Communications.

Source: RMIT via EurekAlert

2 comments
Expanded Viewpoint
How about if they modulate the power of the laser beam with GHz freqs? If they did that with a CO2 or excimer laser beam, it might yield some interesting results!
Robert Schreib
??? Could playing with the TEMPERATURE of the metallic powder change the 3D printed artifact's structural strength as well? What if we put the metal alloy powder used in this example, in a container inside of a copper box, placed in liquid Nitrogen for a long time, before using it to make 3D printed metal products? Also, there was an episode of the CBS-TV show titled "CSI: Cyber", where the heroes were driving a powerful, booby-trapped time bomb in a huge car, and they couldn't figure out how to disarm its rigged wiring! But, they kept it from exploding, by wiring the bomb's battery, to their powerful car's electric system, and the amplified grounding, sucked all of the bomb's battery's juice out, so the bomb could not explode. ANYWAY, when they make metal artifacts by 3D printing, they pass a direct current electric charge, through the molten metal, passing through the ceramic inkjets, that is GROUNDED underneath the artifact being made, to make the assembly more effective. BUT, if we use something like a massive electrical generator, to make a VERY AMPLIFIED grounding effect, could that improve this 3D printing of metal artifacts as well?