Researchers from Australia’s Royal Melbourne Institute of Technology (RMIT) University School of Engineering have used ultrasonic sound waves to strengthen the properties of 3D printed alloys.
A study published today in Nature Communications has demonstrated how high-frequency sound waves can have a significant impact on the inner microstructure of 3D printed alloys. They can cause the alloy grains to maintain a tighter formation during the 3D printing process, consequently making them stronger than alloys 3D printed through conventional means.
Lead author and Ph.D. candidate from RMIT University’s School of Engineering, Carmelo Todaro, explains how the results can lead to new processes in 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.”
Strengthening 3D printed alloys with high frequency sound
To demonstrate their ultrasound approach, the research team used two major commercial grade alloys: Ti-6Al-4V titanium alloy, and nickel-based superalloy Inconel 625. Whereas the former is often used for aircraft parts and biomechanical implants, the latter is commonly applied in the marine and petroleum industries.
The team tested the 3D printed parts by comparing the tensile strength of the components when 3D printed conventionally to the parts after being processed through their ultrasound approach. Using ultrasound, the 3D printed parts showed a 12 percent improvement in tensile strength and yield stress over the standard additive manufacturing process.
Additionally, the ultrasound generator can be turned on and off during the 3D printing process, allowing specific parts of a 3D printed object to be constructed with different microscopic structures and compositions. Such a technique can prove useful in producing functionally graded material.
Study co-author and project supervisor, RMIT’s Distinguished Professor Ma Qian, hopes that the results will inspire further research 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,” commented 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.”
Metal 3D printing research at RMIT
RMIT continues to push the boundaries of metal 3D printing through its consistent research output surrounding the process. In late 2019, the university shared details of a new material it trialled for metal 3D printing. The material in question is a combination of titanium alloy with copper. It was created in a bid to prevent cracking and distortion that can affect titanium when 3D printing. RMIT states that the material can potentially lead to a new range of high-performance alloys for medical device and aerospace applications.
Additionally, a PhD candidate at RMIT won a $15 thousand AUD ($10 thousand USD) prize for proving the 3D printability of tool steel in February last year. RMIT has also led a project seeking to apply metal 3D printing to service the Australian Defence Forces.
Researchers at RMIT are not the first to have experimented with sound waves in the 3D printing process, however. At Harvard University’s John A Paulsen School of Engineering and Applied Sciences (SEAS), researchers had previously created an acoustophoretic 3D printing technique which uses sound waves to form drops of a wide range of viscous fluids into additively manufactured structures.
RMIT’s study, ‘Grain structure control during metal 3D printing by high-intensity ultrasound’ is published in Nature Communications with DOI: 10.1038/s41467-019-13874-z. The research was conducted at RMIT University’s Advanced Manufacturing Precinct and supported by an Australian Research Council Discovery Project grant.
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Featured image shows Carmelo Todaro and Ma Qian inspecting a 3D printed Titanium alloy cube on the tip of an ultrasound rod. Photo via RMIT.
