Researchers print biomedical parts in 3D at supersonic speed

Forget about glue, screws, heat or other traditional bonding methods. A collaboration led by Cornell University has developed a 3D printing technique that creates cellular metallic materials by crushing powder particles together at supersonic speed.

This form of technology, known as “cold spraying,” results in mechanically strong porous structures that are 40% stronger than similar materials made with conventional manufacturing processes. The small size and porosity of the structures make them particularly well suited for the construction of biomedical components, such as replacement gaskets.

The team’s article, “Solid-State Additive Manufacturing of Porous Ti-6Al-4V by Supersonic Impact”, published on November 9 in Materials applied today.

The main author of the article is Atieh Moridi, Assistant Professor at the Sibley School of Mechanical and Aerospace Engineering.

“We have focused on the fabrication of cellular structures, which have many applications in thermal management, energy absorption and biomedicine,” said Moridi. “Instead of just using heat as the input or as a driving force for the bond, we are now using plastic deformation to bind these powder particles together.”

Moridi’s research group specializes in the creation of high performance metallic materials through additive manufacturing processes. Rather than cutting a geometric shape out of a large block of material, additive manufacturing builds the product layer by layer, a bottom-up approach that gives manufacturers greater flexibility in what they create.

However, additive manufacturing is not without its challenges. First and foremost: Metallic materials must be heated to high temperatures that exceed their melting point, which can cause residual stress buildup, distortion and unwanted phase transformations.

To eliminate these problems, Moridi and colleagues developed a method using a compressed gas nozzle to shoot titanium alloy particles onto a substrate.

“It’s like painting, but things pile up a lot more in 3-D,” Moridi said.

The particles were between 45 and 106 microns in diameter (a micron is a millionth of a meter) and moved at about 600 meters per second, faster than the speed of sound. To put this into perspective, another traditional additive process, direct energy deposition, delivers powders through a nozzle at a speed of around 10 meters per second, making Moridi’s method sixty times faster.

The particles are not just launched as quickly as possible. The researchers had to carefully calibrate the ideal speed of the titanium alloy. In general, in cold spray printing, a particle accelerates in the ideal zone between its critical speed – the speed at which it can form a dense solid – and its erosion rate, when it crumbles too much to bind to anything.

Instead, Moridi’s team used computational fluid dynamics to determine a velocity just below the critical velocity of the titanium alloy particle. When launched at this slightly slower speed, the particles created a more porous structure, ideal for biomedical applications, such as artificial knee or hip joints and cranial / facial implants.

“If we make implants with these kind of porous structures and insert them into the body, bone can grow inside these pores and perform biological fixation,” Moridi said. “It helps reduce the likelihood of the implant coming loose. And that’s a big deal. There are a lot of revision surgeries that patients have to undergo to remove the implant just because it’s loose and because it’s loose. it causes a lot of pain. “

Although the process is technically called a cold spray, it involved heat treatment. After the particles collided and bonded, the researchers heated the metal so that the components diffuse into each other and settle as a homogeneous material.

“We focused only on titanium alloys and biomedical applications, but the applicability of this process could go beyond that,” Moridi said. “Essentially, any metallic material that can withstand plastic deformation could benefit from this process. And it opens up many opportunities for larger scale industrial applications, such as construction, transportation and energy.”