Engineers at Cornell University have developed a new technique for 3D printing metallic objects – and it involves blasting titanium particles at supersonic speeds. The resulting metals are very porous, which makes them particularly useful for biomedical objects like implants and replacement joints.
Traditional 3D printing involves a nozzle depositing plastic, hydrogels, living cells or other materials layer by layer to build up an object. Metal parts and objects are usually 3D printed in other ways, such as firing a laser at a bed of metal powder to selectively melt sections into the desired shape, or firing metal powder at high speeds at a substrate to fuse the particles together.
The latter method is known as “cold spray,” and the new technique expands on that base. The Cornell team blasted titanium alloy particles, each measuring between 45 and 106 microns wide, at speeds up to 600 m (1,969 ft) per second (for reference, the speed of sound in air is around 340 m (1,115 ft) per second). The team calculated this as the ideal speed – any faster, and the particles would disintegrate too much on impact to bond to each other.
Next the materials are heated to soften them, helping the particles bond better. Again this is carefully controlled, using temperatures of up to 900 °C (1,652 °F), which is well below titanium’s melting point of 1,626 °C (2,959 °F).
The end result is a metallic object with a porous structure that can be up to 42 percent stronger than similar objects made using conventional manufacturing processes. The difference, the team says, is that the new method doesn’t focus on high heat as the primary force, which can introduce weaknesses to the material.
“We focused on making cellular structures, which have lots of applications in thermal management, energy absorption and biomedicine,” says Atieh Moridi, lead author of the study. “Instead of using only heat as the input or the driving force for bonding, we are now using plastic deformation to bond these powder particles together.”
The researchers say the new method is particularly well-suited to creating biomedical implants because the porous structure would give patients' cells somewhere to cling to, helping rebuild the natural tissue and anchor the implant.
“If we make implants with these kind of porous structures, and we insert them in the body, the bone can grow inside these pores and make a biological fixation,” says Moridi. “This helps reduce the likelihood of the implant loosening. And this is a big deal. There are lots of revision surgeries that patients have to go through to remove the implant just because it’s loose and it causes a lot of pain.”
The team says that the new method could also create materials and objects for other industries, such as construction, transportation and energy.
The research was published in the journal Applied Materials Today.
Source: Cornell University
