Cornell University engineers have developed a new technology for 3D printing metal objects – it involves jetting titanium particles at supersonic speed. The resulting metals are highly porous, which makes them particularly useful for biomedical objects such as implants and replacement joints.
Traditional 3D printing involves a nozzle that deposits plastic, hydrogel, living cells, or other materials layer by layer to build an object. Metal parts and objects are usually 3D printed in other ways, such as launching a laser onto a bed of metal powder to selectively melt parts into a desired shape, or launching metal powder onto a substrate at high speed to fuse the particles together .
The latter method is called "cold spray", and the new technology has been expanded on this basis. The Cornell University team sprayed titanium alloy particles at a speed of 600 meters per second, each with a width between 45 and 106 microns. The team calculated that this is the ideal speed-no matter how fast it is, the particles will disintegrate upon impact and cannot be combined with each other.
Next, the material is heated to soften and help the particles better bond. Again, this is carefully controlled, using temperatures up to 900 °C, which is much lower than the melting point of titanium of 1626 °C. The end result is a metal object with a porous structure that is 42% stronger than similar objects made using traditional manufacturing processes. The team said that the difference is that the new method does not focus on high heat as the main force, because high heat can bring weakness to the material.
"We focus on making porous structures, which have many applications in thermal management, energy absorption, and biomedicine," said Atieh Moridi, the lead author of the study. "We are now not only using heat as the input or the driving force for bonding, but using plastic deformation to bond these powder particles together."
The researchers said that this new method is particularly suitable for creating biomedical implants, because the porous structure allows the patient's cells to attach, helping to rebuild natural tissues and fix the implant.
"If we make an implant with this porous structure and insert it into the body, bone can grow in these pores and be biofixed," Moridi said. "This helps reduce the possibility of implant loosening. And this is a big problem. There are many revision surgeries, and patients have to remove the implants, just because the implants are loose, and it causes a lot of pain of."
The team said that this new method can also create materials and objects for other industries, such as construction, transportation and energy.
The research was published in the journal Applied Materials Today.