As you may know, 3D printing can be used to create medical implants. However, there is still room for improvement. That is why a team of researchers from MIT, Cornell University, and more have explored a new method of 3D printing. Ti64 powder, which might be available at a 3D printing service as well, has been used for this experiment. Besides that, they also used a cold spraying technique. This operates at a temperature way below that of titanium’s melting point. Instead, it deploys kinetic energy as the primary energy source. Because of this, the metal powder can be deposited at supersonic speeds to create solid-state bonding and porous structures. This results in improved mechanical properties and biocompatibility with bone enveloping preosteoblast cells.
High-temperature 3D printing limitations
Most 3D printing processes utilize a laser to melt successive layers of material on top of each other. This does work, but the high-temperature can have bad effects on the result. Parts made via powder bed fusion usually struggle with large residual stresses for example. The cyclic cooling and heating caused by a scanning laser can also generate shear stresses within a 3D printed piece. These residual stresses can actually destroy the product in extreme scenarios. Cold spraying has been developed to avoid problems related to heat. Instead, it accelerates powder particles to supersonic impact velocities of around 600 m/s out of a de Laval nozzle. The jetted material should have just enough kinetic energy to fuse with the substrate. With Ti64 the cold spraying happens at around 800 to 900 degrees Celsius, while the material’s melting point is much higher.
Cold spraying Ti64
In order to test the technique with titanium alloy, the researchers simply conducted a few basic deposition studies with the material. This resulted in them finding that it was possible to spatially control the porosity of the deposits with modifications to the powder impact velocity. They achieved a maximum porosity of 30 percent. Another result was that cold spraying Ti64 could result in better mechanical properties than when a laser-based 3D printing method was used. The team determined an apparent compressive yield strength of 535MPa. This is reportedly 42 percent higher than high-temperature DED. On top of that, it was proven that the cold sprayed Ti64 was to be biocompatible with MC3T3-E1 SC4 murine preosteoblast cells.
