Left: pure zirconia; middle: zirconia/metal composite; right: pure metal
Additive manufacturing has rapidly become more advanced than it used to be, moving far beyond the days when components could only be 3D printed out of a single plastic or metal material. Now other materials, such as ceramics, can be 3D printed as well. Ceramics 3D printing has progressed quickly in the past few years, and ceramic materials with different properties can now be combined. A paper entitled “Hybridization of Materials and Processes by Additive Manufacturing” takes a look at the 3D printing of ceramics with different colors or pore structures, and even ceramics with stainless steel added.
In the study, the researchers chose two feedstock-based 3D printing methods for combining either porous and dense ceramic components, black and white zirconia or stainless steel and zirconia. For the first method, FFF 3D printing, a dual-nozzle 3D printer was used; the first print head was loaded with zirconia filament and the second was loaded with a 17-4PH stainless steel filament. The same parameters were used to print both materials, though the print head temperatures differed slightly.
Cuboid samples were 3D printed, alternating the materials every two or three layers. The samples were then debinded and sintered, leading to dense, well-bonded parts.
In another procedure, the researchers used thermoplastic 3D printing, which combines the advantages of FFF, robocasting and inkjet printing, using a dropwise deposition of a viscous thermoplastic material for building a ceramic component. This method has a number of advantages, including the following:
- There are almost no restrictions concerning the applied powder material, because the consolidation of the droplets occurs by increasing the viscosity during cooling
- Composite or multi-material objects can be printed by using two or more printing heads
- By using a pure thermoplastic binder in one print head, support structures can be built up in parallel to the component
- Completely dense ceramic components can be produced thanks to the high packing density in the green component
- Small droplets enable a high resolution in critical volumes
- Precise deposition of small droplets can be combined with fast jetting of molten suspensions
For their experiments the researchers prepared zirconia suspensions using nanoscale zirconia powder. To produce black and white components, another suspension was prepared using a TZ-Black powder. As a binder system, a mixture of paraffin and beeswax was used.
“The binder system and a dispersing agent were heated up to 100 °C and homogenized for 30 min in a heatable dissolver,” the researchers explain. “Then powder and if necessary pore forming agents (PFA) like polysaccharide were added and the suspensions were homogenized by stirring for 2 h at 100 °C.”
The samples were printed, debinded and sintered. After sintering, nearly dense and porous volumes were combined in one component. To illustrate the different porosities, the samples were placed in front of a light, with the more porous sections appearing darker. Both approaches, FFF and thermoplastic 3D printing, allowed the researchers to create components with varied properties, whether that be material, porosity or color.
Authors of the paper include Tassilo Moritz, Uwe Scheithauer, Steven Weingarten, Johannes Abel, Robert Johne, Alexander Michaelis, Stefan Hampel and Santiago Cano Cano.
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