Aug 20, 2018 | By Thomas

Until now, it has been difficult to apply conventional laser 3D printing techniques to ceramic because of its high melting point. The existing 3D printed ceramic precursors, which are usually difficult to deform, also hinder the production of ceramics with complex shapes.

Printed ceramic origami mimicking the Sydney Opera House. Credit: City University of Hong Kong

A research team at City University of Hong Kong (CityU) overcame these challenges and has successfully developed the world's first-ever 4D printing method for ceramics, which are mechanically robust and can have complex shapes.

4D printing is conventional 3D printing combined with the additional element of time as the fourth dimension, where the printed objects can re-shape or self-assemble themselves over time with external stimuli, such as mechanical force, temperature, or a magnetic field.

In order to achieve their desired effects, the CityU team developed a novel "ceramic ink," which is a mixture of elastic polymers (dimethylsiloxane) and ceramic nanoparticles (Crystalline ZrO2 NPs with a primary average size of 20 to 50 nm in diameter). When heat is applied, the 3D-printed ceramic precursors printed with this novel ink can be stretched three times greater than their starting length. These flexible and stretchable ceramic precursors also allow origami folding, as well as the creation of more complex shapes.

4D-printed ceramic Miura-ori. Credit: City University of Hong Kong

In this research, the team made use of the elastic energy stored in the stretched precursors for shape morphing. When the stretched ceramic precursors are released, they undergo self-reshaping. After heat treatment, the precursors turn into ceramics.

The resultant elastomer-derived ceramics are mechanically robust. They can have a high compressive strength-to-density ratio (547 MPa on 1.6 g cm-3 microlattice), and they can come in large sizes with high strength compared to other 3D printed ceramics.

The innovative two-step process took two years to develop. "The whole process sounds simple, but it's not," said Professor Lu Jian, Vice-President (Research and Technology) and Chair Professor of Mechanical Engineering who led the research. "From making the ink to developing the printing system, we tried many times and different methods. Like squeezing icing on a cake, there are a lot of factors that can affect the outcome, ranging from the type of cream and the size of the nozzle, to the speed and force of squeezing, and the temperature."

Origami and 4D printing of EDCs via DIW–morphing–heat treatment method.
(A) 3D-printed elastomeric lattices for origami. (B) Optical image of DIW of inks. (C) Origami of ceramic structures derived from 3D-printed elastomers. (D and E) Two 4D printing methods, including method 1 (D) and method 2 (E), together with heat treatment, convert 3D-printed elastomer into 4D-printed ceramics. Examples: (F) Flat (left) and curved (right) cellphone back plate. (G) Top view of 3D-printed flat cellphone back plate. (H) Curved ceramic honeycomb. The inset indicates the curvature of the honeycomb. Scale bars, 1 cm.

The research team developed two methods of 4D printing of ceramics. In the first shaping method, two forms, a 3D-printed ceramic precursor and substrate, were first printed with the new ink. The substrate was stretched using a biaxial stretching device, and joints for connecting the precursor were printed on it. The precursor was then placed onto the stretched substrate. With the computer-programmed control of time and the release of the stretched substrate, the materials morphed into the desired shape.

In the second method, the designed pattern was directly printed on the stretched ceramic precursor. It was then released under computer control to morph into the final form.

Professor Lu believes that electronic devices will be an promising application sector for this technology. Ceramics have much better performance in transmitting electromagnetic signals than metals, and they are expected to play a much more important role in the manufacture of electronic products such as tailor-make ceramic mobile phone back plates when 5G networks come into use.

Furthermore, this innovation can be applied in the aero industry and space exploration. "Since ceramic is a mechanically robust material that can tolerate high temperatures, the 4D-printed ceramic has high potential to be used as a propulsion component in the aerospace field," said Prof Lu.

Prof Lu said the next step is to enhance the mechanical properties of the material, in particular by reducing its brittleness.

The innovative work was published in the Advanced Sciences journal this week under the title "Origami and 4D printing of elastomer-derived ceramic structures."



Posted in 3D Printing Technology



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