Researchers from the City University of Hong Kong (CityU) are taking ceramic additive manufacturing to new heights with the development of the world’s first 4D printing process for ceramics. The breakthrough process—still in its research stage—is capable of creating strong and incredibly complex ceramic structures.
4D printing, as most in the AM industry will know, adds the fourth dimension of time into the 3D printing equation by way of creating structures which change, self-assemble or shape-shift when exposed to external forces such as light, temperature, humidity or magnetism. Presently, most applications for 4D printing are limited to research, though there are some truly innovative and interesting projects being developed.
At Rutgers University, for instance, engineers have created a 4D printing method for creating shape-shifting smart gel structures, while MIT engineers recently unveiled soft, 3D printed structures which can be controlled using magnets. The project undertaken by CityU and led by Professor Lu Jian, however, is the first time we’ve seen ceramics and 4D printing combined. And for good reason.
Ceramics, a quickly advancing subsection of the AM industry, have a high melting point making them hard to work with using laser-based printing methods. 3D printable ceramic precursors, for their part, can be difficult to deform which impedes the production of complex ceramics. In light of these challenges, the CityU researchers developed a ceramic ink made from a mixture of polymers and ceramic nanoparticles.
These nanoparticles of ceramic precursors are notable for the soft and stretchable properties. As the research team explains, the ceramic precursors can be stretched to three times beyond their initial length which enables the fabrication of complex shapes, including origami-like folding structures.
The CityU researchers leveraged the elastic energy in the stretch precursors to enable shape morphing. More specifically, when the stretched ceramic precursors are released from their stretched state, they automatically reshape. Then, once the object has undergone heat treatment, the ceramic precursors become hard, mechanically robust ceramics. According to the research team, these ceramics have demonstrated high compressive strength-to-density ratios (547 MPa on 1.6 g cm-3 microlattice) and can be made into larger structures than other printed ceramics.
“The whole process sounds simple, but it’s not,” elaborated Professor Lu, the Vice President and Chair Professor of Mechanical Engineering at CityU. “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.”
Indeed, the 4D printed ceramics have been a longtime in the making, as it has taken the research team over 2.5 years to overcome challenges and present the ceramic 4D printing process. A study on the project, recently published in the journal Science Advances, describes the various stages of the research.
In the first shaping method, the researchers 3D printed a ceramic precursor and substrate using the ceramic ink. The substrate was then stretched using a biaxial stretching device and joints for connecting the precursor were 3D printed onto it. With the joints in place, the precursor was applied to the stretched substrate. When the latter was released, the materials morphed into the predesigned shape in a controlled manner. In the second method described by the researchers, the designed pattern was printed directly onto the stretched ceramic precursor. This structure was then released and self-morphed while being controlled by computer programming.
“With the versatile shape-morphing capability of the printed ceramic precursors, its application can be huge!” – Professor Lu.
In terms of applications, the 4D printed ceramics could be particularly useful in the fabrication of electronic devices. Because ceramics showcase better transmission performance for electromagnetic signals than metals, they are increasingly being explored for electronic applications. The researchers add that the 4D printed ceramics could also be used by customers to create bespoke and complexly designed mobile phone back plates.
Outside of electronics, the 4D printed ceramics could also be used in the aerospace industry. “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,” explained Prof Lu.
Still, there is some work left before the 4D printed ceramic parts are commercially viable. The next step in the research effort, according to Prof Lu, will be to improve the mechanical properties of the ceramic ink and to reduce brittleness.
To learn more about existing ceramic additive manufacturing technologies, check out our Complete Ceramics 3D Printing Guide.