Ceramic parts have corrosion resistance and wear resistance, and have excellent high temperature performance, so they are very suitable for propulsion and energy generation systems, as well as chemical processing equipment and medical implants. However, these applications are limited by the difficulty of forming ceramic materials. 3D printing technology can solve this difficulty to a certain extent.
In 2016, the HRL laboratory published in the top issue of "Science" a technology of curing 3D printed ceramics by ultraviolet light—"precursor conversion polymer" technology. The ceramics made by these polymers shrink uniformly. , Almost no porosity.
According to market observations from 3D Science Valley, following this research, the HRL team used this type of ceramic 3D printing technology to manufacture inert particle-reinforced siloxane-based ceramic precursor resin materials, and then 3D printed ceramics through the extreme heating process of pyrolysis The enhanced precursor material is transformed into a carbon silicon oxide (SiOC) composite material. Related research papers were published in the recent Journal of the American Ceramic Society.
Fracture resistant ceramic composite 3D printed parts.
Improve the freedom of ceramic composite manufacturing
In the ceramic component manufacturing method adopted by the HRL laboratory, it is first necessary to use SLA or DLP 3D printers based on the light curing process to manufacture siloxane-based resins. After high temperature (700°C-1100°C) pyrolysis cycles, polymerization The 3D printed parts are directly converted to silicon oxycarbide (SiOC) ceramics. This method eliminates the lengthy debinding step and subsequent sintering step.
HRL has determined the most durable ceramic matrix composite processing range.
HRL 3D printed ceramic composite nozzle.
Challenges of 3D printing ceramic technology
The HRL laboratory pointed out in a recent research paper that the main consideration for all additive manufacturing-3D printing processes is whether the low inherent toughness of ceramics will limit defects such as porosity, lack of fusion, interlayer adhesion, and surface roughness. Tolerance, because these defects will structurally damage the final ceramic parts. If the toughness of 3D printing ceramic materials can be improved, 3D printing ceramic technology may affect many ceramic applications, including propulsion, energy generation, chemical processing, tribology, and ceramic parts used in medical implants.
There are currently ceramic-based reinforced materials. The most famous example is the ceramic-based composite (CMC) using long ceramic fiber reinforced materials, such as silicon carbide/silicon carbide (SiC / SiC), which has a toughness of >30 MPa m1/2. Traditionally, these ceramic matrix composites are made of rigid fiber preforms that have undergone multiple steps of infiltration and pyrolysis of the ceramic precursor polymer.
But the long fiber form factor is not compatible with current commercial 3D printing printers. Short fibers (such as whiskers) and particles with a small aspect ratio can also make the material tougher. For example, using SiC whisker-reinforced alumina (Al2O3) composites, the strain energy absorbed by the bridge cracks improves the toughness of the matrix material> 6 MPa m1/2, particle inclusions deflect the crack tip, and it is possible to increase the shape factor of the whiskers and particles and make them compatible with a variety of additive manufacturing methods. Particle inclusions will deflect the crack tip, possibly increasing toughness by a factor of two. The form factors of the whiskers and particles also make them compatible with a variety of additive manufacturing methods.
Research on ceramic precursor polymers has resulted in the synthesis of a variety of polymers, such as SiOC, silicon carbonitride (SiCN), silicon-based ceramics including SiC and silicon nitride (Si3N4). In the process of converting the ceramic precursor polymer through pyrolysis, the release of volatile substances leads to mass reduction and densification caused by shrinkage. Since volatiles must diffuse through the matrix to escape from the free surface, temperature distribution, sample geometry, and matrix diffusivity are important considerations to prevent nucleation in the matrix. The mechanical restraint imposed on the sample is also critical to prevent cracking caused by the shrinkage of the sample.
A. Additive manufacturing of ceramic matrix composites (CMC);
B. The reinforcing material is dispersed in the ceramic resin that is sensitive to ultraviolet rays and can be printed by a standard light-curing 3D printer;
C. Convert to ceramic matrix composite material parts;
D. Examples of additively manufactured parts in polymer state and (E and F) states after pyrolysis;
G. Obtain SiOC matrix and ceramic particle reinforced parts.
Chemical modification allows SLA 3D printers to produce siloxane ceramic ceramic polymers, which can produce SiOC parts larger than 2 cm. The inclusion of reinforcing materials in this type of photocurable precursor ceramic resin will enable 3D printing of reinforced ceramic composite parts. Commercial 3D printers that can print polymer materials with heterogeneous media can be used to print ceramic precursor polymer materials. The entire structure of the 3D printing precursor ceramic shrinks after pyrolysis, which overcomes the main cracking mechanism of rigid fiber preforms.
Exploration direction and conclusion of new technology
Research in this field has achieved encouraging results, but the existing research lacks the effect of heterogeneous volume fraction on the pyrolysis conversion process and the resulting mechanical properties. The HRL research team stated in the paper that the purpose of their research is to inspect this by dispersing heterogeneity in a photocurable siloxane resin and using the reinforced SiOC ceramics of the DLP 3D printer. The particles will be used as a model enhancement system to simplify analysis and simplify the incorporation in the resin. HRL researchers will examine their effects on mass loss, shrinkage, notch sensitivity, and strength, and use the results to establish processing limits and guidelines for manufacturing high-quality additively manufactured ceramic matrix composite parts. Researchers will use whisker enhancers to obtain preliminary results and discuss potential directions for increasing processing range and performance.
In the above research, the HRL laboratory research team used light-curing 3D printing technology to manufacture SiOC ceramic composite materials, which are obtained by heat treatment of ceramic precursor materials containing siloxane containing inert reinforcing agents. In the end, the research team proposed based on the experimental structure that because the toughness, strength, and strength variability are comparable to those of traditionally processed ceramics, this additive manufacturing method can freely produce high-performance ceramic matrix composites and thicker ceramic parts than before.