Ultrahigh-temperature ceramics (UHTCs) are designed to withstand extreme environments, making them indispensable in aerospace, defense, and energy applications. Hafnium carbide (HfC) in particular is well-suited for thermal protection coating systems in spacecraft, engines, and hypersonic vehicles, due to its ultrahigh melting point, exceptional hardness, high elastic modulus, and high thermal conductivity. But achieving high-purity HfC with consistent properties on a large scale remains a challenge. High cost and limited scalability constrain widespread adoption. A technique for synthesizing HfC, developed by a team at North Carolina State University, integrates crosslinking and pyrolysis into a single step, reducing processing time and energy consumption. The technique falls into the category of selective laser reaction pyrolysis (SLRP) processing, where laser excitation simultaneously induces polymer precursor-to-ceramic conversion and pyrolysis, enabling the rapid synthesis of refractory ceramics without the need for prolonged exposure to high-temperature furnaces. A laser technique for synthesizing hafnium carbide (HfC) could transform ultrahigh temperature ceramic (UHTC) manufacturing for space, defense, and energy applications. Courtesy of North Carolina State University. “Traditionally, sintering HfC requires placing the raw materials in a furnace that can reach temperatures of at least 2200 ºC — a process that is time-consuming and energy-intensive,” professor Cheryl Xu said. “Our technique is faster, easier, and requires less energy.” The technique uses a liquid polymer precursor combined with laser-based processing. A 120-W laser is applied to the surface of a liquid polymer precursor in an inert environment, such as a vacuum chamber or a chamber filled with argon. The CO2 IR laser enables localized heating up to 2000 °C within seconds, facilitating the conversion of the liquid polymer precursor into HfC. The researchers characterized the ceramic material using x-ray diffraction and microscopy. They confirmed the crystallinity and phase purity of the synthesized HfC powder. To investigate energy absorption, the researchers added thermal- and photoactivators to the precursor before laser exposure. They found that the thermal activator had a negligible impact on reflectivity but yielded a pure HfC phase, suggesting there is the potential to optimize precursor formulations to enhance efficiency without compromising purity. “It is actually a bit of an oversimplification to say that the laser is only sintering the liquid precursor,” Xu said. “It is more accurate to say that the laser first converts the liquid polymer into a solid polymer and then converts the solid polymer into a ceramic. However, all of this happens very quickly — it is essentially a one-step process.” Using the new sintering technique with additive manufacturing, the researchers deposited HfC coatings onto carbon-carbon composite substrates. The ceramic coating bonded to the underlying structure and did not peel away. The ability to directly integrate HfC coatings into carbon-carbon substrates without furnace sintering could open new possibilities for high-temperature aerospace and energy applications. “The HfC coatings on [carbon-carbon] substrates demonstrated strong adhesion, uniform coverage, and potential for use as thermal protection and an oxidation resistant layer,” Xu said. “This is particularly useful because, in addition to hypersonic applications, carbon/carbon structures are used in rocket nozzles, brake discs, and aerospace thermal protection systems such as nose cones and wing leading edges.” The liquid precursor can be used to coat an underlying structure, such as the carbon composites used in hypersonic technologies like missiles and space exploration vehicles. The precursor can be applied to the surface of the structure and then sintered with a laser. “Because the sintering process does not require exposing the entire structure to the heat of the furnace, the new technique holds promise for allowing us to apply ultrahigh temperature ceramic coatings to materials that may be damaged by sintering in a furnace,” Xu said. The laser sintering technique achieved a crosslinked polymer to HfC ceramic yield of up to 54%, which is 18% higher than the yield reported for furnace-based HfC synthesis with a 4-h holding time. “Our technique allows us to create ultrahigh temperature ceramic structures and coatings in seconds or minutes, whereas conventional techniques take hours or days,” Xu said. “And because laser sintering is faster and highly localized, it uses significantly less energy.” Additionally, compared to traditional sintering methods, the new technique is relatively portable. “Yes, it has to be done in an inert environment, but transporting a vacuum chamber and additive manufacturing equipment is much easier than transporting a powerful, large-scale furnace,” Xu said. The technique for synthesizing UHTCs could advance the field of laser-based additive manufacturing and contribute to the development of next-generation UHTC materials with improved processing efficiency, scalability, and design flexibility. Xu and her team are open to working with public and private partners to transition the new technology for use in practical applications. The research was published in the Journal of the American Ceramic Society (www.doi.org/10.1111/jace.20650).