Researchers have developed a novel approach to fabricate SiOC-WOx ceramic matrix composite films with gradient properties, addressing the challenges of achieving both high toughness and stiffness in ceramic materials. By integrating hybrid nanoparticle inkjet printing and selective laser sintering, the team has created films reinforced with nanoscale tungsten-based particles that exhibit superior mechanical properties and interfacial bonding strength.
Ceramic films play a crucial role in reinforced coatings, protecting metallic substrates against wear, corrosion, and high-temperature creep. These ceramic-reinforced metallic materials find applications in various industries, including aerospace, precision sensors, and energy storage. However, traditional ceramic materials suffer from low fracture toughness and tensile strength, leading to sudden plastic deformation under heavy loads.
To overcome these limitations, the researchers focused on developing CMC materials, where the matrix phase is reinforced by doping phases composed of fibers or nanoparticles. The sintering of these multiphase nanoparticles results in a distinctive distribution structure within the CMC components, enhancing toughness and strength. While CMCs have found applications in bulk materials, their use in thin films has been limited due to the incompatibility of conventional thin film deposition techniques with composite thin film preparation.
The researchers employed an inkjet printing method to deposit a nano-ink suspension containing SiC and W nanoparticles in a specific pattern. After the evaporation of the solvent, the residual nanoparticles on the target substrate were sintered with a laser into a densified film. The gradient performance of the film was established through two mechanisms: the stratification of SiC and W nanoparticles due to density differences during the evaporation of sessile nano-ink droplets, and the variations in energy distribution and oxygen content during laser sintering, which drove diverse degrees of sintering and oxidation at different depths.
The resulting SiOC-WOx films exhibited remarkable mechanical properties, with a 2-fold improvement in hardness and modulus, and a 3.8-fold better fracture toughness compared to the matrix material. Moreover, the films demonstrated interfacial bonding strengths of up to 86.6 MPa and stable operation at temperatures as high as 1050 °C. These enhanced properties are attributed to the gradient in the metal-to-ceramic composition and the uniformly dispersed self-assembled nanoscale reinforcing particles.
The external surface of the SiOC-WOx film consists primarily of a dense glass phase SiO2 with high hardness and oxidation resistance, while the internal layer gradually transitions to a metallic state. This gradient structure not only improves the toughness and interfacial bonding strength of the ceramic coating but also serves as a transition layer, effectively addressing interfacial bonding issues arising from mismatches in the coefficient of thermal expansion between the ceramic layer and the metal substrate.
The laser sintering of hybrid nanoparticles, as demonstrated in this study, has the potential to be extended to various metallic, semiconducting, and insulating ceramic nanomaterials for the production of gradient films. This method offers a promising approach to fabricate ceramic films with meticulously controlled compositions and properties, leveraging the high throughput capabilities of directly written hybrid nanoparticles.
