YSZ nanocomposite films with gradient properties fabricated by laser sintering of hybrid nanoparticles

The development of ceramic films/coatings on metal surfaces holds significant promise for enhancing metal properties such as hardness, temperature resistance, and corrosion resistance. This research is particularly pertinent across diverse sectors including aerospace, medica, and semiconductor industries. Yttria-stabilized zirconia (YSZ) stands out as the prevailing ceramic thin-film material in aero-engines due to its exceptional high-temperature characteristics, notably strain tolerance and low thermal conductivity. Nonetheless, the inherent limitation in YSZ's fracture toughness and the disparity in coefficient of thermal expansion (CTE) between YSZ and metal substrates present formidable challenges to its durability. While the nanocomposite structures in YSZ films and the fabrication of transition layers between superalloys and YSZs have shown promise in mitigating these issues individually, the simultaneous realization of both remains elusive. This study proposes a novel approach to fabricate YSZ nanocomposite gradient transition films by integrating inkjet printing and laser sintering techniques. The inkjet printing ink is formulated with precise ratios of 8YSZ, ZrC, SiC, and W nanoparticles. During the inkjet printing process, the variation in particle density facilitates the gradient distribution of the composition. Subsequently, during laser sintering, this gradient property is further accentuated owing to differences in energy distribution and oxidation degree, culminating in the formation of thin films with progressively varying physical properties from ceramic (surface) to metal (inner layer), which alleviates the CTE mismatch problem. In addition, the YSZ films exhibit a composite structure reinforced by nanoscale W and YSZ particles, due to the higher melting point of W and YSZ nanoparticles (compared to SiC), which improves the fracture toughness of ceramic films. The composite gradient YSZ films thus synthesized exhibit notable mechanical properties, including high fracture toughness (> 3.8 MPam^0.5), substantial interfacial bonding strength (> 85 MPa), elevated surface hardness (> 18 GPa), and exceptional high-temperature performance (including insulation and cycle life). The success of fabricating high-performance YSZ composite gradient films by laser sintering of hybrid nanoparticles demonstrates how future thin film development can accelerate the discovery of revolutionary materials by utilizing combinatorial nanomaterials and bottom-up additive manufacturing processes.