Oxide Ceramic matrix composites (Ox-CMCs) combine excellent strength, chemical resistance, and thermal stability. These qualities make them suitable for components exposed to harsh and oxidative environments, such as gas turbine engines and thermal protection systems.
However, maintaining these properties at high temperatures is challenging due to grain coarsening and degradation above 1000°C. A recent study, “Enhancing Thermal Stability of Oxide Ceramic Matrix Composites via Matrix Doping,” investigated strategies to address these issues.
Baikowski® contributed to the study with its high-purity alumina BA15 powder, which was selected for its particle size distribution (d₅₀ = 120 nm) and exceptional chemical purity. These attributes ensured a consistent and reliable matrix material, critical for evaluating the effects of doping. For that, water-based ceramic suspensions containing a solid content of 50 vol% were prepared.
For more information, explore our range of products for CMCs , including BA15 powder and our latest innovation, SLAZ, a high-purity alumina slurry doped with Mathym’s zilight® nano-zirconia.
Materials and Methods
Composites reinforced with Nextel 610 fibers and alumina matrices were produced in two variations: one using non-doped alumina and the other doped with 480 ppm MgO.
MgO was chosen due to its recognized ability to inhibit grain boundary mobility and reduce grain growth, making it an effective doping agent for enhancing thermal stability.
Fabricated through an ionotropic gelation technique, the composites were sintered at 1200°C, followed by heat treatments at 1300°C and 1400°C. SEM, WDX, and tensile strength tests were conducted to assess the microstructural and mechanical impacts of doping.
CMC Performance With Baikowski’s Doped Alumina
Microstructural Findings:
- Both doped and non-doped composites had similar initial microstructures with uniform equiaxial grains.
- Thermal exposure induced grain growth in both samples, but MgO-doped composites showed smaller, more refined grains and significantly fewer abnormal grains, especially near the fiber regions.
Elemental Interactions:
- WDX analysis showed that silicon (Si), which is part of the Nextel 610 fibers, diffuses outward toward the matrix after heat exposure, while magnesium (Mg) from the matrix diffuses slightly into the fibers.This interaction helped suppress excessive grain coarsening in MgO-doped composites, leading to narrower fiber grain size distributions and smaller grains compared to non-doped samples, resulting in the reduction of strength loss after heat treatments.
Mechanical Performance:
- Both types of composites had comparable tensile strength (~135 MPa) in the as-processed state.
- Post-heat treatment, MgO-doped composites retained higher tensile strength, with reductions of 8% at 1300°C and 41% at 1400°C, compared to 27% and 62% reductions for non-doped samples.
The study highlights the benefits of matrix doping for thermal stability enhancement of Ox-CMCs, particularly when using high-purity, MgO-doped alumina from Baikowski®. The customized alumina matrix effectively reduced fiber grain growth and preserved mechanical properties under high-temperature conditions.
Baikowski®’s ability to deliver tailored solutions through strong R&D capabilities and close collaboration with industry ensures its alumina powders meet stringent application demands. These advancements further position Baikowski® as a trusted partner in developing high-performance materials for the aerospace sector and other high-temperature applications.
Learn more by downloading our dedicated White Paper👇
