Microstructural Evolution and Mechanical Response of Al 2 O 3 –3YSZ–MWCNT Hybrid Ceramic Composites Consolidated by Spark Plasma Sintering

This study investigates the microstructural evolution and mechanical response of spark plasma sintered Al 2 O 3 –3 mol% yttria‐stabilized zirconia (3YSZ)–multi‐walled carbon nanotube (MWCNT) hybrid ceramic composites with systematically varied reinforcement architectures. Bimodal α‐Al 2 O 3 powders containing micron‐ and nano‐sized fractions were combined with 3YSZ and MWCNTs, followed by ball milling and spark plasma sintering (SPS) consolidation at 1400°C. X‐ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE‐SEM), energy‐dispersive x‐ray spectroscopy (EDS), and quantitative ImageJ analysis were used to evaluate phase constitution, microstructural evolution, and feature‐size characteristics. The composites achieved relative densities of 98.8%–99.7%, with retention of the intended ceramic and graphitic constituents and no detectable crystalline carbide formation. Analysis of 56 FE‐SEM micrographs comprising 473 709 segmented features revealed pronounced composition‐dependent differences in feature‐size populations. AYC exhibited the finest and comparatively compressed population, with D 50 = 1.505 µm, D 90 = 3.756 µm, and a 0.5–1 µm fraction of 9.522%, whereas AY showed the broadest distribution, with D 90 = 7.376 µm and a distribution span of 3.141. Feature refinement did not directly translate into higher densification, as AYC exhibited the lowest relative density of 98.8% ± 0.3%. A showed the highest hardness of 1976 ± 30 HV5 (19.38 ± 0.29 GPa), whereas AYC achieved the highest indentation fracture toughness of 4.93 ± 0.10 MPa m 1/2 , representing a 16.3% improvement over A. These findings indicate that hybrid reinforcement architecture can influence microstructural refinement and fracture resistance in highly consolidated Al 2 O 3 ‐based ceramics.