Zirconium diboride (ZrB₂)–silicon carbide (SiC) composites are promising candidates for ultra-high temperature applications, yet optimizing their densification and mechanical performance without sintering additives remains a challenge. This study systematically investigates the independent and combined effects of three critical spark plasma sintering (SPS) parameters, that is, temperature, applied pressure, and dwell time, on the densification behavior, microstructure, and mechanical properties of ZrB₂–20 vol% SiC composites. Building upon prior work on powder preparation effects (e.g., Tungsten Carbide (WC) vs. ZrO₂ milling), this research uniquely focuses on how precise control of sintering conditions alone can tailor final material characteristics. The results demonstrate that optimizing sintering parameters yields significant property enhancement, achieving a maximum relative density of 99.2% (at 2100°C, 65 MPa, 15 min) and peak flexural strength of 516 MPa (at 2000°C, 65 MPa, 60 min). Hardness and fracture toughness reached 17.08 GPa and 3.85 MPa m^1/2, respectively, under optimized conditions. Through detailed microstructural and performance analysis, this work explains the fundamental role of individual sintering parameters in governing densification kinetics and mechanical outcomes. The findings offer practical guidance for additive-free, energy-efficient processing of ZrB₂–SiC ceramics for advanced aerospace and thermal protection systems.

This study investigates the impact of different powder milling methods on the densification and mechanical properties of ZrB₂-SiC ceramic composites processed via spark plasma sintering (SPS). Powders were prepared using two ball milling techniques: tungsten carbide (WC) and conventional ZrO₂. The densification behavior during SPS was monitored, and the sintered samples were evaluated for their relative density, hardness, fracture toughness, and flexural strength. Results show that WC milling significantly enhances densification, achieving 99.2 % relative density at 2100 °C/65 MPa/15 min, compared to 96.5 % for ZrO₂-milled samples. This improvement is due to WC's sintering aid effect, which promotes grain boundary diffusion and particle packing. However, ZrO₂-milled composites exhibit superior hardness (17.38 GPa) and fracture toughness (3.97 MPa m¹/²), attributed to their refined grain structure and the absence of softer ZrO₂ phases. Conversely, WC-milled samples show slightly higher flexural strength (384–516 MPa), likely due to the transformation toughening effect of the secondary ZrO₂ phase. Overall, WC milling improves densification and flexural strength, while ZrO₂ milling yields finer-grained composites with higher hardness and toughness, making it better suited for wear-resistant and mechanically demanding applications.