High‐strength high‐thermal‐conductivity Al 2 O 3 ceramics via colloidal processing and low‐temperature pressureless sintering

Abstract There are growing interests to produce fine ceramics at lower temperatures and less energy consumption while maintaining competitive properties for existing and new applications. Strong alumina ceramics (e.g., with flexural strength >800 MPa) with high thermal conductivity are useful in industrial applications, yet difficult to prepare with by cost‐effective and shape‐flexible pressureless sintering. For brittle ceramics such as pure alumina, one effective way for strengthening is to refine flaw size via advanced forming technique. Here, we report progresses in colloidal processing and direct casting of high‐solid‐loading (up to 56 vol%) alumina (average particle size of 120 nm) slurry and pressurelessly sintered alumina ceramics with low sintering temperature (1350°C), low sintering shrinkages (16.3%), high sintered density (3.98 g/cm 3 ), high flexural strength (914 ± 154 MPa), and high thermal conductivity (35.2 ± 0.5 W/(m K)). Experimental evidence has demonstrated different sensitivity of flexural strength and thermal conductivity on flaw/residue porosity of the sintered samples. Our results offer valuable guidance on the design and processing of multifunctional ceramics for optimal in‐service performance.