Pressureless sintering behavior of ZrC ceramic particles encapsulated by nano-sized carbon layer

The typical high-density zirconium carbide (ZrC) ceramic requires high temperature and high pressure, leading to high manufacturing cost for complex shapes. Herein, nano-sized carbon layer encapsulated ZrC particles were pressureless sintered to achieve near-net preparation of high-density and complex-shape ZrC ceramic. The results indicate that reaction between carbon layer and the ZrCxOy phase in ZrC was improved because the carbon layer shortened the oxygen diffusion pathway. The oxygen content decreased from 3.52 wt% to 0.82 wt% while the thickness of carbon layer decreased from 4.0 nm to 0.75 nm after sintering at 1950 °C for 1 h. Furthermore, the migration of oxygen from ZrCxOy phase to the carbon layer effectively facilitate the formation and growth of the sintering neck. The resulting ZrC ceramic exhibited a high relative density of 92.3 % and excellent mechanical properties. The Vickers hardness, indentation fracture toughness, micro hardness, elastic modulus, and flexural strength were 17.3 ± 0.7 GPa, 4.0 ± 0.5 MPa m1/2, 22.2 ± 2.4 GPa, 429.9 ± 20.7 GPa, and 324 ± 8 MPa, respectively. This work provides a novel perspective to fabricate near-net, high-density and complex-shape ZrC ceramic at lower temperature without pressure.