Pressureless sintering and properties of additively manufactured ZrB 2 –SiC

Densification behavior, grain growth kinetics, mechanical and thermal properties of pressurelessly sintered zirconium diboride–silicon carbide (ZrB 2 –SiC) fabricated by extrusion of high solids loading pastes have been studied. The effects of sintering temperature (1600–2300°C), heating rate during constant heating rate sintering (10–50°C/min), and time during isothermal sintering (3–24 h) on density and grain size were examined. The apparent activation energy for densification was determined to be 940 ± 90 kJ/mol, suggesting lattice diffusion as the dominant sintering mechanism. Grain growth of both ZrB 2 and SiC followed a normal grain growth power law with grain growth exponent n = 2 indicating diffusion‐controlled coarsening. The activation energies for grain growth were 267 ± 10 kJ/mol for ZrB 2 and 264 ± 15 kJ/mol for SiC. Sintered microstructures were homogeneous with relative densities of 95%–99% depending on heat treatment schedules. Flexural strength (270 ± 40 MPa) was lower than hot‐pressed materials of equivalent composition by a factor of two or more due to the presence of pores originating from paste inhomogeneities. Young's modulus (482 ± 20 GPa) and Vicker's microhardness (22 ± 5 MPa HV0.2), as well as thermal diffusivity and thermal conductivity up to 1800°C were found to be comparable to hot‐pressed materials.