Pressureless sintering and properties of additively manufactured ZrB2–SiC.

Densification behavior, grain growth kinetics, mechanical and thermal properties of pressurelessly sintered zirconium diboride–silicon carbide (ZrB2–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 ZrB2 and SiC followed a normal grain growth power law with grain growth exponent <italic>n</italic> = 2 indicating diffusion‐controlled coarsening. The activation energies for grain growth were 267 ± 10 kJ/mol for ZrB2 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. [ABSTRACT FROM AUTHOR]