Toward a low‐temperature sintering of carbon fiber toughened high entropy boride composite with Co addition

Abstract Dense C f /(ZrHfNbTaCr)B 2 –SiC (CBS‐Co) composite is successfully prepared at a low temperature of 1500°C by adding 5 vol.% Co. Liquid Co accelerates the particle rearrangement and significantly enhances the relative density of CBS‐Co (95.2%). In situ formed Co 2 B phase by diffusion reaction bonds tightly with high entropy diboride (HEB) and SiC grains in CBS‐Co. Due to the promotion of relative density and interfacial bonding strength, CBS‐Co exhibits a high flexural strength (283 ± 23 MPa). Structural damages of carbon fibers are effectively prevented by compact fiber coating. The well‐preserved fibers play dominant roles to increase the fracture toughness of CBS‐Co (4.77 ± .5 MPa·m 1/2 ). Moreover, SiO 2 ‐rich oxide layer can effectively heal flaws and inhibit oxygen diffusion, achieving relatively high flexural strength after oxidation at 1300°C of CBS‐Co composite. This work provides a stepping stone for developing high‐performance carbon fiber toughened HEB composites based on low temperature liquid‐phase sintering technology.