Phase tailoring of (Zr,Ti)B2-(Zr,Ti)C-SiC ceramics toward microstructural optimization for simultaneous enhancement of strength and toughness

To address the challenges of achieving densification at lower sintering temperatures and precise control over the microstructure in UHTCs-SiC, a novel reactive hot-pressing sintering technology was proposed to realize the low-temperature densification of fine and uniform (Zr,Ti)B 2 -(Zr,Ti)C-SiC ceramics, as well as the accurate tailoring of phase compositions. The intrinsic relationship between phase compositions, microstructural tailoring and mechanical performance was revealed. As the molar ratio of (Zr,Ti)C/(Zr,Ti)B 2 decreases, rod-shaped microstructural units (ultra-high temperature borides) progressively develop within the ceramic. These elongated features play a beneficial role in deflecting propagating cracks. When coupled with equiaxed (Zr,Ti)C grains, this combination allows the synergistic strengthening and toughening mechanisms to be fully activated, so the (Zr,Ti)B 2 -(Zr,Ti)C-SiC ceramics with a (Zr,Ti)C/(Zr,Ti)B 2 molar ratio of 1:2 exhibit a flexural strength of 479.2 MPa and a fracture toughness of 3.84 MPa·m 1/2 , which are 62.2 % and 40.7 % higher than those of (Zr,Ti)C-SiC ceramics, respectively.