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The effect of addition of submicrometer-sized B 4 C (5,10 and 15 wt%) on microstructure, phase composition, hardness, fracture toughness, scratch resistance, wear resistance, and thermal behavior of hot-pressed ZrB 2 -B 4 C composites is reported. ZrB 2 -B 4 C (10 wt%) composite has V H1 of 20.81 GPa and fracture toughness of 3.93 at 1 kgf, scratch resistance coefficient of 0.40, wear resistance coefficient of 0.01, and ware rate of 0.49 9 10 À3 mm 3 /Nm at 10N. Crack deflection by homogeneously dispersed submicrometer-sized B 4 C in ZrB 2 matrix can improve the mechanical and tribological properties. Thermal conductivity of ZrB 2 -B 4 C composites varied from 70.13 to 45.30 W/m K between 100°C and 1000°C which is encouraging for making ultra-high temperature ceramics (UHTC) component.

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