Effect of HfSi2-induced intergranular liquid phase on densification behavior of ZrB2

The densification behavior and mechanical properties of ZrB2-based composites were investigated. The results demonstrated that the fully dense ZrB2-based composites could be obtained at lower sintering temperature (1600 degrees C) and pressure (30 MPa) when the content of HfSi2 was above 20 vol.%. The as-sintered composite was a special core-shell structure, with ZrB2 as the core and (Zr, Hf)B-2 solid solution as the shell. The core-shell structure resulted from the diffusion of Hf atom into the boride matrix, which could accelerate the densification. In addition, the intergranular liquid phase induced by the HfSi2 addition filled the micropores of the composites effectively during the sintering. When the content of HfSi2 increased to 20 vol.%, its compressive strength, hardness, and fracture toughness all reached the maximum values, which were 1617 MPa, 15.99 GPa, and 2.44 MPa m(1/2), respectively.