In situ synthesis of ZrB2–ZrCx ceramic tool materials toughened by elongated ZrB2 grains

ZrB2–ZrCx ceramic tool materials toughened by elongated ZrB2 grains were fabricated via an in situ reactive hot pressing process. The product showed an excellent fracture toughness of 9.69 MPa m1/2 and a flexural strength of 898.13 MPa. The high fracture toughness and flexural strength were ascribed to the in situ formation of elongated ZrB2 grains and the interlocking structure in the composites. The toughening mechanisms by the discontinuous elongated ZrB2 grains were crack deflection, grain bridging and grain pullout effects. The microstructure, mechanical properties and relative density can be tailored by manipulating the molar ratio of Zr to B4C. The carbon vacancies in the ZrCx phase promoted the densification, however, led to a sharp decrease in hardness. The elongated ZrB2 grains were not found after adding 2 wt.% Ni into the raw materials.