B4C ceramics has extremely high hardness,but its fracture toughness is low.In order to improve the fracture toughness of B4C ceramics,the effect of introducing the second phase Al2O3 on the fracture toughness of B4C ceramics is studied,and the toughening mechanism of B4C-Al2O3 composite ce-ramics is explored.The results indicate that the addition of Al2O3 as the second phase can improve the fracture toughness of B4C ceramics.Among others,the fracture toughness of B4C-Al2O3 composite ceram-ics with 40％ Al2O3 reaches a maximum value of 4.96 MPa·m1/2.The toughening mechanism of B4C-Al2O3 composite ceramics is that Al2O3 grains experience cleavage cracking during the crack propagation,in-creasing the path of crack propagation;thus,part of crack propagation energy is consumed.Meanwhile,residual stress is generated between Al2O3 grains and B4C grains due to their thermal expansion mis-match.On the one hand,the compressive stress inside B4C grains is beneficial for inhibiting crack propa-gation.On the other hand,the tensile stress generated at the phase boundary between B4C grains and Al2O3 grains weakens the bonding of the phase boundary to some extent,leading to some cracks propa-gating along the phase boundary during the propagation process;therefore,some cracks are deflected,and so the fracture toughness of B4C-Al2O3 composite ceramics is improved.
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