Damage tolerance and R-curve behavior of ZrB2–ZrO2 composites

Four ZrB2 composites were prepared by hot-pressing with different content of ZrO2, i.e., 0, 10, 20 and 30 vol%. By means of the indentation-strength method, damage tolerance and resistance-curve (R-curve) behavior were investigated for ZrB2–ZrO2 composites. Under the indentation load of 196 N, retained strength of monolithic ZrB2 was only ∼89 MPa, however, that value could reach ∼281 MPa for ZrB2–30 vol%ZrO2 composite. Obvious R-curve behavior was further found in ZrB2–ZrO2 composites compared with monolithic ZrB2. Regarding ZrB2–30 vol%ZrO2, the steady-state toughness was ∼6.5 MPa m1/2. Such improved toughening effect was attributed to the crack bridging and transformation toughening of ZrO2.