Combined effect of SiC chopped fibers and SiC whiskers on the toughening of ZrB2

ZrB2-based composites were toughened by the simultaneous additions of SiC chopped fibers and SiC whiskers. The fracture toughness measured by Chevron Notched Beam in flexure was of the order of 6 MPa m1/2 and the 4-pt flexural strength around 500 MPa. The values of mechanical properties are compared to those of unreinforced ZrB2 and composites reinforced by solely fibers or whiskers in order to understand whether a synergistic whiskers-fibers toughening action is present or not in these composites. The combination of two different reinforcing agents is a successful strategy to obtain a super reinforcement provided that densification, reinforcing agents chemical integrity and secondary phases composition and amount are properly controlled.